Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/10/21
Area Forecast Discussion
National Weather Service La Crosse WI
958 PM CST Thu Dec 9 2021
.UPDATE...
Issued at 955 PM CST Thu Dec 9 2021
A dynamic forecast continues to transpire for Friday afternoon`s
and night`s winter storm as increasing CAM guidance arrives. Major
changes to the headlines included the backing up of the
warning/advisory for much of the day on Friday as the available
CAM guidance all tracks the leading def zone precipitation wing
further to the north, leaving much of the area dry through the
early to mid afternoon. Added Clayton and Fayette to the advisory
as the loss of ice in the dry slot and ongoing surface CAA may
lead to the development of freezing drizzle late Friday night. May
need to add Grant County as well, but confidence in impacts was
not as high given the longer persistence of the warmer surface
airmass. Also nudged the warm nose further north with the
continued northward shift in the track, with the threat for
freezing rain knocking on La Crosse`s door Friday evening.
Finally, added the mention of thundersnow to the forecast with a
solid region of negative EPV or even pure upright instability
noted in CAM/CPM soundings within the band of heaviest snow.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 205 PM CST Thu Dec 9 2021
Attention squarely focused on the upcoming winter storm. Water
vapor satellite shows the system taking shape over the Desert
Southwest and this will take a northeast track coming across the
region with a positive tilt Friday night. The precipitation looks
to be focused in the three time frames, initial band comes in
Friday morning, second looks to be later Friday afternoon into the
first part of the evening followed by a third round late Friday
evening into the overnight. The first round looks to be primarily
forced by a band of moderate mid-level frontogenesis in the
750-600 mb layer that comes across central/southern Minnesota into
northern/central Wisconsin. The second round looks to have the
strongest period of forcing with it. Another band of moderate to
strong mid-level frontogenesis looks to take shape in the 750-500
mb layer, positioned a bit farther south over southern Minnesota
into western and north-central Wisconsin. This lift from this
frontogenesis will be aided by strong up glide on the 285K
isentropic surface along with good jet dynamics in the right
entrance region of the a departing 300 mb jet streak and in the
left exit region of the next incoming jet streak. This is when the
09.12Z HREF probabilities for greater than one inch an hour
snowfall rates jump into 70 to 90 range with a small signal for
some rates to exceed 2 inches an hour. This round of forcing looks
to be off during the mid-evening hours only to be replaced by yet
another mid-level frontogenesis in the 700-550 mb layer late
Friday evening which again looks to mainly be over southeast
Minnesota into western and north-central Wisconsin. The HREF also
shows some potential for this band to hourly rates in excess of 1
inch but the probabilities are lower, generally in the 20 to 30
range. The heavy snow band will set up underneath this round of
forcing with the highest confidence of amounts exceeding warning
criteria from southeast Minnesota into western and north-central
Wisconsin. Some potential that there could also be some convective
snows in the heavy snow band with the RAP showing a bit of
slantwise instability above the frontogenesis bands. If this were
to occur, the potential for hourly rates to exceed to 2 inches
will jump up dramatically.
South of the main snow band, the precipitation types get to be a
bit more dicey. Forecast soundings show a distinct warm nose aloft
working in that would be enough to cause partial to complete
melting. This will set up a zone of mixed precipitation where some
sleet and freezing rain could occur. Output from the HREF does
suggest the possibility of some minor ice accumulations across
northeast Iowa into southwest Wisconsin.
The Winter Storm Watch has been converted over the warnings and
advisories this afternoon. Much of the watch along the
Iowa/Minnesota border in the Interstate 90 corridor in western
Wisconsin has been upgraded to a warning. Band of heaviest snow is
expected from about Dodge County Minnesota over the Clark County
Wisconsin where some totals could exceed a foot. Farther south,
the watch has been upgraded to an advisory for a few counties in
northeast Iowa and southwest Wisconsin where snow amounts will not
be as high but a better potential for the wintry mix to occur.
