Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/11/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1045 PM EST Fri Dec 10 2021
.SYNOPSIS...
An approaching storm system will bring some light rain to the
region towards daybreak Saturday. Some sheltered areas could
briefly see this start out as light freezing rain. With milder
temperatures moving into the region, rain showers and gusty
winds are expected throughout the day on Saturday. Behind the
storm`s cold front, strong winds are expected for Saturday night
as rain ends, with some cooler temperatures moving back into
the region. Breezy and dry weather is expected for Sunday with
temperatures closer to seasonal levels.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A Winter Weather Advisory for freezing rain is in effect for 3
to 8 am Saturday for southern Adirondacks and Glens Falls area
including northern Washington County of eastern New York and for
southern Vermont.
Update 1015 PM EST...Temperatures have dropped off a bit more
than expected in some locations. However, clouds will continue
to increase and lower across the area and winds will pick
overnight resulting in temperatures beginning to rise. With
precipitation not expected until late at night don`t see a need
to expand the winter weather advisory.
Update 7 PM EST...Forecast is on track with warm air advection
precipitation not expected to develop across the area until late
at night. It`s mild for an early December evening with temperatures
in upper 20s to upper 30s across the forecast area. Temperatures
will drop some before stabilizing then beginning to rise late at
night. Skies across the southern part of the forecast area have
become mostly clear but clouds will move back in as the night
progresses. Only some minor adjustments were needed.
Previous Discussion 353 PM EST...Upper level ridging over the
far southeastern US extends northeast offshore into the Western
Atlantic. Meanwhile, a large upper level trough is shifting from
the Rockies towards the High Plains for tonight. As a result of
this pattern over the CONUS, our region is under the influence
of broad west-southwest flow aloft. Surface high pressure has
been in control of the weather through the day today, but will
be departing off to the east for tonight.
IR satellite imagery continues to show plenty of clouds in
place over the region, although there have been some breaks from
time to time. Skies may initially be partly cloudy this evening
which will allow for temps to fall. After midnight, however,
clouds will start increasing once again, as a surface warm front
off to the southwest starts approaching. With a developing light
south to southeast breeze, temps will stop falling and actually
hold steady or even start to rise. Lows around midnight should
be in the upper 20s to low 30s.
Some light rain will start moving into the area from the
southwest after about 5 or 6 AM or so. While most areas will be
above freezing when precip begins, some sheltered areas of the
Adirondacks and southern Greens could see surface temps right at
32 degrees, allowing for a brief period of freezing rain. While
ice amounts will only be a trace to a hundredth or two, it may
be enough to make any exposed surfaces slick. A Winter Weather
Advisory is in effect for these areas beginning at 3 AM
(although best chance for seeing freezing precip will likely be
a short duration after 5 or 6 AM).
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The warm front will continue to lift northward across our area
on Saturday morning as the strong surface storm lifts towards
the Great Lakes. A period of steady light rain looks to occur,
with any lingering freezing rain within the sheltered mountain
valleys changing to plain rain by 8 or 9 AM. The light rain
associated with the warm advection/isentropic lift should be
ending towards Noon. Behind the warm front, a gusty southerly
winds will take over for Sat afternoon, allowing for surface
temps to warm considerably, despite the clouds and calendar
showing December. Most of the area will be well into the 50s by
Saturday afternoon, with some spots in the mid Hudson Valley
coming close to 60 by late in the day. The southerly winds will
be gusting up to 30 mph at times, although the strong inversion
around 900 hpa will prevent winds from getting too strong ahead
of the approaching frontal boundary. While there may be a few
patches of drizzle or light showers during the afternoon, most
of the time should be fairly dry as our area will be between
the best forcing.
By the evening hours, the storm`s cold front will be approaching
from the west as the surface low pressure lifts into southern
Canada and a more organized line of showers will be heading
towards the area. According to both the 3km HRRR and NAMNest, it
should be crossing from west to east from 7 to 10 PM. Some
locally heavy downpours may accompany the fine line of showers
that moves across the area. Model sounding shows some elevated
instability, so can`t rule out a rumble of thunder as well and
have included that slight chance in the forecast as well. Some
gusty winds may accompany the showers as well, although the best
chance for gusty winds looks to be immediately behind the
boundary.
As cooler air moves in aloft, both good mixing and a strong
pressure gradient in place will allow for strong westerly winds
for Saturday night, especially for areas north and west of the
Capital Region. Some gusts may reach 50 mph, especially for the
Adirondacks, Mohawk Valley, Greater Capital Region and
Berkshires. Some downed trees/power lines are possible and a
Wind Advisory is in effect for much of the area for Sat evening
into Sat night. Precip should shut off for most areas as the
front crosses, although some lingering lake-effect rain/snow
showers can`t be ruled out for the western Adirondacks for the
late night hours, where a light dusting of snow is possible as
well. Temps will fall into the mid 20s to mid 30s, although most
larger valley areas will remain above freezing for Sat night.
Drier, breezy and cooler weather is expected for Sunday into
Sunday night. Any lingering lake effect activity over the
Adirondacks or Mohawk Valley should wind down on Sunday morning
and skies will be clearing out. Surface high pressure will be
passing by to the south, so enough of a pressure gradient will
remain in place to keep it fairly breezy through the day on
Sunday, with some gusts still up to 25 mph. Daytime temps will
range from the mid 30s to mid 40s. Skies should remain fairly
clear into Sunday night, although a light breeze may linger.
With the light breeze and lack of snow cover, it won`t be too
cold for Sunday night, with lows in the upper 20s to low 30s.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
Weak cold front with little to no moisture tracks through Monday
into Monday night and high pressure will build in from Canada
Tuesday, exiting SE Canada Wednesday. Highs Monday in the mid 40s
to around 50 with around 40 higher terrain. Highs Tuesday behind the
cold front, in the mid to upper 40s with upper 30s higher terrain.
Warm advection begins Wednesday and based on the low level ridging
in SE Canada building offshore New England, onshore low level flow
and boundary layer warming and moisture advection could increase the
clouds very quickly late Tuesday night through Wednesday, limiting
the sun. So, highs Wednesday in the mid to upper 40s with upper 30s
to around 40 higher terrain.
Strengthening warm advection and moisture advection as well as
isentropic lift Wednesday night into Thursday as a strong upper
impulse and associated cold front approach our region. Spotty mixed
precipitation is possible late Wednesday night. Then a potential
warm up to temperatures in the 50s Thursday with showers ahead and
along a strong cold front. Temperatures near 50 in higher terrain.
The front tracks through Thursday afternoon and night and weak cold
advection returns Friday. Based on the long wave pattern, the cold
advection will be similar to past cooldowns in recent weeks, with
temperatures cooling to near or a little above normal because the
deepest and coldest air is still locked up well north of the U.S.
lower 48 states. Highs Friday in the mid 40s to around 50 with upper
30s to around 40 higher terrain.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Area of partial clearing tracking into our region with some
scattered variable clouds at around 5000 feet and higher. This area
of scattered variable broken cloudiness will exit our region as the
leading edge of developing precipitation and solid cloud cover
approaches from central and western PA/NY. So, VFR conditions until
about 10Z, when the leading edge of the clouds and precipitation
begin to affect the TAF sites.
Temperatures around KGFL will be near freezing, so while the highest
probability is for rain to begin at KGFL around 10Z, there could be
a few hours of freezing rain between 10Z-13Z, where a PROB30 is
included. Elsewhere, precipitation should start as just rain.
Temperatures will warm by around 13Z to change any freezing rain at
KGFL to just rain.
Rain will be fairly widespread through about 15Z-18Z with MVFR
ceilings and visibilities at all TAF sites. Some intervals of
steadier precipitation may continue at KGFL into the afternoon, but
at KALB, KPSF and KPOU, a lull in the steadier precipitation is
likely until the showers associated with the cold front approach by
around 21Z-22Z. Just keeping VCSH from around 18Z-21Z until the
showers with the cold front move in.
So, during the lull, still, some MVFR ceilings but visibilities will
trend to VFR. Then once the showers move in to all TAF sites with
the cold front around 21Z, visibilities trend to borderline MVFR/IFR
and ceilings drop to IFR. The MVFR/IFR conditions and showers
continue through 24Z.
Winds tonight from the southeast to south at 10 Kt or less,
sometimes less than 3 Kt at KPOU, KGFL and KPSF. Then around
daybreak, steady south winds at around 10 Kt, increasing to 15 to 20
Kt by afternoon. KALB and KPSF could gust around 25 to 35 Kt in the
afternoon.
WInd shear is expected at all TAF sites by around 10Z as winds at
2000 feet should be south to southwest at 40 to 55 Kt through the
day. Once surface winds become gusty at KALB in the afternoon, the
wind shear should end, but wind shear continues at all other TAF
sites through the day.
Outlook...
Saturday Night: High Operational Impact. Windy. Definite SHRA.
Sunday: Low Operational Impact. Breezy.
Sunday Night through Wednesday: No Operational Impact. NO SIG WX.
&&
.HYDROLOGY...
Although dry weather is expected this evening, a frontal system
will begin bringing some light rainfall to the region towards
daybreak Saturday. It may initially begin as freezing rain in
some sheltered areas, but the majority of the precip will be
just plain rain with this system. Showers will occur during the
day Saturday, especially just ahead of the storm`s frontal
boundary during the evening hours. Total precipitation amounts
will range from around a third of an inch across southern areas
to a little over an inch across the Adirondacks. This rainfall
will lead to rises on rivers and streams, but no flooding is
expected.
Drier weather returns Sunday into early next week, which would
allow river levels to gradually recede.
For details on specific area rivers and lakes, including observed
and forecast river stages and lake elevations, please visit the
Advanced Hydrologic Prediction Service /AHPS/ graphs on our
website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Wind Advisory from 5 PM Saturday to 4 AM EST Sunday for NYZ032-
033-038>043-047>054-058>061-063-082>084.
Winter Weather Advisory from 3 AM to 8 AM EST Saturday for
NYZ033-041>043-082-083.
MA...Wind Advisory from 5 PM Saturday to 4 AM EST Sunday for MAZ001-
025.
VT...Winter Weather Advisory from 3 AM to 8 AM EST Saturday for
VTZ013>015.
&&
$$
SYNOPSIS...IAA/Frugis
NEAR TERM...IAA/Frugis
SHORT TERM...Frugis
LONG TERM...NAS
AVIATION...NAS
HYDROLOGY...Frugis
Area Forecast Discussion
National Weather Service Gaylord MI
957 PM EST Fri Dec 10 2021
.UPDATE...
Issued at 947 PM EST Fri Dec 10 2021
Strong surge of warm air advection driven precipitation driving
north across the area this evening...well ahead of deepening
surface low across southeast Iowa. Leading edge of this
precipitation across northern lower Michigan taking the form of a
wintry mix, with a quick transition to just plain rain as surge of
elevated warm air spreads north. Expect this precipitation to
continue to expand north into eastern upper Michigan, where snow
will remain the primary precipitation type for much of the
overnight. Expect several inches of wet snow for this area,
especially across northwest Chippewa County. Warm nose does make
it into eastern sections of eastern upper Michigan late,
supporting a transition to a wintry mix of precipitation. Expect a
full transition to rain for areas south of the big bridge, but
not before an inch or two of slop falls across interior areas in
the tip of the mitt. May even hear a few rumbles of thunder late
across our southeast counties as that area gets into the warm
sector with surface low tracking into northwest lower Michigan
toward morning.
Per coordination with Grand Rapids forecast office, have gone
ahead and expanding inherited wind advisories to all of northern
lower Michigan late Saturday morning and afternoon. Latest HRRR
guidance shows widespread wind gusts of over 40 mph within surge
of cold air advection behind departing deepening surface low.
&&
.NEAR TERM...(Through Tonight)
Issued at 336 PM EST Fri Dec 10 2021
...Messy winter storm arrives this evening...
High Impact Weather Potential...High. Accumulating snow in
portions of Eastern Upper.
The main wave continues to dig through the central Rockies this
afternoon with a 120kt jet extending from it into the Great Lakes.
The 990mb surface low has moved into southwest Iowa, and is forecast
to intensify and track into central Lake Michigan just after
midnight tonight..supported along by great dynamic support thanks to
the incoming wave and UL jet. Convection has broken out over
Missouri and Illinois along the warm front which has been slowly
moving northward...with some midlevel moisture over-running it into
the Chicago/southern Michigan region. Still believe we`ll take a
while to saturate the column given the quite dry antecedent mid-
level air this morning. Better forcing ahead of the wave arrives in
our area right around 00Z...this area of forcing is currently
supporting the convection in NO/IL. Thus believe we`ll see some
decent rainfall overnight. PWAT`s approach 0.90" overnight in the
southeastern third of the CWA, which is much above normal (by 3 to 4
St. Dev!) for mid-December.
One question is when exactly rain moves into the southwest counties
this evening. Guidance has been fairly consistent with the column
saturating by 00Z, but don`t know if we could squeeze out some
precip before this given the amount of moisture and forcing
beginning to move into the area. Also, precip intensity may allow
precip to initially fall as very wet snow for a couple hours over
Nrn Lower this evening before switching over to rain. Precip marches
to the northeast through the evening, reaching E. Upper as snow by 9
or 10pm. (One caveat here is the assumption the current snow band
moving northeast through Wisconsin doesn`t stretch over to Ern Upper
before this.) Another big question is how much evening/early
overnight lows drop before warmer air moves in. Most recent guidance
shows the interior portions of Nrn Lower hovering either right at or
a degree above freezing for a brief time around 00z. Thus a brief
period of freezing rain is possible in the higher terrain this
evening. Ern Upper is a different story with temperatures hovering
at the freezing mark throughout much of the night, with most of the
precip tonight expected to fall as a slushy wet snow. A tight
gradient may arise (in temperature and precip types) through central
Chip/Mack counties as warm air surges northward late night/early
Saturday morning, changing precip over to rain/freezing rain.
Otherwise, still expected snow amounts of generally one or two
inches for Nrn Lower (locally higher right at the tip of the mitt
potentially). Chip/Mack counties can expect 3 to 6 inches with the
highest totals in far western portions of these counties.
&&
.SHORT TERM...(Saturday through Monday)
Issued at 336 PM EST Fri Dec 10 2021
...Very windy Saturday with mixed precip...