.LONG TERM...(Friday night through Thursday)
Issued at 205 PM CST Thu Dec 9 2021
Taking a quick look out into next week, there looks to be the
potential for another storm to impact the region around the middle
part of the work week. Current indications suggest this system
will take a more northwest track putting the local area into the
warm sector. The 09.00Z NAEFS indicates the potential for
temperatures at 700 and 850 mb to be 1 to 2 standard deviation
above normal which would push surface temperatures in the 40s and
50s. Some spots could even reach the lower 60s! This system also
looks to have the potential to bring a pretty good slug of
moisture with it. Again looking at the NAEFS data, both the
precipitable water and specific humidity could be in the 4 to 5
standard deviations above normal range. At this time, looks to be
a warm, rainy system falling on top of the existing snow pack.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 533 PM CST Thu Dec 9 2021
An initial band of 600 to 700 mb frontogenesis will produce some
light snow at KRST by 10.16z. The snow will then pick up intensity
between 10.20z and 10.22z. Snowfall amounts by evening will be in
the 2-4 inch range. Most of this snow will fall after 10.20z. The
total snowfall amount by Saturday morning will likely range from 9
to 13 inches.
Meanwhile, at KLSE the snow will likely not accumulate until after
10.21z. Snow amounts between 10.21z and 11.00z will likely range
between 1 and 2 inches. May also have watch for a wintry mix, but
confidence was not high enough to include at this time. he
total snowfall amount by Saturday morning will likely range from 5
to 9 inches. If more of wintry mix occurs, these totals may be on
the lower end.
Once the snow starts to accumulate, ceilings and visibilities
will quickly become IFR/MVFR.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 PM Friday to 6 AM CST Saturday
for WIZ054-055.
Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for
WIZ041>044-053.
Winter Storm Warning from noon Friday to 6 AM CST Saturday for
WIZ017-029-032>034.
MN...Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for
MNZ095-096.
Winter Storm Warning from 9 AM Friday to 6 AM CST Saturday for
MNZ079-086-087.
Winter Storm Warning from noon Friday to 6 AM CST Saturday for
MNZ088-094.
IA...Winter Weather Advisory from 3 PM Friday to 6 AM CST Saturday
for IAZ010-011-018-019-029-030.
Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for
IAZ008-009.
&&
$$
UPDATE...Skow
SHORT TERM...04
LONG TERM...04
AVIATION...Boyne
Area Forecast Discussion
National Weather Service Denver/Boulder CO
836 PM MST Thu Dec 9 2021
.UPDATE...
Issued at 808 PM MST Thu Dec 9 2021
Water vapor shows a steady plume of moisture going over western
Colorado which is producing snowfall in the mountains this
evening. The forecast for the mountains remains on track with the
Park Range and Rocky Mountain National Park receiving the highest
totals. There is plenty of clearing from South Park to Denver to
Sterling and areas southeast this evening with no snow expected
through much of the night. A cold front will move southward out of
Wyoming overnight tonight which will eventually moisten the low
levels. The latest model guidance has come in drier than the
previous runs on the CAMs. The HRRR barely shows an upslope
component to the wind across the I-25 corridor and has basically
no snow accumulation for that area. The NAM and NAM Nest have
taken away snowfall in the 00Z runs. On the contrary, the 18Z
global ensembles continue to have 80-90 percent of the members
showing accumulating snow at DIA. In summary, the upslope flow
looks bleak for the I-25 corridor to receive snowfall but a jet
streak overhead with ample moisture aloft will typically produce
something in our area. PoPs were lowered slightly across the
Denver metro and Palmer Divide tomorrow morning but the overall
forecast of a trace to inch of accumulation remains the same.
There is low confidence in whether the snowfall will impact the
morning commute but the chance of poor travel conditions in the
morning seem to be decreasing.
&&
.SHORT TERM...(This evening through Friday)
Issued at 241 PM MST Thu Dec 9 2021
A strong moist southwest flow aloft ahead of an upper level
trough over California will bring heavy snow to the western and
northern mountains tonight. Based on water vapor satellite imagery
and radar, best moisture is just arriving to the northern
mountains. An additional 8 to 16 inches are expected for the
northern mountains. Over the Park range in western Jackson county
an additional 2 feet of snow will be possible. The I-70 corridor
east of Vail Pass will be somewhat sheltered from the heavier
snowfall while southwest flow aloft prevails. The upper level
trough weakens and quickly moves eastward overnight. Once the
trough axis shifts east of the mountains, better orographic lift
will prevail for the I-70 corridor. Light snow fall is expected to
prevail for most of Friday under west to northwest flow aloft.
Will continue with the Winter Storm Warning for the northern
mountains. For the mountains east of Vail Pass, the Winter Weather
Advisory will remain in effect where 4 to 10 inches of snow will
be possible. If traveling in the mountains tonight and Friday
expect snow covered roads and hazardous travel conditions.
For the foothills, Urban Corridor, and eastern plains, expect
cloudy skies, but dry conditions to prevail for most of the night.
A cold front pushes south through eastern Colorado after
midnight, ushering in colder air for Friday. The air behind the
front will be cold enough for all precipitation to fall as snow.
Lift from the trough, right entrance region of the jet, and
upslope slope flow is expected to produce a period of snow Friday
morning. Snowfall amounts are expected to be light with most
locations seeing less than an inch. Could see a little more snow
along the Palmer Divide. Northern areas from Fort Collins to Fort
Morgan could miss out on the snow due to the northerly downslope
component off the Cheyenne Ridge.
.LONG TERM...(Friday night through Thursday)
Issued at 241 PM MST Thu Dec 9 2021
Mountain snowfall will continue to wind down through the
overnight hours with west/northwest flow aloft. A few of the
favored northwest aspects in the Park Range could pick up another
couple of inches of snow overnight with little to no additional
accumulation elsewhere. Most snow should end by about midnight as
a large area of subsidence spreads across the region. Gusty winds
will continue across the high terrain tomorrow night with perhaps
a weak mountain wave developing in the 40-50kt cross-barrier flow.
An upper level ridge will begin to build this weekend as a drier
pattern returns. Temperatures will rebound a bit on Saturday with
highs in the upper 40s across the plains, aided by light downslope
westerly winds. Cooler air should stay trapped across the high
country with highs still in the upper 20s to low 30s for the
mountain valleys. Gusty winds are likely to continue for the
higher elevations with some gusts up to 50-55 mph possible.
We should return to a pattern of well above normal temperatures
Sunday through the first half of next week. A robust ridge is
expected to develop across the Central Great Plains/Mid-
Mississippi Valley region by the start of next week. 500mb Heights
from the NAEFS and ECME are above the maximum values in
climatology across those areas for a remarkably long period of
time. On our side of the ridge, warm southwesterly flow will lead
to temperatures reaching the low 60s both Monday and Tuesday.
By mid-week uncertainty in the forecast increases substantially
as a potent trough approaches from the Pacific coast. Models are
in good agreement that this trough axis should arrive by
Wednesday, but beyond that details are hazy. The overall pattern
would favor a quick moving snowfall across the western slopes
while most of the plains stay dry. The main impacts across the
Front Range and plains would likely be winds. The 12z GFS reflects
a higher end wind event across the forecast area with a nearly
textbook setup for a strong mountain wave with a stout stable
layer just above the ridgetop along with 70-110kt cross barrier
flow between 700mb and 500mb. The position of the trough is less
favorable among the other global models, but at the very least the
potential for strong winds/elevated fire danger should be watched
closely over the next few days.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 808 PM MST Thu Dec 9 2021
Ceilings will lower after a cold front moves through around 9-10Z
tonight. There may be some snow showers that develop behind this
front from roughly 12-16Z but the chances of this seem to be
lowering. The biggest impact during the afternoon will be strong
northwesterly winds that develop with gusts up to 38 knots
possible.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Friday for COZ034.
Winter Storm Warning until 5 PM MST Friday for COZ031-033.
&&
$$
UPDATE...Danielson
SHORT TERM...Meier
LONG TERM...Hiris
AVIATION...Danielson
Area Forecast Discussion
National Weather Service Cleveland OH
939 PM EST Thu Dec 9 2021
.SYNOPSIS...