High Impact Weather Potential...High. Winter storm conditions
continue in parts of eastern upper MI Sat. Very windy.
A rapidly deepening surface low will lift across northern lower MI
Sat morning, a few hours slower than it appeared yesterday. A dry
slot will scoot quickly eastward across northern lower MI in the
morning, with wraparound/deformation precip continuing in
central/eastern upper MI and pushing back into northern lower MI.
But this will all exit to the ne fairly abruptly late in the
afternoon into the evening. Precip and wind trends are the primary
concerns.
Morning starts out with a dry slot over much of northern lower, on
up into Drummond Isl. Leftover synoptic precip may still linger in
the far se. But wraparound/deformation will be continuing over
central/eastern upper MI, and will wrap back into nw lower. Precip
will continue thru midday, then gradually diminish and end in the
afternoon and early evening. A bit of lake enhancement will develop
on the tail end of synoptic precip, with 850mb temps quickly
lowering to -8/-9C. Initially, most areas will be just rain, with
wintry precip (FZRA and snow) in the west half of Chip/Mack Cos.
Colder air will make more abrupt inroads beginning mid morning, with
precip mixing with and turning to snow before ending. Mixed precip
will linger along the nw lower MI coastline all day long, even while
the higher elevations inland will have turned back to all snow.
Highest snowfall amounts will be in far western Chip/Mack Cos, with
2-4" west of a Bay Mills-Epoufette line. In northern lower MI, 1-2"
accums occur in the higher terrain snowbelts from Kalkaska to GLR.
Lesser snow amounts elsewhere.
High winds will arguably be a bigger story than wintry precip. An
initial surge of isallobaric post-frontal sw winds arrives in the
morning. The highest winds with this will be largely downstate,
though the plume of strongest winds eventually spreads into our se
zones, especially along Saginaw Bay. A wind shift to nw occurs
midday into the afternoon, and these will be quite gusty across all
of northern MI. Gusts of 40-45mph will be common from midday into
very early evening. Will be issuing wind advisories for essentially
all of the northern lower MI coastline (excluding Gd Trav Co,
including Beaver Isl). Gusts to or in excess of 45mph will be most
confidently felt here. Things are more marginal inland; in addition,
the combination of snow and winds might make winter wx advisories a
better choice of headline in some interior counties. Will decline to
issue anything for these areas at this time, but additional
wind/winter headlines are a distinct possibility for Saturday.
Sunrise temps will range from the lower 30s in western Chip/Mack, to
the mid 40s near Saginaw Bay. Temps will be in the 30-35f range by
early evening.
Much quieter wx for the rest of the short term. Fastest 500mb
westerlies migrate north into Canada, with 500mb heights steadily
building across the central/eastern CONUS. Sprawling high pressure
covers the OH/TN Valleys and mid Atlantic states, ushering in mild
Pacific air. Dry and mild wx is in the offing Sunday into Monday.
Max temps will be mainly near 40f to the mid 40s both days. Mostly
sunny skies Sunday, with a bit more cloud cover Monday (especially
north of M-32.
.LONG TERM...(Monday night through Friday)
Issued at 336 PM EST Fri Dec 10 2021
...Unseasonably warm midweek...
High Impact Weather Potential...Minimal.
Unseasonably mild Pacific air will cover the region most of next
week. The faster 500mb flow will remain north of the area, as 500mb
ridging will be overhead by Wed morning. Energy eventually ejects
from the sw states, displacing the ridge and returning precip and
cooler temps to the area. Rain showers are likely by late Wed, and a
rain-snow mix is possible by late Thursday as cooler air filters
back in. We could well flirt with record high temps at all sites on
Wednesday, when northern lower MI looks to be in the 50s, and
eastern upper MI upper 40s to around 50f.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 625 PM EST Fri Dec 10 2021
Conditions expected to deteriorate to IFR overnight into Saturday
morning as band of rain and br/fg overspread the area from the
southwest. May see precipitation begin as a wintry mix initially
overnight, perhaps bringing some minor snow accumulations. Rain
transitions back to snow on Saturday, once again likely bringing
some minor accumulations. Band of wind shear tonight gives way to
very gusty northwest winds on Saturday, with gusts likely
exceeding 35 knots during the afternoon. Cigs will rise/scatter
out heading toward later Saturday afternoon.
&&
.MARINE...
Issued at 336 PM EST Fri Dec 10 2021
Strong low pressure will move ne across northern lower MI Sat
morning. Southerly winds ahead of the low will veer sw early Sat,
and then nw midday into the afternoon. Those winds will be very
strong Saturday, with at least gales on all waters. Have upgraded
the waters either side of Presque Isle Lt on Lk Huron to storm
warnings for a short period Sat afternoon, where gusts to circa 50kt
are likely in an area of favorable coastal convergence. Winds will
weaken Sat night.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY from 10 AM to 8 PM EST Saturday for MIZ016>018-
020>036-041-042-098-099.
WINTER STORM WARNING until 4 PM EST Saturday for MIZ086-087.
WINTER WEATHER ADVISORY until 4 PM EST Saturday for MIZ095-096.
LH...GALE WARNING from 9 AM to 9 PM EST Saturday for LHZ345-346.
STORM WARNING from 9 AM to 8 PM EST Saturday for LHZ349.
STORM WARNING from 3 PM to 8 PM EST Saturday for LHZ347-348.
LM...GALE WARNING from 9 AM to 9 PM EST Saturday for LMZ323-341-342-
344>346.
LS...GALE WARNING from 9 AM to 9 PM EST Saturday for LSZ321-322.
&&
$$
UPDATE...MB
NEAR TERM...STJ
SHORT TERM...JZ
LONG TERM...JZ
AVIATION...MB
MARINE...JZ
Area Forecast Discussion
National Weather Service La Crosse WI
844 PM CST Fri Dec 10 2021
.UPDATE...
Issued at 839 PM CST Fri Dec 10 2021
Continued assessment and extrapolation of the deformation zone
arcing out of the Mid-Missouri River valley has increased
confidence just enough to lower the already marginal warning-level
snowfall totals for a few counties. Thus, have transitioned the
warning to an advisory for four counties, including La Crosse. The
gradient in the snowfall axis will still be tight and bifurcate
these counties. Cannot 100 percent rule out some 6 inch snowfall
reports in the northern portions of these counties, but the vast
majority of the population should see less than 6 inches and have
adjusted the headlines accordingly. The impacts, nonetheless, will
change little. Expect slippery roads through the night,
especially with freezing rain mixing in at times across the
advisory.
UPDATE Issued at 607 PM CST Fri Dec 10 2021
Given the trends in radar/satellite/CAMS, have pulled forward the
end time of the eastern warning/advisory from noon to 9am. Also
have blended in more HRRR QPF to the near-term QPF fields to
tighten the southern end of the snow band. La Crosse remains
situated on the very edge of the snow band, thus snowfall amounts
remain the most uncertain through this belt.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 220 PM CST Fri Dec 10 2021
In the overall big picture, not a lot has changed with the winter
storm. Water vapor satellite shows the upper level system is
coming across the central Rockies with a nice baroclinic leaf
forming out ahead of. This wave will continue to track northeast,
coming across with a positive tilt during the overnight hours.
This looks to produce a period of moderate to strong pv advection
in the 500 to 300 mb layer. There also looks to be a period of
some decent jet dynamics late this afternoon into the evening with
the area coming under the right entrance region of a departing
300 mb jet and the left exit region of the next incoming jet
streak.
The first band of mid-level frontogenesis has come in and
produced the first round of light snow across southeast Minnesota
into western Wisconsin. This frontogenesis will continue to work
on the atmosphere as it lift off to the northeast through the rest
of the afternoon. It will quickly be replaced by another band
which looks to be stronger and not quite as migratory as the
first. The lift from this band will be augmented by the jet
dynamics, increasing pv advection ahead of the wave and good
isentropic up glide on the 285K surface. This all looks to combine
to produce the period of highest snowfall rates from late this
afternoon through much of this evening. The 11.12Z HREF continues
to show a strong signal for hourly snowfall rates in excess of 1
inch with a signal for some 2 inch an hour rates as well. This
signal has shifted northwest from this time Thursday with it now
looking to be along our forecast border with MPX or just into
their area. The 2 inch per hour rate signal does look to be almost
all into MPX`s area at this time. This looks to have shifted the
highest band of snowfall amounts just a little farther northwest.
Farther to the south, with the slight northward shift, the warm
nose aloft looks to have more an influence over our southeast
counties to create more of wintry mix than just snow. Based on the
thermal profiles depicted in the RAP forecast soundings, a period
of sleet and freezing rain or rain (depending of surface
temperatures) will occur along with some snow. Some ice
accumulations could occur with the highest probabilities for these
being from northern Richland County into the southern sections of
Adams and Juneau Counties. Amounts should be just a glaze to less
than a tenth of an inch.
The final hazard from this system will occur overnight. Another
band of frontogenesis will occur, although this does not look to
be a strong or as big in areal coverage, but enough to produce a
burst of snow. This will likely occur as the winds are swinging
around to the northwest on the back side of the surface low with
gusts up to 35 mph possible. This will be enough to move some of
the fresh snow around to create drifting and some pockets of
visibility reductions from blowing snow. Everything looks to wind
down pretty quick Saturday morning as the system pulls away from
the region.
At this time, no additional changes are planned to the layout of
warning and advisory. Some of the counties on the southern edge of
the border may not get all the way to six inches, but when
combined with the wind and blowing/drifting potential, enough
impacts to justify not making any more adjustments.
.LONG TERM...(Saturday night through Friday)
Issued at 220 PM CST Fri Dec 10 2021
Just taking a cursory glance out into next week shows that
another system looks to move across the Upper Midwest sometime in
the middle of the week. Starting to see some differences now
between the models on the timing and potential strength of this
system. Most models continue to show the area getting into the
warm sector of this storm with the 10.00Z NAEFS still showing the
specific humidity and precipitable water running 4 to 5 standard
deviations above normal. Plenty of warm air coming in as well,
with temperatures at 925 and 850 mb having the potential to be
about 2 standard deviations above normal. This should help to push
high temperatures Wednesday into the 50s and maybe even some
lower 60s possible for portions of northeast Iowa into southwest
Wisconsin.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 607 PM CST Fri Dec 10 2021
Widespread aviation impacts continue tonight due to heavy snow and
a wintry mix over much of the area. Expect widespread IFR to LIFR
conditions through the overnight hours, improving from west to
east between 09-15Z. Gusty northeast winds back to the northwest
late and then continue backing to the WSW by midday on Saturday.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 9 AM CST Saturday for WIZ041>044-
053>055.
Winter Storm Warning until 6 AM CST Saturday for WIZ032.
Winter Storm Warning until 9 AM CST Saturday for WIZ017-029-033-
034.
MN...Winter Weather Advisory until 6 AM CST Saturday for MNZ096.
Winter Storm Warning until 6 AM CST Saturday for MNZ079-086>088-
094-095.
IA...Winter Weather Advisory until 6 AM CST Saturday for IAZ009>011-
018-019-029-030.
Winter Storm Warning until 6 AM CST Saturday for IAZ008.
&&
$$
UPDATE...Skow
SHORT TERM...04
LONG TERM...04
AVIATION...Skow
Area Forecast Discussion
National Weather Service Denver/Boulder CO
847 PM MST Fri Dec 10 2021
.UPDATE...
Issued at 846 PM MST Fri Dec 10 2021
A few snow showers are still ongoing in the mountains but in the
majority of areas the snow has stopped. There will be some blowing
and drifting snow tonight across the higher mountain passes as the
winds increase. It will take a few hours for the stability to
increase over the mountains but after midnight, a strong mountain
wave will develop with wind gusts up to 75 mph in the foothills.
The highest winds will occur during Saturday night with the best
flow aloft and the development of a mean state critical layer.
Otherwise, it will be a very chilly night with wind chills below
zero across much of the forecast area.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 158 PM MST Fri Dec 10 2021
RAP mesoanalysis and water vapor satellite indicate that the
current trough axis is located over northeastern Colorado and is
continuing to lift to the northeast. Gusty winds have developed
this afternoon with strong northwesterly flow aloft, with a few
gusts into the 45-50 mph range noted over the eastern Plains.
While it hasn`t been as windy for the Denver metro, winds are
slowly picking up, and there should be a brief window of 30-45 mph
gusts as subsidence on the backside of the trough helps push some
of these stronger gusts to the surface. Across the mountains,
light orographic snow continues, particularly over the Park Range.
Light snow will gradually taper off this evening and overnight,
with just a couple of additional inches expected. With diminishing
snow, we`ll allow the Warnings/Advisories to expire at 5pm this
evening.
Tonight will be mostly quiet and cold across the plains and urban
corridor, with lows dropping into the low 10s to single digits.
The usual cold spots like Limon could fall to near 0. Over the
mountains, strong winds are likely to develop tonight as a
mountain wave develops. Sangster forecasts are bullish with the
win potential through Saturday night, though deterministic
guidance shows more of a marginal event. The current forecast
leans more towards the ingredients based approach and calls for
warning-criteria gusts beginning tonight. We may see an initial
burst of stronger gusts late this evening/early tonight
corresponding to the mid- level subsidence crossing through the
area, and thus we`ve pulled the High Wind Warning start time up to
midnight tonight. Gusty winds should continue into Saturday
evening.
Otherwise, tomorrow will be quieter for most of the forecast area
as zonal flow develops and temperatures warm up a bit. Highs
should reach the 40s over the plains with 20s to 30s common for
the high valleys. Outside our typical mountain wave clouds it
should be a mostly sunny start to the weekend.
.LONG TERM...(Saturday night through Friday)
Issued at 158 PM MST Fri Dec 10 2021
On Saturday night a good bet of high winds continuing into Sunday
morning for the mountains and Front Range foothills. Cross sections
showing 40-65kt cross barrier flow along with mountain top stable
layer resulting in a modest profile for an amplified mountain wave.
In addition...hefty progged surface gradient of 13-17mb across the
state through this period with local high wind program in the warning
category. High resolution models showing peak winds in the 50-70kt
range. Considering the above parameters will upgrade the high wind
watch to a warning and will extend it further in time through Sunday
morning. High resolution models (HRRR/WRF) showing peak winds
60-75kt range.
For the later Sunday through Tuesday time frame; expect a return
to dry conditions along with a warming trend through the period.