High pressure will move off the east coast overnight as an upper
level system moves through the upper lakes. Low pressure will
develop over the Central Plains on Friday and deepen and track
into the northern lakes Friday night and Saturday. High pressure
will build into the region early next week.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
Starting to see some indications of patchy dense fog and low
stratus developing late tonight into Friday morning as low level
moisture significantly increases with warm air advection. The
best chance of dense fog will be in western and southern zones
where winds may become light enough for fog development. Will
need to monitor for potential fog related headlines overnight,
but opted to only mention the hazard in the HWO until confidence
increases. A more optimistic outcome will occur if winds do not
decrease overnight. No other changes needed with this update.
Previous Discussion...
Rather abrupt changes are expected in the weather during this
period with a quick warm up with storms followed by rapid windy
cooling on Saturday.
Into Friday we can expect rather quiet weather as high pressure
moves off the east coast and a southerly flow prevails. A short
wave will lift northeast of the Great Lakes this evening. Very
light precipitation associated with this feature will move
through the area this evening with a little precipitation which
is mostly aloft that may produce a few sprinkles or flurries.
Once that feature lifts to the northeast our attention focuses
on the developing low pressure over the plains that is expected
to deepen and move into the Great Lakes Friday night and
Saturday. Very strong wind fields are associated with this low
pressure. Initially warmer and increasingly humid air will be
drawn into the region Friday night with dewpoints rising to
55-60F by Saturday morning. Modest amounts of CAPE in the
200-400 J/KG range with rather intense wind shear is expected
from 06Z to 12-15Z ahead of a cold front that is expected to
sweep east through the region on Saturday. SPC extended the risk
of severe weather northward into the southwest portion of the
region and that looks reasonable. Some experimental guidance
that processes the HRRR model called the NCAR Neural Network
convective Hazard Forecasts indicates a high likelihood of
severe weather across the western and central part of the CWA
before 12Z Saturday and over the eastern third of the area
between 12Z-15Z. There is some potential for tornadoes given the
high shear low CAPE situation.
Following the cold front passage, cold advection will overspread
the region with rapidly falling temperatures from the 60-65
degree range. Strong winds will mix down to the surface and a
wind headline will likely be needed post frontal for several
hours. The showers and storms will quickly exit the region after
the frontal passage and there could be more precipitation
toward dark as temperatures drop into the 30s.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
After analyzing the latest 18z high resolution model guidance, we
have issued a High Wind Watch for the lakeshore areas of northern
Ohio Saturday morning through Saturday evening. The potential of
damaging wind gusts up 60 or 65 mph is increasing along and behind a
cold front on Saturday. The highest wind gust threat will be closer
to the lakeshore and on top of hilly terrain.
Previous Discussion...
Post frontal environment leaves the region in diminishing winds as
the low pressure system lifts out to the northeast and the front
heads for the east coast. As strong as the system was, being Pacific
in nature, the cold air advection will not be all that impactful.
Temperatures on the back side will be in the 40s for the most part,
and there will be a noticeable lack of lake effect. Skies clear and
winds continue to subside into Sunday night as high pressure builds
to the south over the Ohio Valley.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
Upper level ridge begins to build over the northern Gulf Coast into
the middle of next week, signifying increasing heights into our
region and resulting in a warm up once again. Models indicating
disturbance riding around the top of the ridge, and will see low
POPs enter the picture. There could also be a warm front during this
period of time as well extending from the next surface low
developing in the lee of the northern Rockies. Thursday temperatures
could be pushing the 60 degree mark again.
&&
.AVIATION /00Z Friday THROUGH Tuesday/...
VFR conditions continue for the next several hours, but expect
southerly flow to usher a surge of moisture into the local area
overnight into Friday. Deteriorating ceilings will spread
northeast across the area after around 06Z tonight. Low stratus
and fog will likely produce IFR to LIFR ceilings and
visibilities at KTOL/KFDY/KMFD for much of the day Friday, and
can`t rule out similar conditions at KCLE/KCAK for the same
timeframe. Showers will begin to move northeast into the area on
Friday evening, but the best chance of rain will likely occur
after the TAF period.
Winds will generally be out of the southeast at 8 to 14 knots
tonight, but western terminals may become more light and
variable overnight. Winds become southerly to southwesterly on
Friday. Will need to monitor for some gusty downslope winds to
25 to 30 knots at KERI overnight into Friday morning. LLWS may
develop towards the end of the TAF period, but not confident
enough to add into this update.
Outlook...Non-VFR likely in showers/storms Friday evening into
Saturday morning. Strong wind gusts are expected with the
approach and passage of a cold front on Saturday.
&&
.MARINE...
Gale Watch and Storm Watch Saturday into early Saturday night.
Offshore wind flows ahead of the next frontal system, which will
quite powerful as it approaches the region. Winds really begin to
ramp up Friday night in the warm sector where winds will veer from
SE to SW. Cold front expected to enter the western basin after 15Z
Saturday, and will have exited by 21Z Saturday. There will not be
much of a notable wind switch with the passage of the front, but
sustained 20-25kt winds ahead of the cold front will become greater
than 40kt sustained winds in the wake of it for Saturday afternoon
into early Saturday night. As mentioned, Gale Watches in effect, and
a Storm watch for the eastern basin of Lake Erie. Waves in the
central basin eastward are expected to exceed 12ft, possibly as high
as 18ft. Waves fall below 10ft basin wide after 06Z Sunday and winds
below 20kts by 12Z Sunday.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...High Wind Watch from Saturday morning through Saturday evening
for OHZ003-007>012-089.
PA...High Wind Watch from Saturday afternoon through Saturday
evening for PAZ001.
MARINE...Gale Watch from Saturday morning through Saturday evening for
LEZ142>144-162>164.
Gale Watch from Saturday morning through Saturday evening for
LEZ145>148-165>168.
Storm Watch from Saturday afternoon through Saturday evening
for LEZ149-169.
&&
$$
SYNOPSIS...LaPlante
NEAR TERM...LaPlante/Maines
SHORT TERM...26
LONG TERM...26
AVIATION...Maines
MARINE...26
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
957 PM EST Thu Dec 9 2021
.SYNOPSIS...
A weak disturbance will bring some very light snow to the region
on Friday before we await a more significant system...which
will arrive on Saturday. This storm will bring a period of
freezing rain that will change to rain as temperatures warm
during the day Saturday. Temperatures will continue to warm
Saturday evening before a cold front sweeps through the area
Saturday night with gusty winds and seasonably mild temperatures
for Sunday. Temperatures remain above normal through much of
next week with dry weather expected through Wednesday.
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Update...Currently a rather robust looking regional radar mosaic
showing the narrow band of snow forecast to cross the area
tonight is not doing a whole lot at the surface. It is a
struggle to find many automated obs of snow...let alone any
appreciable accumulation. However snowfall is forecast to pick
up in intensity...especially E of Lake Ontario...so I do not see
any reason to deviate significantly from the previous forecast.
The best chances of snow amounts approaching 1 inch will be in
the mtns where upslope may enhance lift and along the Midcoast
where some ocean effect may work inland for a time as flow
reverses.
Previous discussion...A few scattered instability flurries and
snow showers will diminish soon after sunset, except across the
mountains where they`ll likely linger into the evening. High
clouds from our next system are already moving into southwest
New Hampshire, and will continue to progress across northern New
England overnight tonight. Temperatures will mostly fall this
evening and then stabilize once the cloud cover thickens.
Northern and eastern areas will be the last to see the clouds
arrive, and are therefore expected to be the coolest.
Warmer air is already starting to move in aloft, and this trend will
continue through the overnight hours. With this warm air advection,
a band of light snow will likely progress northeastward into New
Hampshire toward daybreak. Overall the best chances for snow are
across northern and western New Hampshire overnight tonight where
snow showers are likely, with decreasing chances toward the
Seacoast.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
The band of snow showers will continue to progress into Maine
tomorrow morning. Precip will mostly shut off across New Hampshire
by mid morning. Accumulations near an inch are possible across
northern areas and the higher terrain, but elsewhere generally a
half inch or less are expected.
The band of snow showers will progress through Maine during the
daylight hours tomorrow morning. Similarly to New Hampshire,
accumulations near an inch are possible across the northern areas of
Maine, while generally lighter amounts are expected elsewhere. The
one exception to this may be along the Maine MidCoast.