The flow aloft will shift more southwest for Monday and Tuesday
with temperatures bouncing back into the upper 50s/60s across the
plains.
The next significant system is expected to pass across Colorado
sometime in the Tuesday night through Wednesday night time frame.
There is some timing and amplitude differences amongst the models
with the Euro/Canadian runs faster with less amplitude than the GFS.
There is a chance of snow with this system, especially in the
mountains but the bigger potential may be the wind. Especially given
the GFS scenario with an ejecting closed upper low moving to the
northeast across the state and deepening across Nebraska. QG omega
fields showing very strong downward forcing of 40-60mb/hr rises
while cross sections showing 50-65kt of cross barrier flow
developing as the low kicks out northeast. Still positioning and
amplification still in question so overall wind strengths will be
quite varied depending on low positioning.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 846 PM MST Fri Dec 10 2021
VFR conditions expected throughout the TAF period. Moderate
westerly winds are expected to weaken and turn towards drainage in
a couple hours at DEN and APA. Winds will be light during the day
tomorrow. As for BJC, there will be sporadic gusts up to 35 knots
possible throughout almost the entire TAF period. Stronger winds
will come and go.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from midnight tonight to noon MST Sunday for
COZ033>036.
&&
$$
UPDATE...Danielson
SHORT TERM...Hiris
LONG TERM...Entrekin
AVIATION...Danielson
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
1001 PM CST Fri Dec 10 2021
.DISCUSSION...
Pacific front/dryline was near the northern Hill Country while the
strong cold front was diving south over northwest Texas. Front
still on pace to reach south Texas during the overnight hours.
Colder air and stronger winds will arrive after daybreak Saturday.
Adjusted temperatures to show non-diurnal trend behind the front.
Scattered convection still possible over the coastal plains as
the front moves through early Saturday morning. No changes with
the current PoPs forecast.
Elevated fire danger conditions will be possible over the Brush
Country to the Coastal Bend as drier air and gusty winds linger
over the region Saturday afternoon.
&&
.MARINE...Moderate to strong south winds and elevated seas will
continue over the offshore waters until 06Z. Timing of cold front
still on track to move into coastal waters around 13Z with winds
increasing to very strong with gusts to gale force after 16Z.
Kept Gale Watch in place and let night shift make to decision
to upgrade. May be able to keep the bays out of Gale Warning. No
changes were made to PoP forecast with convection increasing with
the cold front.
&&
.PREV DISCUSSION... /Issued 555 PM CST Fri Dec 10 2021/
AVIATION...00Z TAFs
Winds will diminish early this evening as the low level jet moves
off to the east with the trough/dryline moving toward the region.
Shallow moist layer will remain over the coastal plains in
advance of the boundary. MVFR ceilings have persisted in the VCT
area and expect will continue this evening. Stratus will develop
over the Coastal Bend by 06Z with fog forming over the inland
coastal plains as winds diminish. Expect MVFR vsbys will be
prevalent but there could be IFR vsbys periodically until the
winds shift. Expect the initial wind shift to reach COT by 07Z and
CRP by 13Z. Stronger winds with the arrival of the cold air will
occur around 15Z Saturday with winds gusting to near 30 knots
over the coastal plains. There will be a brief period along and
behind the front when showers (possibly a thunderstorm) could
occur over the coastal plains. Then conditions will improve to VFR
with ceilings around 5 kft lingering over the coastal plains
through the afternoon.
PREV DISCUSSION... /Issued 354 PM CST Fri Dec 10 2021/
SHORT TERM (Tonight through Saturday Night)...
Big changes tonight and Saturday as a strong cold front moves across
S TX. The cold front is currently moving south into the TX Pan
Handle while a dryline is moving east across W and Central TX. The
cold front is expected to surge south and southeast through the
evening and is expected to reach the northwest portions of the CWA
close to midnight. Models have been consistent in bringing a
southwest to northeast oriented frontal boundary through S TX
overnight, reaching Laredo and Victoria between 07Z to 10Z. The
boundary is progged to reach the southern Coastal Bend between 10Z-
14Z. As the boundary approaches VCT, showers and a few thunderstorms
are forecast to develop ahead and along the boundary, then more
thunderstorms are expected to develop and spread southeastward with
the front. The best chance for thunderstorms will be along the coast
and over the gulf waters where moisture is deepest and instability
is strongest. Models prog the strong capping inversion in place
across S TX to diminish along the cold front. Moderate CAPE values
around 1300J/kg across the Coastal Bend up to around 2400J/kg across
the gulf waters are progged for tonight. Strong low level moisture
convergence with the frontal boundary combined with increasing
diffluence aloft as a strong upper jet sinks south and places the
RRQ of the jet over S TX, will contribute to deeper convection. The
combination of these features will be conducive for some storms to
become strong along the coastal areas and across coastal waters.
Gusts to around 40 mph are possible across the Coastal Bend. As the
line moves across the coastal waters, gusts may reach 40-45 knots.
The inhibiting factor will be just how quickly the cap weakens.
Behind the cold front on Saturday, strong gusty north winds will
develop and bring drier and cooler conditions into the area through
the day. Could see the high temperature in the morning with falling
temps during the afternoon. The Rap and HRRR show light precip
behind the cold front with mid level clouds remaining across the
area. This looks reasonable given that the main upper trough will be
working its way across the region. Am expecting that any precip that
does fall will likely be virga due to dry low levels.
Skies finally clear out from northwest to southeast Sat night along
with diminishing winds. This will enhance radiational cooling with
lows expected to dip down into the upper 30s across the northern CWA
to upper 40s along the coast and low 50s across the islands.
LONG TERM (Sunday through Friday)...
High pressure builds over the area Sunday and remains in place for
the long term period. Onshore flow bringing increased moisture with
PWAT`s around 1.40-1.50" combined with a developing coastal trough
will increase chances for showers and thunderstorms Monday into
Tuesday. Then on Wednesday a mid-level low over the Desert SW will
slide off to the north east but not expecting a cold front to reach
South Texas despite model discrepancy with this feature. Currently
have slight PoPs extending from offshore inland over the Victoria
Crossroads area, Thursday through Friday due to some isentropic
lifting.
Temperatures are expected to start the week in the 60s and warm back
to the low to mid 80s for the week with lows near 50 also warming to
the mid 60s.
MARINE...
Winds are expected to decrease to more moderate levels tonight with
advisory conditions diminishing by midnight as a cold front
approaches the region. Foggy conditions will be possible once again
tonight over the bays and nearshore waters ahead of the advancing
boundary. The cold front will be moving through the area early
Saturday morning creating a strong to very strong offshore flow
through the day. Frequent gusts to gale force are expected and a
Gale Watch is in effect for Saturday across the bays and coastal
waters. Scattered showers and thunderstorms will be possible late
tonight, becoming numerous early Saturday morning as the front moves
across the waters. Strong offshore flow will continue Saturday
evening, with gusts to gale force expected. Conditions will
improve late Saturday night and Sunday. Moderate northeast flow
on Sunday will turn to onshore flow Monday and become weak to
moderate. This flow will continue into the week. Isolated showers
and thunderstorms will be possible Monday and Tuesday as a coastal
trough develops along the Middle Texas Coast.
&&
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 67 69 45 66 55 / 30 30 0 0 10
Victoria 60 62 39 65 49 / 50 10 0 0 10
Laredo 66 70 43 70 53 / 10 10 0 0 0
Alice 66 69 40 69 51 / 20 20 0 0 10
Rockport 64 68 43 66 57 / 50 50 0 0 10
Cotulla 61 66 40 71 49 / 0 0 0 0 0
Kingsville 69 70 44 67 53 / 30 30 0 0 10
Navy Corpus 68 69 51 67 60 / 40 60 0 0 10
&&
.CRP WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Gale Watch from Saturday morning through Saturday evening For
the following zones: Bays and Waterways from Baffin Bay to
Port Aransas...Bays and Waterways from Port Aransas to Port
O`Connor...Coastal waters from Baffin Bay to Port Aransas
out 20 NM...Coastal waters from Port Aransas to Matagorda
Ship Channel out 20 NM...Waters from Baffin Bay to Port
Aransas from 20 to 60 NM...Waters from Port Aransas to
Matagorda Ship Channel from 20 to 60 NM.
Small Craft Advisory until midnight CST tonight For the
following zones: Waters from Baffin Bay to Port Aransas
from 20 to 60 NM...Waters from Port Aransas to Matagorda
Ship Channel from 20 to 60 NM.
&&
$$
TMT/89...SHORT TERM
Area Forecast Discussion
National Weather Service Des Moines IA
929 PM CST Fri Dec 10 2021
...Updated for Near Term Weather Trends...
.UPDATE...
Issued at 929 PM CST Fri Dec 10 2021
No changes planned to the current warning and advisory. The
deformation band of snow from Lincoln through our northwestern
forecast area and up toward the Twin Cities is being aided by
700mb frontogenesis, which shows up well on the latest SPC
mesoanalysis. RAP cross section along this shows the moderate lift
with saturation through much of the dendritic growth zone. This
lift will wane from southwest to northeast over the next 6 hours
or so and the accumulating snow will be done by daybreak
Saturday. Forecast has continued a slight northward shift with the
snowfall amounts to better line up with the path of the
deformation zone. Thus, blended in some HRRR time lagged QPF
earlier this evening to lower snow totals slightly, but not
greatly enough to change any headlines. With surface low pressure
over southeastern Iowa now, winds across central Iowa are from
the north or northwest and increasing. Gusts nearing 40 mph are
occurring at EST with 25 to 35 mph gusts more common at this point
across northern Iowa. Of course, these winds with falling snow
will reduce visibility. Farther south, have also been monitoring
visibility reduction under a mile due to areas of fog. Issued an
SPS earlier this evening that will end shortly over south central
Iowa and with winds increasing should also see visibilities come
up above a mile.
Lastly, have been monitoring the drizzle and near freezing
temperatures here in the metro and points west. Concern has been for
freezing drizzle with air temperatures near or just below freezing,
but with road conditions from Iowa DOT ranging from 32F at Adair to
the mid-30s in the Des Moines metro have not seen this materialize
so far.
&&
.DISCUSSION.../Tonight through Friday/
Issued at 325 PM CST Fri Dec 10 2021
Key Messages:
-Significant winter storm impacting portions of the forecast area
through daybreak on Saturday.
-Dry and much warmer into early next week with possible record
warmth by midweek.
Surface low is currently across eastern Kansas and is continuing to
deepen. Warm front across Missouri is surging northward in advance
of the low and is approaching southern Iowa late this afternoon. It
is likely to advance into the southeast prior to the surface low
arriving. Therefore, temperatures are likely to continue to rise in
the southeast late this afternoon and early evening prior to the
arrival of the low. Visibilities have also fallen as dewpoints have
continued to climb into the mid 40s and these reduced visibilities
are likely to persist until the low passes this evening. In
addition, some instability is likely to clip the southeast corner of
the forecast area and have included a brief few hours of thunder
when the low passes. The storms may also produce some small hail
but the threat of severe weather likley passes just southeast of the
area. Otherwise, cold advection is increasing in the northwest and
this begins to overspread the area as the evening continues and the
surface low moves into northern Iowa. Snow is expected to persist
across the far northwest into tonight with the deformation zone
eventually push east into the rest of central Iowa overnight. There
may be some light drizzle or even freezing drizzle prior to the
arrival of the deformation zone in central and southern portions of
the state this evening but should transition to snow the column
saturates. Overall amounts appear somewhat lighter with totals of 7
or 8 inches in the far northwest near EST to an inch in the southern
portion of the advisory area. Winds become more north to northwest
overnight and quite strong at 15 to 25 mph with gusts of over 30 mph
at times. This will lead to poor visibilities, especially in areas
that have over 2-3 inches of snow on the ground. At this time,
blizzard conditions may occur briefly in the north, but a sustained
period is not expected at this time and have left all headlines "As
Is" at this point. The precipitation is expected to end around
daybreak on Saturday as the system departs with the wind slowly
diminishing through the day as the sun returns to most locations.
Guidance continues to indicate a broad upper ridge developing across
the central United States during the second half of the weekend into
the middle of next week. This allows warm air to spread into the
state as thermal ridging develops across the Plains. It remains
plausible for record highs on Tuesday into Wednesday next week with
Wednesday being the warmest day. Otherwise, a shortwave in the
southwest US ejects rapidly into the Midwest later Wednesday into
Wednesday night with associated surface boundary passing through the
state during this time. Instability remains evident in guidance
across the state by Wednesday afternoon, therefore the timing of the
boundary through Iowa the possibility of convection at a given
locations. Otherwise, cooler air arrives through the end of the
work week but with readings still above normal for this time of
year.
&&
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 547 PM CST Fri Dec 10 2021
Nearly all reporting sites across central Iowa are IFR or LIFR
and these conditions will prevail overnight as winds from the
northeast early this evening rotate counter-clockwise and become
from the northwest as they increase overnight. Snow will continue
much of the night at MCW and FOD with blowing snow possible as the
winds increase. A transition from drizzle or light rain to snow
is expected at ALO and DSM near or after midnight. While it is low
confidence and not included in the official TAFs, a short period
of light freezing drizzle is possible at both sites dependent on
liquid precipitation occurring as air and surface temperatures
fall this evening. Conditions will improve into VFR Saturday
morning with brisk winds from the northwest persisting through the
day.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST Saturday for IAZ039-049-
050.
Winter Storm Warning until 6 AM CST Saturday for IAZ004>007-
015>017-023.
Winter Weather Advisory until 6 AM CST Saturday for IAZ024>028-
033>038-044>048.
&&
$$
UPDATE...Ansorge
DISCUSSION...Cogil
AVIATION...Ansorge
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
704 PM CST Fri Dec 10 2021
.UPDATE...
At 7PM the cold front was moving south through the Panhandle. A dry
line extended from near Fort Worth all the way southwest to near
Rocksprings and Del Rio. The cold front is forecast to accelerate
southward late this evening moving through the CWA overnight, with a
pre-frontal wind shift ahead of it. Latest HRRR runs still depict a
broken, thin line of convection developing from just east of Austin
south to near Seguin between midnight and 2AM, then quickly moving
southeast into the Coastal Plains between 2AM and 5AM.
Windy behind the front through the morning and into the early
afternoon on Saturday, with some gusts up to 35 mph. Appears
sustained winds will stay just below Wind Advisory criteria.
Wind speeds gradually weaken late afternoon the fall off quickly
after sunset and with cirrus shield exiting east this should setup
good radiational cooling night. We have lowered low temperatures
Sunday morning slightly, a blend of the previous forecast and the NBM
25th percentile. This will place all of the Hill Country in a freeze
and potentially some drainage areas just south of U.S. 90 as well as
east of I-35. A Freeze Warning is likely coming for the Hill Country
by tomorrow.
&&
.PREV DISCUSSION... /ISSUED 534 PM CST Fri Dec 10 2021/
AVIATION (00Z TAFs)...
VFR conditions prevail across South Central Texas this evening.
Guidance indicates MVFR ceilings may try and develop just east of an
AUS-HYI-BAZ line 04Z-06Z, before being swept eastward overnight with
the pre-frontal wind shift and cold front. Convective allowing models
still indicate the possibility of a broken and thin line of convection
developing east of I-35 and I-37 between 06Z-10Z. At this time it
looks like SHRAs and TSRAs will remain east of AUS/SAT/SSF.
Gusty north winds develop behind the cold front overnight and
persist through the morning and early afternoon Saturday, then
gradually weaken late afternoon. Wind gusts between 25-30KT are
forecast in many areas.
PREV DISCUSSION... /ISSUED 213 PM CST Fri Dec 10 2021/
SHORT TERM (Tonight through Saturday Night)...
Skies have cleared out for the most part with just some scattered to
clouds in the eastern half of the area as southwest flow prevails at
the surface. This southwest flow will lead to an unseasonably warm
today with possible record highs across the area. Temperatures are
already into the middle 80s in some locations. A strong upper trough
is passing through the Central Plains with the surface low in
northeastern Oklahoma. As the system moves east, there should be a
wind shift from the northwest that comes into the CWA this evening
ahead of the actual Canadian cold front. This feature should lead to
a thin line of showers and perhaps a thunderstorm for our eastern
counties. There is a chance of a strong storm, if the convection is
able to become rooted and sustained in the boundary layer but
overall chances of this are very low.
The actual cold front with the better drop in temperatures is
expected to move into the area after 2 AM overnight and will be
through the CWA by 8 AM. Winds behind the front during the morning
will be in the 15 to 20 mph range with higher gusts. The wind speeds
will lessen a bit as we progress through the day. This will help
keep the period of strongest winds to not line up with the period
with the lowest afternoon humidity. Therefore, think the western
areas will only see elevated to near critical fire weather
conditions, and do not think any headlines will be needed. For the
eastern areas tomorrow, some mid-level moisture and lift will move
overhead which could lead to some elevated showers, but the low-
levels will be very dry and will not mention anything in the
forecast at this time, but there should be at least some nice virga
around. Highs tomorrow will be much cooler today, or about 25
degrees cooler than today.
Winds are expected to weaken tomorrow night and skies should also
clear. This could lead to the first freeze for a decent portion of
the Hill Country, and portions of the I35 corridor away from the
city centers. If the trends in the forecast, a Freeze Warning will
likely be issued at a later time.
LONG TERM (Sunday through Friday)...
Sunday morning will start off cold with temperatures near freezing
with an extension of the surface high overhead. This high will
quickly move to the east, establishing southerly return flow across
the area. Isentropic upglide over the retreating shallow cool air
will result in cloudy skies and reduced diurnal heating on Monday,
so morning lows will be quite a bit milder, but afternoon highs near
or slightly below those on Sunday.
The southerly return flow will deepen and strengthen through the
week as another cyclone moves through the central Plains. This will
bring a climatologically familiar pattern with a warming and
moistening trend. Expect the return of morning fog and
drizzle/showers by Wednesday, then continuing into Friday. A
stalling front/boundary in the wake of the central Plains cyclone
will end up along or north of our northern border Friday night into
next Saturday, potentially bringing rain back into the area.
However, this is too far in the future for more than low chance PoPs
and relatively light QPF at this time.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 52 59 36 64 43 / - 0 0 0 0
Austin Bergstrom Intl Airport 51 60 30 64 40 / 10 0 0 0 0
New Braunfels Muni Airport 53 61 33 65 42 / 10 0 0 0 0
Burnet Muni Airport 48 57 31 64 42 / 0 0 0 0 0
Del Rio Intl Airport 55 66 38 67 44 / - 0 0 0 0
Georgetown Muni Airport 49 57 31 63 41 / - 0 0 0 0
Hondo Muni Airport 54 63 32 66 42 / - 0 0 0 0
San Marcos Muni Airport 52 60 32 64 41 / 10 0 0 0 0
La Grange - Fayette Regional 54 61 35 65 45 / 40 - 0 0 0
San Antonio Intl Airport 55 61 35 64 46 / - 0 0 0 0
Stinson Muni Airport 57 64 37 67 46 / - 0 0 0 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term/Aviation...76
Long-Term...Brady
Area Forecast Discussion
National Weather Service Grand Rapids MI
1025 PM EST Fri Dec 10 2021
LATEST UPDATE...
Update/Marine
.UPDATE...
Issued at 1023 PM EST Fri Dec 10 2021
Main concern tonight is the wind, but it is not the only concern.
We considered upgrading to a High Wind Warning across portions of
our area for Saturday, but in the end decided to hold off based
on coordination and the latest guidance coming in. The 18Z 3km
NAM was more bullish on winds reaching warning criteria, but the
00Z came in and backed off just a bit. It may have just nudged
the winds south into the I-94 corridor. The HRRR remains fairly
close to warning criteria gusts with each run. The area of most
concern in the HRRR stretches from Grand Haven/Holland/South Haven
northeast towards Mt.Pleasant/Lansing/Alma (essentially the heart
of the forecast area). The HRRR is trying to indicate gusts in
this area around 55 mph if not 60 mph. Bottom line the overnight
shift will be looking into whether or not we need to upgrade
anywhere. We did add the remainder of the CWA into the Wind
Advisory, namely the counties that were not in the headline up
along U.S. 10 across Central Lower Michigan.
Most of the models are in the advisory range when it comes to the
wind gusts, but its the higher resolution models that are the ones
flirting with warning criteria. The message is certainly out that
we are expecting high winds tomorrow. The winds will come up
suddenly out of the southwest between 700 AM and 1000 AM on
Saturday morning. The high winds will continue all day, backing
off Saturday evening.
We are still expecting the threat of thunderstorms tonight into
Saturday morning. The highest MUCAPE values in the 500-1000 j/kg
range nose up into our area between 100am and 1000am. Cannot rule
out a few higher end gusts given the winds that are present in the
profile.
&&
.DISCUSSION...(This evening through next Friday)
Issued at 300 PM EST Fri Dec 10 2021
- Wind Advisory for much of the CWA later tonight through Saturday
Ensemble model trends have shown a lowering of the max wind gusts
for this system tonight into Saturday. At this time only low
confidence exists for a high wind warning event. That being
said...this is a very anomalous event with intense winds showing
up around 500 mb...topping 120kts 15z to 18z Saturday. Cross
sections still show a trop fold event is likely to occur which
could help this system reach a greater magnitude of impacts. This
system will be strengthening on top of us...which will also result
in some uncertainty as to the overall impact. We are going to
start the headline up around 05z. We used this earlier time to
account for the potential for high gusts with the bands of showers
and storms that will be starting to move in then. Several models
are showing 60 knots or higher winds not too far off the ground.
With SPC showing a marginal day 1 risk for southern parts of the
CWA...it is possible that severe thunderstorm warnings could cover
any short duration severe convective wind gusts. Either
way...scattered power outages are expected with numerous outages
still possible for later tonight through much of Saturday.
- Period of snow Saturday afternoon/evening
As the storm pulls away from the CWA the wrap around moist will be
drawn in from the west. Temperatures will drop off quickly changing
the rain to snow late in the morning into the afternoon. Models are
showing the potential for 1 to 3 inches of snow. Road temperatures
will be wet and relatively warm to start with the bulk of the
accumulations expected on colder surfaces. It may struggle for
surface temperatures to fall below freezing before the snow ends.
For now we are not highlighting winter impacts with this system.
- Considerable warmup for next week
Deep warm air advection moves in for mid week. Temps at 850 mb
are shown to climb above 10 deg C with 925 mb temps into the
teens. It looks likely that temps will climb through the 50s and
perhaps into the 60s. One limiting factor for how warm it gets could
be the low clouds. RH forecasts for 925 mb show a surge of
moisture lifting up from the Gulf and into MI then. The low cloud
cover would limit the mixing heights and ultimately the max
temperatures for the day. Just from advection alone
though...well above normal temperatures are predicted.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 718 PM EST Fri Dec 10 2021
Significant winds expected at all TAF sites on Saturday. Winds
will be strong for night time hours tonight as they veer from
southeast to south-southwest. Tonight`s winds will be of the 15-30
knot variety. A stark and sudden increase in wind will be noted
across the entire area between 700am and 930am Saturday morning.
The strong winds will first be seen down towards BEH around 700am
and then sweep north and east through LAN and JXN around 900am.
Winds will increase to 20-30 knots out of the southwest with gusts
into the 40-50 knot range. Wind gusts over 40 knots will be
common all day on Saturday, with peak gusts nudging up towards 50
knots. Winds will shift from the southwest Saturday morning to
more of a westerly direction Saturday afternoon, so north/south
runways will have a significant cross wind.
As for other aviation conditions, they will be equally as poor.
Ceilings are in the process of dropping to the IFR and LIFR
categories as of 700pm. These low ceilings will remain in place
through roughly 100am. There may be some lifting of the lower
ceilings across the southern TAF sites along I-94, but at best an
improvement to only MVFR is expected. IFR and MVFR ceilings will
be present most of Saturday with a rapid improvement to VFR
towards 700pm.
Rain showers will move through the area this evening, followed by
scattered showers and possibly thunderstorms overnight.
Precipitation will become mixed with and change over to snow
during the late morning and early afternoon hours of Saturday.
Bottom line...less than ideal conditions expected the next 24
hours with low ceilings and visibilities tonight, along with a
chance for some thunderstorms, followed by significant wind on
Saturday.
&&
.MARINE...
Issued at 1023 PM EST Fri Dec 10 2021
Maintained the Small Craft Advisory through 500 AM and the Gale
Warning thereafter. Big Sable Point is already flirting with 30
knot gusts. Winds will ramp up significantly over the lake late
tonight and continue throughout the day on Saturday. Solid high
end gales to 45 knots are expected through the day on Saturday.
The winds will be strong all day, not falling below gale force
until into the evening hours, near or slightly after 700 PM. Could
see the gale needing to be extended through 1000 PM Saturday
evening.
In terms of the waves, 10-15 foot waves look likely in most
nearshore zones, which is typical of a high end gale. Highest
waves per a local model run based on HRRR winds would be near
Grand Haven towards sunset, in excess of 15 feet. It still appears
lakeshore flooding issues should not materialize given the lower
water levels. The FVCOM model is indicating water levels reaching
the 580-581 range. Flooding issues starting above 582.50 feet. So,
while there will likely be moderate beach erosion, flooding should
not be a big concern.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory until 7 PM EST Saturday for MIZ037>040-043>046-
050>052-056>059-064>067-071>074.
LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849.
Gale Warning from 5 AM to 7 PM EST Saturday for LMZ844>849.
&&
$$
UPDATE...Duke
DISCUSSION...MJS
AVIATION...Duke
MARINE...Duke
Area Forecast Discussion
National Weather Service Huntsville AL
813 PM CST Fri Dec 10 2021
.NEAR TERM...(Tonight)
Issued at 813 PM CST Fri Dec 10 2021
Evening soundings indicate a very volatile atmosphere in place,
although capped in our area at the moment. The combination of
significant CAPE and strong bulk shear are exceptionally strong for
this time of year over the region, especially over MS, AR, and
western TN. Supercell and tornado indices from SPC all are indicating
the potential for strong tornadoes if deep convection can develop,
especially in northwest AL into middle TN. Earlier showers in
northeast MS were not able to overcome the cap and intensify just yet
without a significant forcing mechanism. Currently, a few showers
are in northwest AL, but appear to be struggling as well. So we may
be fortunate for the next several hours. A wedge was still holding in
northeast AL where temperatures are still in the upper 50s. This
will eventually be overcome by the very warm and moist flow further
west. In contrast, KMSL was up to 73 degrees with a dew point of 68.
Successive HRRR runs indicate that convection may be held at bay for
several more hours until storms develop again in northern MS through
western TN after 06Z, moving into northwest AL after 08Z. Wind
fields may become more parallel with the line toward morning which
may slow the progress of the line east into southern middle TN and
north central AL along the I-65 corridor until after 12Z. Shear will
remain quite strong, so the threat of severe weather remains once
these arrive. So for now, really no significant changes made to the
forecast. Will maintain the Wind Advisory as well.
.SHORT TERM...(Saturday afternoon through Sunday)
Issued at 247 PM CST Fri Dec 10 2021
Behind the cold front, the severe weather threat will come to an end
by early Saturday afternoon as winds shift to the northwest. In its
wake, strong cold air advection will result in a sharp temperature
decrease as the mercury will plummet some 30-35 degrees from the mid
60s Saturday morning to the low to mid 30s by Saturday night into
early Sunday morning. Clouds will be slow to clear initially
Saturday afternoon/evening, but rapid clearing should occur by late
Saturday night into Sunday morning as a drier air mass finally pushes
in. High pressure will build into the region on Sunday, resulting in
a mostly sunny, dry, and pleasant day. Northwest winds will make it
feel quite chilly despite the sunshine with temperatures struggling
to climb above the low to mid 50s.
.LONG TERM...(Sunday night through Thursday)
Issued at 247 PM CST Fri Dec 10 2021
Tranquil weather will continue through much of the upcoming work
week as high pressure becomes established across the Deep South. Deep
southerly flow will become established under this regime, resulting
in a marked warm up as highs return to the mid to upper 60s with lows
in the upper 40s to lower 50s. Overall, very pleasant weather for mid
December with plenty of sunny, warm days to enjoy.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 439 PM CST Fri Dec 10 2021
Through most of tonight, ceilings will remain below 020agl at KMSL
and northwest AL (MVFR), and below 010agl (IFR) in southern TN and
northeast AL including. LLWS is also included as southerly flow
rapidly increases this evening into the overnight. Isolated to
scattered SHRA are possible, with perhaps a TS as well, so have kept
VCSH ahead of the main line of TS. This line arrives toward 12-13Z at
KMSL and 15-16Z at KHSV with the potential of strong to severe wind
gusts. The cold front will shift winds to the west-northwest by
16-18Z with gusts of 25-35kt possible.