High res guidance on the NAM 3km and HRRR has consistently been
hinting at some ocean enhancement of snow along parts of the
MidCoast. A weak area of convergence offshore will likely serve as
the focus for some ocean effect snow showers. With the difference
between sea surface and 850mb temps between 17C to 20C tomorrow
morning, greater than the 13C absolute instability benchmark, it
looks likely that these snow showers will develop. Whether or not
they make it onshore is the biggest question, but there is fairly
good agreement among the high res guidance that they will as
winds turn onshore. This would enhance the snow totals along
parts of the MidCoast, with the Camden Hills area standing the
best chance to pick up 1-2 inches of snow.
Also during the day tomorrow, cold air damming looks like it will
begin to dig in its` heels across the region. After an initial push
of mild air off the ocean sends temps into the upper 30s along the
coastline, light northerly winds from high departing high pressure
across the Canadian Maritimes will likely thwart the warm air and
keep temperatures locked in the 20s and low 30s from late
tomorrow afternoon through the overnight hours. During the
initial warm up some light rain and snow showers are possible
near the coast, but by the overnight hours tomorrow the precip
types will likely become either rain, freezing rain, or sleet.
A dry period is likely later tomorrow afternoon into the overnight
hours. But after midnight more showery precipitation is likely to
begin moving in and bring some light mixed precipitation after
midnight. Chances will continue to increase toward daybreak Saturday
morning as the cold airmass gradually moderates toward freezing.
Overall precip amounts greater than a few hundredths will
likely hold off until daybreak on Saturday, but some light
coatings of ice are possible before this time, especially across
southern New Hampshire.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
High Impact Weather Potential:
* A period of freezing rain primarily Saturday morning will bring
travel impacts.
* Gusty winds late Saturday night into Sunday.
* No significant weather impacts beyond Sunday.
--Pattern and Implications--
Strong jet over the eastern Pacific early this afternoon /+EPO/ with
little downstream blocking east of the region /+NAO/ will allow for
a progressive pattern through the long term forecast period. +EPO
correlates to warmth over the northeastern United States given the
ample amount of Pacific air that will be present over the lower 48
and that is evident in the deterministic and ensemble guidance which
favors at or above normal high temperatures throughout the entire
long term forecast period. As for sensible weather...pretty much
the entirety of the weather impacts will come to open the period
Saturday and Saturday night as a Great Lakes low pressure system
passes well north of the forecast area dragging a cold front through
the region Saturday night. High pressure largely dominates the
Sunday-Wednesday period with another frontal system approaching the
region to end the forecast period Thursday.
--Daily Details--
Saturday - Saturday Night: The period opens with low pressure over
lower Michigan deepening about 10mb in 12 hours as it moves
northeast through the day. Surface pattern looks similar to the
event on Monday...but the overall airmass aloft will be
significantly warmer...roughly 5C warmer at H8. By 18Z Saturday T8s
push above +10C with model soundings suggesting +10C air existing in
a deep layer from 800mb to 925 mb. As we start to get some high
resolution model output for this period...the overall trend is for
ankle-deep cold air to hold very persistently for areas south of the
mountains through the day and given this trend /which matches
pattern recognition/ have continued to trend temperatures downward.
However...with the amount of warm air aloft...expect temperatures to
be higher than our Monday event which will likely leave many
locations in the 30s for much of the day...but too warm to support
significant freezing rain. Guidance supports two rounds of
precipitation...one along the advancing warm front in the morning
before a potential break Saturday evening before the cold front
arrives overnight Saturday night. Can/t rule out a rumble of
thunder along the front Saturday evening with some elevated parcels
seeing 100-200 J/kg of CAPE. Beyond the front...attention will turn
to the winds in strengthening cold advection scenario as isallobaric
component lines up well after midnight with 40kt at H9
suggesting gusts 30-40 mph are possible.
Ice Amounts: Expect any icing across the southern half of NH to be
over early /7-8am/ with no more than very light coating. Given the
QPF uncertainty...it is possible that temperatures rise before
meaningful precipitation arrives. Further north and
east...however...confidence is increasing in a short period of
freezing rain before temperatures move into the mid 30s. Generally
0.10" of icing or less...which suggests travel as the primary impact
Travel impacts look to be confined to the morning with nearly all
areas above freezing /though still in the 30s/ in the afternoon.