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Wind Advisory until noon CST Saturday for ALZ001>010-016.
TN...Wind Advisory until noon CST Saturday for TNZ076-096-097.
&&
$$
NEAR TERM...17
SHORT TERM...AMP.24
LONG TERM...AMP.24
AVIATION...17
For more information please visit our website
at weather.gov/huntsville.
Area Forecast Discussion
National Weather Service Indianapolis IN
1012 PM EST Fri Dec 10 2021
.Forecast Update...
Issued at 1012 PM EST Fri Dec 10 2021
...Significant Severe Weather Event Ongoing/Evolving Across MS/OH
Valleys Tonight...
Rapidly strengthening low pressure is located near the
Iowa/Illinois/Missouri border as of 9 PM EST. The low will continue
to lift northeast, with a more favorable low level thermodynamic
environment advecting into central Indiana over the next few hours.
Some isolated to widely scattered prefrontal convection is currently
over the area, but mesoanalysis indicates it is likely still
elevated above a shallow stable layer, so marginally severe hail may
be the most likely severe threat in the next hour to 90 minutes with
the strongest cores that are also able to exhibit some midlevel
rotation thanks to the extreme deep layer shear values.
As the warm sector continues to expand into central Indiana,
effective deep layer shear values of 50 to 80KT and significant to
extreme low level storm relative helicity values in excess of 200-
400 m2/s2 will move into the area, along with the development of
fairly significant (especially for the time of year) surface based
instability around 500-1000 J/kg, and this will set the stage as
expected for a significant damaging wind threat and an enhanced
tornado threat as well, particularly across south central Indiana,
as the southern end of the line appears to be remaining more
supercellular at this time.
This activity to our west appears to be the main threat for central
Indiana, although some weak convective initiation appears to be
ongoing across southern Illinois just ahead of the line that could
complicate matters.
For the moment, continue to expect the prime severe window to be
through roughly 4 AM, although there remains the chance for a
secondary wind threat immediately ahead of the front a bit later in
the night. However, latest HRRR runs have been less aggressive with
development along the boundary.
&&
.Short Term...(This evening through Saturday night)
Issued at 246 PM EST Fri Dec 10 2021
Quick Overview:
--There will be a risk of severe thunderstorms, including tornadoes,
this evening and overnight, with the greatest threat roughly between
10pm and 4am.
--Impacts include; tornadoes, damaging winds (up to 80 mph
possible), and a secondary risk of hail (in most cases not exceeding
quarter size).
--This will be a nocturnal event during a time of year that
traditionally sees a low frequency of severe storms, so pre-event
messaging and emphasis of the danger of overnight storms is
important (see messaging section below).
Forecast Challenges/Uncertainties:
--Warm front position/timing, and where (how far north) specifically
the low-level thermodynamic environment will be supportive of
tornadoes.
--Whether prefrontal confluence quasi-discrete activity can evolve
into our area (conditional), or exclusively frontally-forced QLCS.
--In the best case scenario, upstream initiation of pre-frontal
discrete truly surface based convection and higher-end tornado
threat occurs mostly south of the area, but damaging winds and QLCS
tornadoes remain possible late tonight.
--In the worst case scenario, upstream pre-frontal confluence zone
initiates convection that remains at least quasi-discrete into our
area and interacts with a rapidly destabilizing PBL, resulting in a
more substantial tornado threat, followed by a QLCS wind/tornado
threat later.
Meteorological Analysis:
We won`t belabor the synoptic scale pattern/processes as we`ve
talked extensively about it the past few days. In short, a strong
mid-latitude system with the surface low this evening, falling to
990-mb or below by late evening. Anomalously strong and moist
southerly low-level flow is ongoing and will strengthen further. Our
environment will rapidly transform through the evening. This will
precondition the environment for deep/moist convection as forcing
for ascent increases with the approach of the trough.
Such rare/strong warm advection will result in a non-diurnal
temperature curve today, with our high temperature being at
midnight. The record for Indianapolis for 12/10 is 66, and may be
approached around midnight. Tomorrow`s record high is also 66 and
could be approached around and just after midnight.
Some important details with the trough geometry are that it is
positively tilted, and thus mean flow/deep shear vector orientation
is aligned oblique enough to the cold front for linear evolution.
For the linear convection along the front later in the night, we`ll
be watching particularly closely for rear inflow jets and surges
within the line as these reorientations are often where tornadoes
are favored. From the apex of the bows northward is where concern is
often highest for QLCS mesovortices and tornadoes. Also, it`s worth
noting that winds aloft will be particularly strong and momentum
transfer resulting in severe gusts will not be difficult to achieve,
even with weaker convection.
Preceding the QLCS threat, there is concern for open warm sector
convection driven by pre-frontal confluence area (similar to the
October 24th event in Missouri). These are usually linked to either
the old Pacific front that has become diffuse at the surface, and/or
the leading edge of stronger DCVA and its subtle surface reflection
that may not be particularly baroclinic, at least relative to the
aforementioned lagging primary front. Or, a subtle lead shortwave
trough. The warm sector is broad and a 2m theta-e surge in tandem
with steepening low-level lapse rates are seen in the models rapidly
overspreading the area early-mid evening. This is a classic
signature associated with many past nocturnal tornado events. Prior
to this occurring, convection should be relatively weak and
nontornadic, owing to a stable PBL north of the warm front.
Nevertheless convection could become fairly widespread where
isentropic ascent is maximized north of the warm front. However, a
dangerous parameter space will evolve once the warm sector spreads
into southern and central Indiana during the evening with
strengthening low level jet, causing surface-based buoyancy to
increase and support tornadoes. Further adding to the concern is
hints of an elevated mixed layer and associated steeper midlevel
lapse rates resulting in larger instability and stronger parcel
acceleration and more robust convection.
So, no argument that when coupled with strong deep layer and low-
level shear values, the parameter space is favorable for severe
storms and tornadoes this evening into the night. The concern then
goes back to pre-frontal storm mode and evolution. We attempt to
assess this potential below, but there remains uncertainty:
Water vapor channel imagery shows a lead shortwave trough over
northern Oklahoma with the main mid-upper trough now emerging from
the central Rockies onto the High Plains. Pinning down the exact
timing and magnitude of influence of this lead wave and/or
CFA/prefrontal convergence to delineate a more focused corridor of
concern is difficult. Hi-res guidance/HREF members reaffirm this
uncertainty with varying depictions but most do show at least some
pre-frontal development. More members than not are focusing this to
our southwest, and perhaps into southern Indiana, and this would be
along/near the favored 570-dm 500-mb height contour, which is old
school but it often works. This suggests that portions of northeast
Arkansas, southeast Missouri into southern Illinois, west Kentucky
and far southwest Indiana will have greater concern than our area.
Sometimes large convective blow-ups to our south can result in
dynamic PV adjustment and locally enhance subsidence limiting
convective potential. Even if this scenario were to happen, we
shouldn`t minimize the threat in our area as again we will at least
see some damaging wind and QLCS tornado potential with squall line
during the predawn hours.
Storm motions if prefrontal warm sector convection moves into our
area will be east-northeasterly at around 60 mph, and eastward
progression of the late night line of convection will be nearly as
fast.
Storms should be fairly progressive but could produce locally heavy
rainfall amounts in portions of southern Indiana that saw heavy
rainfall earlier in the week, with depressed flash flood guidance.
Flooding isn`t expected to be a primary concern, but heavy amounts
in areas that experience two or more storms could cause localized
flooding, particularly where the ground is saturated.
We will watch observational data closely through the late afternoon
and evening upstream and once we see the character and expansiveness
of upstream convection, we will be able to refine timing and speak
more confidently about severe magnitude. Mesoanalysis will be
critical later today and tonight.
To Our Partners/Messaging:
We`re asking our partners to help stress the danger of the overnight
severe potential. There are only a handful of days per year we ask
people to be particularly vigilant at night. Furthermore, December
is outside of our typical severe season and so overall awareness may
be low. Some ideas for items to stress today are to consider turning
on WEA alerts on phones if they`ve disabled them in the past, check
the status of warning devices such as weather radios and broadcast
media/private apps (multiple ways to get warnings are key), charge
devices ahead of time. Also, review sheltering plans, clean out
closets for sheltering, etc. Emphasizing that storms will be moving
fast (55-65 mph) and warning lead time could be a challenge,
especially for any QLCS tornadoes.
Thanks to our partners and your critically important roles, and
please never hesitate to contact us directly if you need anything
before, during, or after this severe weather event.
Saturday and Saturday Night....
Precipitation...
Around sunrise tomorrow morning, a strong cold front will pass
through central Indiana, providing chances of thunderstorms for
locations upstream (See Friday discussion for details on severe
threat). Current high resolution models are indicating the front
should be through central Indiana prior to noon EST. The near
surface layer behind this front is significantly drier, and should
limit any chances of wrap around moisture reaching the ground.
Temps...
Pre-frontal temperatures will be in the upper 50s to low 60s
tomorrow morning. Following the passage of the cold front,
temperatures will plummet 20+ degrees, resulting in afternoon
temperatures near 40. Dew point temperatures in the 20s and clear
skies should create an efficient environment for diurnal cooling,
allowing temperatures to fall quickly Saturday night. This will lead
to lows in the mid 20s; a shocking difference with temperatures 35-
40 degrees warmer just 24 hours prior.
Winds...
Near surface will increase significantly as well Saturday within the
drier, cooler airmass. The low will be nearing an efficient
cyclogenesis zone along a steep thickness gradient Saturday morning;
of which should allow for sharp surface pressure falls. This will
create a steep pressure gradient over the Great Lakes and Northern
Ohio Valley. This in combination with an expanding PBL in the
presence of increasing dew point depression in the late morning will
provide prime conditions for high winds and wind gusts. Sustained
winds should be between 20-30MPH for most of central Indiana
tomorrow morning. Sounding analysis shows momentum transfer from
around 2000 feet (just above the LCL), resulting in gust upwards of
50MPH in northern portions of central Indiana.
&&
.Long Term...(Sunday through Friday)
Issued at 246 PM EST Fri Dec 10 2021
A much quieter weather pattern will settle in for the latter part of
the weekend lasting through much of the upcoming week as surface and
upper level ridging dominate across the region.
Winds will back to southwest as early as during the day Sunday with
the center of the surface high passing through the Tennessee Valley.
This will enable a return to a warm advection regime with mild
temperatures quickly back in the Ohio Valley as early as Monday.
Highs in the 50s will be common Monday and Tuesday with low to mid
60s again possible on Wednesday ahead as southerly flow intensifies
ahead of another developing low pressure system over the central
Rockies.
The aforementioned low will intensify as it interacts with a
sharpening upper level trough and tracks northeast midweek. One
difference with this system versus the current one will be a track
further to the north and west with forcing aloft displaced to the
northwest of the region as well. The trailing cold front will bring
showers and perhaps some thunder Wednesday night into Thursday with
another cooldown to follow to end the week. But that being
said...the cooler temperatures will be just much closer to normal
for mid December than earlier in the week.
There are some hints of the cold front getting hung up just south of
the area next weekend which may lead to more unsettled weather and
possibly a surge of colder air that may enable some snowflakes to
mix in with rain. Ultimately...winter showing no signs of appearing
across the region within the next 7 days.
&&
.Aviation...(00Z TAF Issuance)
Issued at 628 PM EST Fri Dec 10 2021
IMPACTS:
* IFR or worse ceilings will continue this evening into the
overnight, with fluctuations in both ceiling and visibility
likely, particularly with thunderstorm activity.
* Convection will develop later this evening and impact all
terminals through the predawn hours
* Southerly wind gusts will increase to near 30kts by late
evening...higher winds possible in and near thunderstorms
* Low level wind shear this evening into the overnight.
* winds will veer to westerly with the cold frontal passage early
Saturday: gusts at 30-40kts expected throughout much of the day
Saturday
Discussion:
Poor flying conditions will be the rule this TAF period as rapidly
strengthening low pressure pushes northeastward into the Great
Lakes and drags a strong cold front through the area.
Widespread restricted ceilings, primarily IFR or worse, are expected
in the warm sector overnight, although there will likely be
fluctuations in both ceiling and visibility, particularly in
thunderstorm activity.
Expect convection to continue to develop to our west and southwest
this evening and begin to impact the terminals after about 03Z or
so, and have used TEMPO groups to try to better define impact
windows, although uncertainty remains in the high shear, relatively
low instability environment.
Surface winds are likely to become gusty in short order, although
will still carry low level wind shear given extremely strong
southerly/southwesterly flow just off the surface overnight.
After the front passes late tonight into early Saturday morning,
there may be a brief period where ceilings improve before widespread
MVFR stratus redevelops.
Winds will become quite strong on Saturday with gusts at times well
into the 30KT to near 40KT range, strongest to the north. These
gusts will dissipate very late in the period in typical diurnal
fashion.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 7 AM to 5 PM EST Saturday for INZ021-028>031-
035>042.
&&
$$
Update...Nield
Short Term...BRB/Updike
Long Term...Ryan
Aviation...Nield
Area Forecast Discussion
National Weather Service North Platte NE
922 PM CST Fri Dec 10 2021
.UPDATE...
Issued at 922 PM CST Fri Dec 10 2021
Current radar trends and surface observations have indicated that
the threat for accumulating snow has ended across western and
north central Nebraska. Winds have diminished to 10 to 15 MPH with
gusts up to 20 MPH noted at O`Neill and Broken Bow over the past
hour. With the threat for accumulating snow ending and diminishing
winds, will be canceling winter headlines for the area at 9 PM
CT. Temperatures will be cold tonight, particularly in the west,
where some limited clearing has occurred over the past hour.