Expect winter weather advisories will be needed for some of the
area...but will await increasing confidence in precip
timing/location before issuing. Will continue to message this
potential in the afternoon Hazardous Weather Outlook.
QPF: Progressive warm and cold frontal passages will limit overall
precipitation potential despite PWATs moving above 1.25" as the
elevated warm front lifts north of the region. Mesoscale guidance
/09.12Z NAM Nest...NAM and RGEM/ is coming in drier than the global
guidance...with the best totals over the mountains where the
advancing warm front is best aligned with mid level forcing. Have
trended the forecast a bit in this drier direction...generally 0.40-
0.80 from south to north.
Sunday - Monday: Quick shot of cold air arrives Sunday behind
departing cold front with a blustery and somewhat cooler /though not
cold/ day expected. T8s fall back to around -8C in the post frontal
airmass. Model soundings suggest that we will be close to mixing to
H8...which would allow high temps to reach into the lower to perhaps
middle 40s from the coast into the foothills...with 30s expected in
the mountains. Arriving airmass will be dry...with any residual
mountain snow showers coming to and end. Model profiles indicate
around 35kt of flow at the top of the mixed layer, so wind gusts
over 30 mph are likely. High pressure settles south of the region
for Monday with a substantial gradient remaining overhead though now
in a warm advection regime. Expect highs mostly in the 40s with a
few lower 50s possible over the south as shallower mixing will
offset some of the increasing warmth in the column.
Tuesday - Wednesday: Flow over North America gradually amplifies
with a longwave ridge axis taking shape from Hudson Bay south
through the Appalachians. With the mid level ridge axis to our
west...this keeps our area susceptible to impacts from the northern
stream and ensemble +T8 anomalies actually decrease from Monday into
the midweek as models hint at a dry cold frontal passage sometime on
Tuesday. T9s look to remain similar on Tuesday as Monday...then
fall behind the front back to the negative single digits on
Wednesday. This should take highs down about 5 degrees from the
upper 30s to upper 40s from north to south on Tuesday to the mid 30s
to mid 40s on Wednesday with continued dry conditions. Northwest
winds will continue...though somewhat lighter than earlier in the
week.
Thursday: High pressure ridge axis begins to push east of our
longitude as we reach the end of the long term forecast period on
Thursday. This should allow for renewed warm advection with modest
ensemble agreement that another low pressure system will track into
the Great Lakes region with some potential for warm frontal
precipitation to impact our area. Best ensemble support for
precipitation at this range is in the mountains and will follow the
National Blend of Models depiction in this regard. As for
temperatures...the overall consensus is that the greatest positive
temperature and height anomalies arrive at the end of the week and
will therefore push temperatures upward with mid 40s to mid 50s from
north to south and can make further adjustments from here.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Short Term... VFR conditions will gradually deteriorate to MVFR
or IFR toward daybreak tomorrow. IFR conditions are expected
across northern and eastern terminals tomorrow, with MVFR
ceilings across southern terminals. A few hours of light snow is
possible tomorrow morning, which could reduce visibility to IFR
briefly. Ceilings will linger near MVFR into tomorrow night,
and then fall to IFR with lowering ceilings and possible fog.
Light freezing is also possible late tomorrow night.
Long Term...Widespread LIFR/IFR in stratus/fog with early
morning freezing rain changing to rain. Rain...with a few
embedded rumbles of thunder is possible Saturday night with
conditions improving to VFR with strong westerly winds /gusts
over 30kt/ developing and continuing through the day on Sunday.
VFR Monday-Tuesday with moderate westerly winds continuing.
&&
.MARINE...
Short Term... High pressure will lead to diminishing seas and
winds tonight through tomorrow. Seas will begin to build again
tomorrow night ahead of an approaching low pressure center.
Long Term...Southerly winds strengthen on Saturday with gale
force gusts possible by evening. Winds shift westerly with gusts
to gale force likely continuing through Sunday. In coordination
with neighbors...have issued a gale watch for the period of
highest winds late Saturday through Sunday. Small crafts will
likely be needed for Monday and possibly Tuesday as westerly
winds gradually diminish and waves subside.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Gale Watch from Saturday afternoon through Sunday afternoon
for ANZ150>154.