UPDATE Issued at 603 PM CST Fri Dec 10 2021
Recent satellite imagery indicates some drier air trying to work
into southwestern Nebraska and the southeastern Nebraska panhandle
over the past 1 to 2 hours. This has ended the snow threat across
our panhandle counties and far SW Nebraska. However, radar returns
over the past hour have increased over the sandhills into northern
Nebraska. With the increasing radar returns and some support from
the HRRR and NAMNEST reflectivity products, decided to extend a
winter weather advisory across portions of the eastern Sandhills
and north central Nebraska through 10 PM CT. The winter storm
warning for Holt and Boyd counties as well as the winter weather
advisory for Garfield and Wheeler counties will continue through
midnight CT. Updated headlines and forecast has been sent out.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 410 PM CST Fri Dec 10 2021
The main forecast challenges heading into the weekend relate to the
latter part of the winter storm and yet another big warmup. Winter
weather headlines remain in effect for northern Nebraska as
accumulating snow continues and extended the Advisory for Garfield
and Wheeler through 06z. The western half of the headline area
should be good to let expire at the planned 00z. In the wake of the
storm, a broad upper ridge builds back into the Central US, allowing
temperatures to rise well above normal (at least for those without
significant snowpack).
This evening and tonight... The surface low currently (as of 21z)
over eastern KS zooms northeastward, reaching western MI by sunrise.
The upper trough moves nearly as quickly with its axis passing
through all of Nebraska by midnight and the ridge taking over by
morning. The second main deformation band is underway, stretching
from near KGLD to past KFSD. Extended PoP across central Neb to
account for this activity. Could still experience some bursts of
heavier snow, especially invof KONL where forecast soundings
indicate decent lift and saturation within the DGZ. There`s also a
window of 2-3 hours of an isothermal layer in the DGZ to really help
bump of SLR`s and quick accumulation. Potential still exists for an
additional 4-6" in Boyd and Holt Counties and 1-3" in surrounding
areas. Farther west, expect continued waning of snowfall as
isentropic downglide takes over and mid-level dry air filters in.
However, there may be enough remnant forcing, especially near the
Pine Ridge, for wrap-around snow showers. Some higher res solutions
suggest this potential through 03z until the trough finally kicks
out. Northerly winds will also be gusty due to rapid surface
pressure changes with the departing low, strong H7-85 flow, and a
nearby PV anomaly. Gusts will taper somewhat after sunset, but may
remain high enough overnight to inhibit full boundary layer
decoupling. Made some adjustments to the min temp forecast to
reflect the recent deep snowpack, most notably extending the much
colder lows around the Pine Ridge farther east. Forecast values in
the single digits are a good 5-10F below guidance, which seem
reasonable given eventual clearing of clouds. Reports from observers
near KGRN and KVTN indicate 8-12" of fresh snow. In the southwest
and mainly the river valley, dropped temps slightly in case winds
relax enough. For central Neb, raised lows slightly due to later
snowfall and slower clearing of clouds. Lows range from around 2F at
KGRN to around 10F in the Platte Valley to mid teens north central.
Saturday and Sat night... The upper ridge gains more influence over
the High Plains, placing Nebraska into northwest flow. Meanwhile, a
large surface high pressure system takes over with one centroid over
the western Rockies and another in the southern Plains. These
factors along with notable WAA at H85 will provide fair conditions
and moderating temperatures, at least across southwest Nebraska
where snowpack is minimal. Bumped up max temps along/south of I-80
into the lower/mid 40s, which is at the top end of NBM envelope but
middle of MOS guidance. To the north, kept highs in the 30s where it
will take some time to melt off 6"+ of snow. Wind will be rather
gusty in the afternoon as the H3 upper jet passes by and drives some
stronger flow into the mid levels. Downsloping west winds at H85 at
30kts will mostly mix to the surface, resulting in gusts of 25+ mph.
The somewhat mild temps in the far southwest will actually drive
humidity values down below 20%, and when combined with gusty winds,
there is an elevated fire weather risk. Overnight lows will be
another dance between warm air advection and southwest winds in the
low levels, remnant snowpack, and mostly clear sky. For now, used a
general blend with upper teens to lower 20s.
.LONG TERM...(Sunday through Friday)
Issued at 410 PM CST Fri Dec 10 2021
Next week, the main upper ridge spreads into the Eastern US and
amplifies while a trough digs into the Desert Southwest. Some long
range solutions close off a low and swings it right through the
central Plains mid next week, accompanied by a rapidly deepening lee
side surface low. This setup is big forecast concern as it will
likely bring strong winds to western Nebraska and another chance of
precipitation, some of it wintry. Some guidance hints at 50kt+ gusts
on Wednesday, which would necessitate High Wind products and will
definitely need to be monitored. The other big story is the warmup
that comes with the ridge. Strong southerly flow and continued WAA
will drive H85 temps to near 15C, which may translate to highs well
into the 50s and even lower 60s. Fire weather concerns will also be
heightened in the southwest where antecedent conditions are mainly
dry and humidity values will be lower.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 525 PM CST Fri Dec 10 2021
Recent radar trends show enhancement with light snow filling in
across central Nebraska. Expect this will keep conditions MVFR
tempo IFR at both KLBF and KVTN for the first few hours of the
valid period. May even see a brief period of LIFR vsbys at KVTN
through 02Z. However, conditions will be improving rapidly this
evening with snow moving off to the east and cigs rising to VFR
before Midnight. VFR will then prevail through the end of the
valid period.
Winds will be gusty mainly at KLBF this evening. As skies clear
and the surface cools quickly expect winds will decouple early
tonight and bring an end to gusty conditions through the overnight
period. Will see some gusts return Saturday afternoon but
generally under 25kt.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Buttler
SHORT TERM...Snively
LONG TERM...Snively
AVIATION...MBS
Area Forecast Discussion
National Weather Service Louisville KY
750 PM EST Fri Dec 10 2021
.Forecast Update...
Issued at 750 PM EST Fri Dec 10 2021
Tornado Watch #554 has been issued for the western two-thirds of our
CWA until 3 AM EST. Scattered pre-frontal convection has already
developed across the lower Ohio/Mississippi River confluence and
will quickly race northeastward into our western CWA within the next
hour. The VAD wind profiler data from VWX/HOP radars have shown
increasing low level wind shear resulting in very strong helicity in
the lowest 1 km (resulting in >400 m2/s2). Model soundings along our
far western CWA do show a bit of an inversion and farther east
toward the I-65 corridor we are seeing that inversion show up on
AMDAR soundings. RAP soundings over the next few hours show dew
points slowly increasing west of I-65, which may be enough to allow
those storms to become surface based when they move into the CWA.
Do want to convey that we expect another Watch will be needed
farther east in our CWA for the pre-dawn and around sunrise time
frame, but that will likely come at a later time tonight.
&&
.Short Term...(This evening through Saturday)
Issued at 344 PM EST Fri Dec 10 2021
...SIGNIFICANT EPISODE OF SEVERE WEATHER EXPECTED TONIGHT AND EARLY
SATURDAY MORNING...
====================================
Synoptic Discussion
====================================
Deepening mid-level trough axis over the Plains will translate
eastward this evening and overnight. The trough axis is forecast to
remain positive to neutrally tilted as it moves toward our region.
Initial mid-level vorticity lobe moving NE across KS/OK this
afternoon will lead to initial convective development across
MO/AR/WKY/WIN/SCIL as early as late this afternoon/evening. Deep
tropospheric wind fields are expected to overspread the Ohio Valley
along with a strengthening low-level flow that will transport
deep/rich Gulf moisture northward into the region. The net result
of this combination of increasing instability and shear will lead to
a severe weather episode over the Ohio Valley tonight and early
Saturday morning. Damaging winds in excess 60 MPH and isolated to
scattered reports of tornadoes are expected. In addition, copious
amounts of moisture will lead to heavy rainfall which may result in
some minor flooding issues across the area.
====================================
Meteorological Technical Discussion
====================================
Surface warm front is rather diffuse this afternoon, but boundary
looks to be crossing through the region at this time, based on band
of elevated convection oriented from W/C IN southeast through
eastern KY. This activity will continue to move to the northeast
this afternoon. Once this activity clears out, we will be in the
open warm sector with moisture advection continuing through the
evening hours. Dewpoints are currently in the mid 50s across the
region but are approaching 60 in our southwest areas. A stronger
dewpoint surge is currently in progress out along the MS river and
dewpoints have already risen into the upper 60s over far southwest
Kentucky.
In the near term, a mid-level short wave evident in the GOES
moisture channel was moving NE across OK/KS. This feature will
translate northeastward into the Midwest this evening. This feature
will likely lead to initial convection firing over AR/MO/WKY/WTN and
SCIL later this afternoon/evening. Further east over our area,
continued moistening and theta-e advection will continue across our
region. The front edge of a strong low-level jet axis will work
northeastward into very lower part of the Ohio Valley. As this
occurs, additional cooling aloft is expected to overspread portions
of SWIN/WKY which should allow higher instability to develop as mid-
level lapse rates steepen. These two items will also help erode the
elevated mixed layer of warm air aloft and result in a possible
uptick in surface based convection across our western CWA this
evening. Given the parameter space, initial cells that develop will
like be discrete/scattered and given the shear profiles a mix of
multicell and supercells are expected. These storms will likely
race off to the northeast at 55-60 MPH. Threats with this activity
will be damaging winds, perhaps some marginally severe hail, and
isolated tornadoes.
Many members of the various short range ensemble models generally
support this idea, i.e., more members that not. However, the
eastward extent of pre-frontal convective development this evening
remains uncertain due to unknowns involving how much of the EML will
erode and whether surface based convective inhibition will remain.
In general, the best chances of convective development this evening
will be in areas along and west of the I-65 corridor.
Later in the overnight, it appears that additional convection will
develop given the instability and deep forcing resulting in more of
a linear QLCS. Given the strong shear and substantial front-
parallel components of the deep layer flow, downward momentum
transfer should yield instances of wind damage within the convective
line. Additionally QLCS mesovortices within the squall line where
bows and surges develop may produce several instances of embedded
tornadoes. This line will work through region during the late night
hours and continue into our eastern sections after sunrise Saturday.
The expected progressive nature of this line should result in
generally short residence time of heavy rainfall over any one
particular area. Additional QPF information may be found below in
the Hydrology section of the discussion.
We will continue to monitor observational data closely this
afternoon and evening especially upstream. As cells develop and the
convective evolution becomes more certain, we will be able to update
our timing and speak a bit more confidently with regards to the
possible magnitude of this severe weather event.
====================================
Important Messaging
====================================
As we have mentioned over the past 24 hours, we want to stress the
danger in the overnight severe weather potential. Historically,
tornadic and widespread severe weather events in the month of
December are rare, although we`ve had a couple of events in the last
10 years (12/2013 and 12/2015). We would like to emphasize the
following topics:
1. Have multiple ways to get warnings overnight. Leave your cell
phone on and have WEA alerts turned on. Check the status of your
weather radio and make sure it is functioning. Charge/replace
batteries in your alert devices.
2. Review your severe weather plans for your household. Review
where your lowest level interior rooms in your home are and have
space ready in there to shelter. Put as many walls as you can
between you and the outside of your home. If you have a basement,
make sure a shelter space in an interior room or under substantial
framing is available and ready in the event of a warning. Stay away
from exterior windows and doors.
3. If you live in a mobile home, consider finding a more substantial
shelter this evening with friends and/or family. Even in non-
tornadic winds, gusts of 60+ MPH can easily flip mobile homes
whether they are tied or bolted down.
4. These storms will be moving quickly with speeds of 55 to 60 MPH.
Warning lead time on these storms could be a challenge especially
involving mesoscale vortices within the anticipated squall line.
====================================
Forecast Confidence
====================================
Tornado Threat:
West of I-65: Medium-High
East of I-65: Low-Medium
Wind Threat:
High confidence across our region
Flooding Threat:
Medium confidence across our region
.Long Term...(Saturday night through Friday)
Issued at 320 PM EST Fri Dec 10 2021
After an stormy start of the weekend, the latter part of the
forecast will certainly be more relaxed. Ejecting upper wave will
give way to anomalous ridging aloft and surface high pressure for
the easternmost two-thirds of the CONUS. Meanwhile, upstream flow
will feature a series of digging troughs which will slowly advance
towards the central US by midweek, eroding the high-pressure dome.
Sunday-Monday... Morning temperatures both days will be below
freezing thanks to a combination of CAA and radiational cooling.
Afternoon highs will gently move from the upper 40s on Sunday to the
lower 50s at the start of the work week. A dry air mass in place
secures clear skies and plenty of sunshine as the surface high
pressure moves to the Mid Atlantic states and an West Coast trough
moves to Central Plains.
Tuesday-Wednesday...The aforementioned large scale configuration
imposes a southerly wind and accompanying increased theta-e
advection. As a result, temperature readings will progressively
climb and the forecast reflects maximum temps around the upper 60s
south of the Parkways by midweek. Expect winds to start picking up
on Wed with gusts in the 10-15 mph range while cloud coverage spread
our area.
Thursday-Friday...As the Central Plains trough progresses to the
Midwest/Great Lakes region, it pushes an attendant cold front to the
Ohio Valley. However, strong ridge aloft anchored over the SE CONUS
will inhibit further southward momentum of the baroclinic zone,
therefore, it could stall south of our area or right above us. There
is still some timing uncertainty with this evolution as noted in the
WPC mid-level EOF cluster patterns. That being said, there is
increasing agreement for warmer temps on Thursday which could result
in record high low for SDF. The latest NAEFS ESA guidance has 850-mb
temps around the 90th climo percentile. Winds gusts will be blowing
from the southwest around 15-20 mph on Thursday as the front sweeps
by central KY and diminishing by Friday. Finally, precipitation is
boosted for the end of next week and probably next weekend with the
frontal passage and subsequent stalling nearby. This scenario is
also reflected by the slight risk of heavy precipitation delineated
by CPC during the Dec 17-20 timeframe as return flow from the GoM
leads to high rain chances.
&&
.Aviation...(00Z TAF Issuance)
Issued at 649 PM EST Fri Dec 10 2021
IMPACTS:
- Low stratus early this evening with scattered showers
- Southerly winds increase become gusty tonight
- Gusts tonight and overnight of 30-35kt
- Strong to severe thunderstorms moving through overnight
- Strong/gusty southwest to west winds will be seen on Saturday
behind a cold front
DISCUSSION:
A strong storm system will approach and pass the region during this
TAF cycle, strong & impactful storms, gusty gradient winds, low
ceilings at times. In addition, the most intense thunderstorms will
briefly reduce visibilities below 2 SM.
For the evening and overnight period, we expect scattered convection
to develop over the next 1 to 2 hours across western KY and
southwest Indiana. After scattered storms (some supercells), these
storms are expected to organize into a well developed squall line
that will race across the region. While not explicitly defined in
the TAFs, localized gusts over 50kts can be expected in this line in
some areas. Additionally wind fields aloft are very strong and LLWS
is expected at all the terminals this evening and into the overnight
period.
Convection should clear the terminals around or just after sunrise
Saturday however, scattered rain showers and gusty southwest to
westerly winds are expected throughout the day.
CONFIDENCE:
Medium-high on all elements.
&&
.Hydrology...
Issued at 320 PM EDT Fri Dec 10 2021
Deep, moist SW flow characterized by PW~1.5" is being advected along
the warm sector ahead of an amplifying upper-level trough. Attendant
cold front will swing through our area Friday night/Saturday morning
bringing a strong-to-severe line of thunderstorms. Heavy rain from
this event might provoke localized flooding and river flow rises,
especially streams that experienced flow peaks during the last event.
Current forecast package is considering QPF in the 1-1.5" range
associated with the main frontal passage. Meanwhile 3-hr FFG sits
between 2-3" area-wide and the 0-40 cm soil moisture is still
average per the latest NASA SPORT analysis. Therefore, rainfall
should be largely managable giving minimal runoff. Additionally,
HREF 1-hr probabilities for QPF greater than 1" is less than 20%,
which aligns well with the progressive nature of the system. Only
problem for stagnant water is in poor drainage areas and low-lying
locations. WPC still manintains a Marginal Risk (1 out of 4) of
excessive rainfall due to the strong linear forcing, theta-e
advection, and any localized areas of training convection given the
alignment and strenght of the LLJ and the cloud-layer mean wind.
Another factor to consider is the antecedent hydrological conditions
of rivers that experienced flooding/rises this past Monday and
respond quicly to short periods of heavy precipitation, such as:
Rochester Ferry, Paris, Peaks Mill,and Boston. Other rivers worth
monitoring during the next 24 hours per the lastest AHPS/HEFS
forecast are the Green and White Rivers. It is important to mention
that the OHRFC does not expect any widespread risk of significant
river flooding.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...BJS/DM
Short Term...MJ
Long Term....ALL
Aviation...BJS
Hydrology...ALL
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
953 PM CST Fri Dec 10 2021
.MESOSCALE DISCUSSION...
Issued at 952 PM CST Fri Dec 10 2021
Warm front has surged north and lies roughly from Chicago west-
southwest to southern DeKalb/northern LaSalle County. Modifying
recent ACARS soundings from MDW for observed T/Tds in the warm
sector over our CWA suggests there is a weak near surface
inversion present with very weak instability. Despite the minimal
instability and weak inversion near the surface, the strongly
forced convection is taking full advantage of the extreme low and
strong deep layer shear. Have seen transient circulations
developing within the small short line segments. Have also seen
some near severe/isolated severe gusts with these short line
segments, which isn`t surprising given 50kt winds about 1500ft agl
on the KLOT VWP.
Over the next 1-2 hours, storms should continue moving eastward
into northwest IN and into a very similar environment that they
are in now. Given this, not anticipating much if any weakening.
Primary threat should continue to be locally damaging wind gusts.
While there is a weak near surface inversion, the extreme shear
and strong dynamics suggests that the subtle inversion could be
overcome with more intense convection. Will need to closely watch
for any transient circulations or developing mesovortices for
tornado potential over the next hour or two.
- Izzi
Issued at 655 PM CST Fri Dec 10 2021
No significant updates early this evening as we continue to
monitor upstream convective trends as well the evolution of low-
level thermodynamics ahead of and along a warm front over central
Illinois. At this point, the rapidly develop convection west and
northwest of St. Louis is of most interest as the associated
airmass quickly advects NE into central Illinois over the next few
hours. The potential for surface-based convection into the CWA
remains unclear even at this hour.
Near-term CAMs still show variability in overall convective
evolution, but the fairly consistent trends in the HRRR along with
reasonable depiction of how convection has developed thus far
supports leaning more toward its guidance for this evening. Our
greatest severe threat will likely be tied to any upscale
growth/congealing of the recent convection in northeast Missouri.
Any mature convective line will have the capability of punching
stronger winds through any existing shallow inversion, and may
even have enough micro/mesoscale dynamic influence on the
environment to weaken existing near-surface stability immediately
ahead of the line. Additionally, recent convective growth with
some surface-based potential in southeast Iowa indicates low-level
stability can quickly be overcome within this dynamic
environment.
Even more, gravity wave packets within the significant shear
across the frontal inversion have been evident on radar this
evening. these features can be of concern for convective
initiation or potentially helping to bring down stronger winds
with any slightly elevated convection. With all that said,
concerns for severe convective winds into the CWA, primarily south
of I-88, remains warranted through at least midnight, with the
greatest focus in the 9pm-midnight period. The potential for local
thermodynamic modification by any mature convection bears close
monitoring for low- level rotation under any enhanced updrafts,
especially south of the Illinois/Kankakee River Valleys.
Kluber
&&
.SHORT TERM...
Issued at 320 PM CST Fri Dec 10 2021
Through Saturday...
Multi-faceted hazards into Saturday with the strong storm system
impacting the region, including:
* Dense fog threat into early evening
* Thunderstorms and associated severe threats later this evening
into the early overnight
* Strong winds from the southwest to west pre-dawn Saturday
through the early afternoon
* A period of wind blown mainly light snow Saturday morning for
portions of northern Illinois
Regarding the going Wind Advisory, main change was to expand the
Advisory to include Winnebago, Boone, Lee, and Ogle Counties, in
effect from 3 AM to 12 PM.
[Dense Fog]
After the visibility improvement in the late morning, starting to
see visibility creeping back downward for locales south of I-80
and also deteriorating visibility on webcams in downtown Chicago.
As the warm front sharpens into the early evening, we may well
need to issue a new Dense Fog Advisory that could also include
counties farther north. May need to start with some initial
counties in an advisory in the near term (within next hour or two)
if trends continue and then assess from there.
[Thunderstorms and Severe Threat]
Lead warm advection wing showers spreading east-northeast as of
this writing have had isolated embedded thunder, so have included
slight chance/isolated wording over the next few hours with this
activity.
Shifting to the severe weather threat tonight, SPC outlook
20z update maintained the level 3 (Enhanced) risk into areas
south of US-24, with no changes on northward extent of level 2
(Slight) and level 1 (Marginal) risk areas that were expanded
northward earlier this morning. As can best be gleaned from
guidance trends and plausible scenarios, there is solid agreement
in robust deep moist convection initiating in the early to mid
evening (00z-02z) near the MS River and then quickly tracking
east-northeastward. Then toward through a few hours after midnight
immediately ahead of the sharp system cold front, there is
another window of thunderstorms.
See below for more details, but in summary, the evening round
could be mainly elevated but have a wind threat. Window for
surface based severe threat would be tied to the 2nd potential
round, with this also having a damaging wind threat and possibly a
brief tornado threat. All in all, the presence of sufficient
MUCAPE tonight for a high shear low CAPE setup amidst very strong
dynamics and kinematics supports the level 1-3 risks from SPC. And
speaking of the shear and low level SRH, it is extreme as you`d
expect for a wintertime setup.
We`re still not in the realm of mesoanalysis for the local area
yet being well north of the warm front, but there continue to be
some key elements to watch as the warm front advances northward.
An exceptionally juicy (upper 60s-lower 70s Td) air mass resides
in the open warm sector in AR, far southern MO, and TN. The 60F
isodrosotherm has pushed to or just north of the latitude of St.
Louis as of this writing. Guidance varies on how far north the
60F+ dew points get this evening, and HREF CAMs currently have a
decent handle, so it`s too soon to say which guidance is on the
right track, though we did lean toward the slightly more
aggressive HRRR.
Also have questions on how much if any role the existing fog/very
low stratus bank has on evolution of the air mass and available
instability this evening. Would think that initially prior to
stronger pressure falls, the fog would somewhat inhibit northward
advance but then quickly strengthening southerly flow aloft should
advance it northward. If anything, the existence of this very low
cloud cover and obvious low level inversion may shorten the time
window in which severe weather is possible this evening/tonight.
A consistent item seen in poring through model forecast soundings
south of the warm front this evening is a pretty distinct low
level inversion around 900 or 925 mb. This seems to be tied to the
extreme warmth at 925 mb (+17C at LZK/Little Rock and +16C at
SGF/Springfield MO) set to advect over our area. Most recent
SPC/RAP Mesoanalysis shows +15C isotherm at 925 mb reaching KSTL.
Even with the unseasonably warm and moist air mass in the warm
sector, this magnitude of warmth at 925 mb is not being overcome
by surface warming through the bulk of the evening. This leaves
low-level inversion in place and providing rather large SBCIN
except for maybe a very short 1-2 hour window where that capping
can be overcome. As mentioned earlier, the likely evening round,
depicted as a QLCS type or mixed with semi-discrete supercells on
some recent HRRR runs, quite possibly could remain mostly
elevated. Temperature trends will need to be closely monitored, as
observations being just a few degrees warmer would lessen the
inversion.
The above being said, think the modeled low level inversion does
present uncertainty as to the magnitude and mode of the severe
threat within the CWA. At this time, think the primary threat will
be damaging winds in QLCS storm mode during the evening, as the
tremendous momentum aloft could be mixed down through the
inversion (perhaps not in a widespread manner). Suspect that any
tornado threat would be mainly of the QLCS variety, though it`s
tough to say how that antecedent low level inversion would play
into the tornado threat. In low topped supercell storm mode,
decent likelihood of discrete/ semi-discrete cells remaining
elevated may limit severe threat aside from rear-flank downdraft
punch and perhaps marginally severe hail.
Then overnight (~05z-08z), immediately ahead of and along the
front, strong low level advection could help the environment
recover for a short 1-2 hour window of a surface based severe
threat, per consensus on forecast soundings. SPC outlook is a
reasonable approximation of the relative threat during this time
as well, with points south more favored. Confidence is a bit
lower by this time, as we`ll need to see how much the air mass
gets worked over, and if the threat truly becomes surface based.
We may also start to see some drying and rising LCL heights at
this time, suggesting that perhaps damaging wind threat will be
primary again. The tornado threat, while certainly not one to
completely discount given the extreme low level shear profile, is
low confidence.
Needless to say, and to reiterate, observational trends will need
to be closely monitored this evening, as to how well the models
are handling the temperature profile and dew point surge. In
addition, ILX will be launching a special RAOB sounding at 02z or
03z, which hopefully will help get a better handle on the
environment that will be in place in the mid-late evening. For the
00z sounding, they will still be north of the warm front. Finally,
the cold front sweeping across the area toward and beyond 09z will
end the convective threat and shift our attention to the strong
southwest to west winds.
Castro
[Wind and Wind-blown Light Snow Threat Saturday]
Intense pressure rises on the order of 12+ mb/6 hrs coupled with
strong cold air advection and a 50 to 60 kt low level jet aloft
will generate strong winds late tonight through early Saturday
afternoon. This will be as the surface low deepens into the low-
mid 980s mb over central Lake Michigan by 12z Saturday. Forecast
soundings indicate that winds of 45 to 50 mph are expected to be
mixed down to the surface across the CWA, with a potential for
gusts to exceed 50 mph right on the leading edge of the rapid
onset of CAA with pressure rise/fall couplet, as well as in the
deeper mixing during Saturday morning.
The strongest gusts and best chance for ~50-55 mph gusts (and
non-zero threat for 60 mph gusts) are most likely across the
southeastern half or so of the CWA, but recent forecast guidance
does support gusts around 40 to 50 mph occurring in Winnebago,
Boone, Ogle, and Lee counties late tonight through Saturday
morning. Because of this signal, the wind advisory starting at 3
AM CST on Saturday has been expanded to include Winnebago, Boone,
Ogle, and Lee counties until noon on Saturday. The rest of the
area will remain under a wind advisory until 3 PM CST Saturday
afternoon. The winds will slowly begin to ease late Saturday
afternoon and throughout the evening with gusts around 15 mph
expected Saturday night.
The strong short-wave trough axis will be pivoting overhead
Saturday morning, so during this time, still looks like a flip to
mainly light snow is plausible near and north of I-80 and especially
for northern tier where highest PoPs are. Model soundings vary on
how deep saturation gets, with some models pretty dry in DGZ and
some sufficiently saturated up to -12 to -13C. This suggests that
the snowflakes will be poor quality/small. Temperatures will crash
to the lower-mid 30s behind the cold front, with profile quickly
becoming snow supportive, so the main question is the aforementioned
saturation depth. Given such mild temperatures late tonight ahead
of the cold front, think that road accumulations are pretty
unlikely and main impact would be reduced visibility. Can`t rule
out some slick spots on elevated surfaces, with accumulation
primarily a coating to a few tenths on grassy surfaces. The
precipitation will end by mid day, with clouds quickly eroding
west to east yielding sunny breaks before sunset.
Castro/Yack
&&
.LONG TERM...
Issued at 123 PM CST Fri Dec 10 2021
Saturday night through Thursday...
Forecast thinking has not changed during the period. Please
reference the previous discussion below for details.
The main forecast point of note in the long term is the
pronounced warmth next week, with all days looking to be above
normal and a period midweek with 20 to 25 degrees above normal,
including possibly a record high on Wednesday and warmest December
day in several years (at least since 2017).
As has been the case for several weeks, the upper air pattern this
coming week remains notably progressive across the country, even
with strong synoptic lows and highs. For the latter half of this
weekend, a 1030 mb high south of the area will be scooting
quickly to the east. This will keep the CWA under the pressure
gradient on its north promoting breezy southwest winds on Sunday.
Both Sunday and Monday should be sunny as well, and support highs
near 50. Monday may even overperform given 850-925 mb temperature
climatology for this time of year and the dry air mass. Have
leaned toward warmer guidance as has been the forecast trend for
this period. Neither of the days stand out as a fire weather
concern based on the stronger gusts on Sunday and lower relative
humidity values being on Monday.
On Tuesday into Wednesday, an upper level ridge will build
northward through the Great Lakes, with highly anomalous heights
values at 500 mb. Deep low pressure in the lee of the Rockies
will strengthen over the northern High Plains area. A warm front
will approach and then lift north of the area, replacing the dry-
ish air mass that starts the work week with a very moist one for
this time of year on Wednesday. Tuesday should see increasing mid
and high clouds at least as warm front lifts north, so temps may
be similar if not a degree or two warmer than Monday in spots.
Increasing pressure falls Tuesday night will result in increasing
southerly winds and rising temps, providing a springboard for
Wednesday`s near record or record warmth. It will be windy with
southerly gusts up to 30-35 mph, with strong surface advection of
the warmth and moisture. At least low-mid 50s Td appears likely
and any higher would increase upside potential for high temps.
Conceptually, this pattern still continues to favor low stratus
due to strong south-southwesterly flow. With isentropic ascent
from strong WAA, could even see some sprinkles or drizzle break
out.
The 850 mb temps of at least 10-15C are still shown for Wednesday
and this again is near top of the charts for December, so with all
the above factors in play, comfortable with the 61-66F range from
the NBM. Daily record high on Wednesday (12/15) for Rockford is
58F and is 64F for Chicago, both set in 1971. Strong south-
southwesterly winds look to result in a positively spring-like
Wednesday night likely not dipping below 50F ahead of the cold
front. Uncertain timing of the cold frontal passage will dictate
how warm temps get until the frontal passage, with mid-upper 50s
in current forecast. Should be a band of strongly force showers,
possibly even with a few storms with the front, so chance PoPs in
gridded forecast appear reasonable, though would be shorter-lived
than in the current blend-provided, broad-brushed grids.
MTF/Castro
&&
.AVIATION...
For the 00Z TAFs...
Concerns for the near term include low cigs and vsbys in the rain
shield ahead of an approaching center of low pressure. Current
values are not quite as low across the area as expected earlier,
so elected to bump the initial vsbys up to MVFR in the 3 to 5 mile
range. Thunderstorm chances are not great early this evening, but
do ramp up somewhat as midnight approaches, more for the Chicago
terminals than RFD, and with MDW and GYY probably favored a bit
more than ORD and DPA.
Winds veer from easterly early this evening to southerly by later
this evening, around to southwesterly by midnight, then to the
west during the morning. The flip from south to southwest toward
midnight will be accompanied by a significant increase in speeds
and gusts as a cold front pushes through. These magnitudes are
expected to persist through late morning and very gradually
subside during the afternoon. Before the surface winds increase
this evening, and before they really ramp up behind the front in
the early overnight hours, winds riding over the stable surface
layer will be quite strong, so we have maintained a mention of
LLWS.
The last item to mention is the chance of some light snow toward
mid-morning as an upper level wave of energy behind the low swings
across the area. At this time this is not expected to produce much
more than flurries, but there could be a brief period of vsby
reductions.
Lenning
&&
.MARINE...
Issued at 123 PM CST Thu Dec 9 2021
...Higher end westerly gales Saturday morning...
A strong and deepening low pressure system will track northeast
over the southern half of the lake very late tonight through
Saturday morning. Ahead of this system, southerly winds will be
blowing near or into Small Craft Advisory this evening into early
overnight before the cold front arrives. Also in the hours ahead
of the cold front, convection is likely, and some of this will
potentially be strong and mix down winds in excess of 35 kt.
After the cold front passes around 3-4 A.M., solid westerly gales
of 40-45 kt will occur with continued high confidence. A few
storm force gusts may even materialize during Saturday morning.
Winds will slowly ease during the afternoon into evening on
Saturday.
No major changes have been made to the going forecast, and thus
the Gale warning remains in effect from 3am through 3pm Saturday.
MTF/KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory...ILZ005-ILZ006-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-
ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-
ILZ106-ILZ107-ILZ108...3 AM Saturday to 3 PM Saturday.
Wind Advisory...ILZ003-ILZ004-ILZ008-ILZ010...3 AM Saturday to
noon Saturday.
IN...Wind Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...3 AM
Saturday to 3 PM Saturday.
LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...3 AM
Saturday to 6 PM Saturday.
Small Craft Advisory...nearshore waters until 3 AM Saturday.
&&
$$
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Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
640 PM CST Fri Dec 10 2021
.UPDATE...
Issued at 640 PM CST Fri Dec 10 2021
A narrow band of intense snow stretches from New Ulm, to the southern
Twin Cities metro, eastward to New Richmond and approaching
Ladysmith. It is within this band rates are now 1 to 2 inches per
hour. The band is nearly stationary and is pivoting as the system
advances to the east. Increased QPF within this corridor to highlight
the mesoscale heavy snow band. Amounts have already reached 6 inches
in places in the south metro and it`s highly likely now that some
will exceed a foot by late tonight. Farther to the south, while
radar may be some beam overshooting some of the more intense echos,
visibilities also indicate the snow isn`t as intense there. Didn`t
change too much in those locations yet, but it`s expected the
heaviest totals will be along the aforementioned axis farther north.
&&
.DISCUSSION...(This evening through Thursday)
Issued at 141 PM CST Fri Dec 10 2021
Key Messages: Winter storm remains on track to cause significant
travel impacts across parts of Minnesota and Wisconsin.
1) Periods of 1 inch per hour snowfall rates likely late this
afternoon and evening under the heaviest band.
2) Totals of 8-12" likely within that band of snow by the time the
snow ends late tonight into Saturday morning.
3) Northerly winds of 20 to 30 mph will lead to some blowing and
drifting snow.
TODAY AND TONIGHT`S WINTER STORM - No significant changes from the
previous forecast. The Upper Level wave driving this system was
located over Nebraska. An area of isentropic ascent and
frontogenesis developed along the thermal gradient ahead of this
wave. Snowfall amounts under this band will be in the 8 to 12 inch
range, with locally higher amounts near 14 inches possible. HREF
guidance shows high probabilities of snowfall rates of at least an
inch per hour, with some signal for 2 inches per hour. The intensity
of the snowfall is probably going to be the most impactful part of
this storm. Some thundersnow is possible as the system develop later
this evening. The snow should quickly dissipate from west to east
overnight.
Another aspect of the storm is the northerly winds. The surface low
drops from 994 to 987 mb as it tracks from Kansas up towards
southern Wisconsin. This strengthening system will support stronger
surface winds, but the cold air advection never moves across
southern the region. As a result, winds will be breezy, with
easterly gusts near 25 mph, and northwesterly gusts near 30 mph, but
they should top out around there. That means areas of blowing and
drifting snow, but not expecting blizzard condition. The reduced
visibility will be more so a result of the aforementioned snowfall
rates, and less a result of blowing snow.
In summary, HiRes guidance from the early afternoon runs of the HRRR
did reduce the QPF across the Twin Cities metro, but there is enough
other guidance such as the HopWrf and HREF that maintains a band of
8 to 12 inches of snow.
SATURDAY AND SUNDAY - A few lingering snow showers are possible
across western Wisconsin on Saturday morning, but otherwise expect
dry conditions with mostly sunny skies. Highs on Saturday will be in
the upper 20s to near 30 with light westerly wind. On Sunday there
will be a few clouds in the sky, and surface winds will be more
southwesterly. This will lead to warmer temperatures, with highs on
Sunday in the mid 30s across the region.
SUNDAY NIGH THROUGH WEDNESDAY - The forecast looks rather quiet.
We`ll see zonal flow aloft develop on Sunday where downsloping flow
on the leeside of the Rockies will warm 850 mb temperatures in the
Central & Northern Plains. This will promote broad, subtle ridging
across the central CONUS early next week. The warmer 850 mb
temperatures signal that warmer temperatures are likely early next
week, as a majority of the guidance continues to show. The new
snowpack has warranted a slight downward adjustment for temperatures
early next week across southern Minnesota, but the warmth will
eventually prevail on Wednesday.
The ridging becomes more pronounced Tuesday afternoon into Wednesday
as low-level southerly flow develops across the Plains. This occurs
in response to an amplified trough over the west coast. With the
southerly flow contributing to strong WAA into the Northern Plains,
forecast models suggest 850 mb temperatures of at least 10C across
the CWA Wednesday. As such, some models have highs Wednesday
approaching (or even exceeding) 60 at MSP. This highlights the
potential of a highly anomalous pattern with potential record
breaking temperatures across the region. We`ve opted to go cooler,
with highs only in the upper 40s and lower 50s on Wednesday. As the
aforementioned trough travels east into the central CONUS, models
depict a surface cyclone rapidly developing somewhere over the
Plains. This system travels northeast Wednesday into Thursday but,
spread between low track and timing within the models is still high.
It seems like we could have another chance at precipitation mid-next
week but exact placement, timing, and type of precip remain large
questions. More certain is cooler weather following the low to close
out the end of next week with a return to near-normal temperatures
forecast.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 640 PM CST Fri Dec 10 2021
Moderate to heavy snow continues across southern/eastern MN into WI
for the next several hours. LIFR conditions expected, but a quick
improvement to VFR will occur soon after the snow ends. Clearing
skies for Saturday with northwest winds shifting southwest in the
afternoon.
KMSP...Snow rates of 1 to 2 inches per hour will continue through
03-04Z, then intensity will slowly taper off in the late evening and
overnight.
/OUTLOOK FOR KMSP/
Sun...VFR. Wind SW 5-10 kts.
Mon...MVFR/IFR in BR/FG possible. Wind E 5 kts.
Tue...MVFR/IFR in BR/FG possible. Wind SE 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Storm Warning until 6 AM CST Saturday for Blue Earth-Brown-
Carver-Dakota-Faribault-Freeborn-Goodhue-Hennepin-Le Sueur-
Martin-McLeod-Nicollet-Ramsey-Rice-Scott-Sibley-Steele-Waseca-
Washington-Watonwan.
Winter Weather Advisory until 6 AM CST Saturday for Anoka-Chisago-
Isanti-Sherburne-Wright.
Winter Storm Warning until 3 AM CST Saturday for Redwood-Renville.
Winter Weather Advisory until 3 AM CST Saturday for Chippewa-
Kandiyohi-Meeker-Yellow Medicine.
WI...Winter Storm Warning until 6 AM CST Saturday for Barron-Chippewa-
Dunn-Eau Claire-Pepin-Pierce-Polk-Rusk-St. Croix.
&&
$$
UPDATE...Borghoff
DISCUSSION...BPH/JRB
AVIATION...Borghoff
...Updated Aviation Forecast Discussion...
.DISCUSSION...
Issued at 306 PM CST Fri Dec 10 2021
The well-advertised winter storm was in progress across the area
this afternoon, with the primary snow band stretching from central
NE into northeast NE and southeast SD and northwest IA as of 3
PM. In addition, some drizzle had developed across eastern
Nebraska and western Iowa, though latest road temperatures across
said area were still in the upper 30s to lower 40s. However, the
colder air is certainly make progress southward, with many spots
dipping down toward freezing, and KOFK and KTQE showing some light
ice accumulation. Given current road temperatures, not
anticipating much in the way of widespread ice accumulation prior
to snow, though still could see some light glaze in some spots,
especially on untreated and elevated surfaces such as bridges and
overpasses.
Going forward, surface low pressure was analyzed over central KS
and will continue its track northeastward this evening, with the
primary precipitation band continuing to overspread the area. CAMs
continue to suggest potential for a narrow enhanced band of
precipitation to the southeast of the main deformation band, which
would likely move through southeast Nebraska during the evening
commute. Looking in a bit more detail, 10.18Z RAP guidance does
show the presence of a frontogenesis/frontolysis "couplet" at 700
mb, which would suggest the CAMs are on to something with that
heavier band. Model soundings do show a shallow dry layer that
would need to be overcome for snow to occur, but given the
strength of the forcing, would think there should be no problem
switching to snow rather quickly. In addition, with the CAMs
hinting at some convective elements, could see some sleet at
times. Finally, should this heavier band play out, surface
temperatures would likely cool slightly faster than previously
thought, meaning any wet roads could become slick with ice and/or
accumulating snow that much faster. Certainly a small scale
feature to keep a very close eye on late this afternoon into early
evening, especially with gusty winds and temperatures cooling
rather quickly below freezing.
As it stands, not much change with snowfall amounts along the
main deformation band, with totals of 5 to 8 inches in far
northeast Nebraska. Amounts will be less as you go south and
should largely be less than 1 inch south of I-80. The main
questions on snowfall totals remain tied to that aforementioned
small-scale banding. Did already increase amounts by an inch or so
within that band, but may need to further increase them this
afternoon. In addition, may need to eventually expand the Winter
Weather Advisory slightly farther south, but confidence in
southern extent of that band is not very high at this time.
Snow should exit east of the area shortly after midnight with
skies clearing out and setting up for a rather sunny weekend.
Temperatures should top out in the 30s and 40s Saturday followed
by 40s and 50s Sunday. Large scale ridging will then build in for
the first part of the work week, with temperatures increasing to
perhaps record levels Tuesday (50s and 60s) and Wednesday (60s to
around 70). While raw model output is quite warm for Wednesday,
there is pretty good agreement of a fairly potent shortwave trough
moving through sometime Wednesday/Wednesday night, which could
lead to increasing clouds or precip which would impact our
temperatures. In addition, that system could bring some rather
diverse weather across the area, with potential for widespread
strong winds, snow in part of the area, and perhaps some
thunderstorms in another part. Plenty of time between now and then
to work out the details, but it does look like it could be our
next chance for impactful weather in the forecast area.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 509 PM CST Fri Dec 10 2021
There likely is patchy freezing drizzle at KLNK with temp of 32,
but transitioning to snow by 00z. And it`s 33 with drizzle at
KOMA, and freezing drizzle may not develop there. Otherwise, IFR
conditions with snow at all TAF locations, along with northerly
winds at 18 to 26 knots. Snow tapers off by 04-07z, and sky
conditions eventually become VFR by 07-09z. Gusts diminish by
09-12z. Storm total snow at KOFK around 2-3", 1-2" at KOMA, and
around an inch at KLNK.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until midnight CST tonight for NEZ015-
018-030>034-042>045-050>053-065-066.
Winter Storm Warning until midnight CST tonight for NEZ011-012-
016-017.
IA...Winter Weather Advisory until midnight CST tonight for IAZ043-
055-056-069.
&&
$$
DISCUSSION...CA
AVIATION...DeWald