&&
$$
NEAR TERM...Legro
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
852 PM EST Thu Dec 9 2021
.SYNOPSIS...
Mainly dry conditions are expected tonight, with a few
sprinkles possible from time to time. Warmer temperatures will
overspread the region Friday and Friday night, with showers and
storms expected Friday night through Saturday morning. Windy
conditions are expected Saturday before cooler and calmer
conditions evolve for Saturday night into Sunday. A slow warming
trend is once again expected early next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Plentiful moisture is advecting NNE through the Ohio Valley this
evening, and there is evidence of a sharp gradient in
temperature at the surface -- with 8PM readings of 56 at CVG and
46 at DAY. This is a fairly strong setup for fog development
later tonight, as this moisture leads to saturation on the
cooler side of the surface boundary. HRRR visibility plots
remain very aggressive in developing fog (likely dense in spots)
during the 06Z-12Z time frame from southern Illinois through
western and central Ohio. This remains the primary concern for
the overnight hours, and fog potential has been expanded
slightly in the grids to account for it. Temperatures were also
adjusted, to show a sharper gradient than before -- slightly
cooler values in the northern and northeastern ILN CWA, and
slightly warmer values in the southwest.
Predictive dense fog advisories are always a significant
challenge, but the evolution of upstream observations over the
next 4-6 hours will be crucial in determining how things may
develop over the ILN forecast area closer to daybreak.
Previous discussion >
Mid/high level clouds are gradually pulling away from the
region this afternoon, with some light echoes still appearing
on regional mosaic radar imagery. Quite a bit of LL dry air
sampled on the KILN 09.12Z RAOB, and am not seeing any sites
reporting pcpn reaching the ground, so anticipate that we may
see more of a virga situation for this afternoon with just a
small chance for a few sprinkles as we progress into the evening
hours. However, most spots will remain dry. In fact, are seeing
skies trend clearer briefly for late afternoon into early
evening, especially for locations south of I-70, before the
onset of more robust LL moisture advection begins late this
evening through the overnight.
Are already seeing the manifestation of an more potent LLJ
nosing north into the region with a surge of LL moisture back
across IL/IN. Will see this moisture advection continue to
expand N/NE into the ILN FA by mid/late evening, with OVC
conditions settling in area-wide for the overnight period. In
fact, will see setup evolve by late tonight into Friday
morning that suggests the potential for some fog development,
especially west of I-75 into parts of IN where the LL moisture
advection will be the strongest. Could even see some patchy fog
linger into the afternoon on Friday with a rather soupy setup
until eventually the LL thermal gradient is pulled far enough
north and enough mixing can start to take place by the evening
Friday. Lows tonight will range from the upper 40s in N KY to
lower 40s in central OH.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
We will likely be contending with quite a bit of cloud cover and
even some fog Friday morning into the afternoon before
eventually enough mixing can take place for the VSBYs to improve
by later in the day. The OVC conditions will inhibit temps from
warming too quickly, especially through early afternoon, with
daytime highs ranging from near 60 degrees in N KY to the upper
40s in central OH. These temps will continue to rise through
the evening and overnight ahead of the impending system set to
impact the region Friday night into the day on Saturday.
Broad/large-scale troughing across the central CONUS will promote SW
flow aloft from the s-cntrl plains to the OH Vly early Friday
with stronger deep-layer WAA to becoming during the daytime.
Lee side cyclogenesis will be underway by early Friday in the s-
cntrl plains, with the attendant theta-e boundary arcing to the NE
across the mid MS/OH Rvr Vlys early in the day. With the deepening
of the system as it ejects east into the mid MS Rvr Vly by Friday
evening, will see robust theta-e advection begin to evolve by late
in the day into the overnight near/E of the MS Rvr. This will place
the local area well within the broadening open warm sector of the
system, with tremendous moisture and mass transport north into the
region by late in the day through the evening hours. Moisture depth
will initially be rather shallow in nature during the heart of the
morning and afternoon hours on Friday (likely indicating a
fog/drizzle potential moreso than anything else, especially
through about 21z. Have kept PoPs largely in the chance
category until mid afternoon before the depth of moisture
availability becomes such that the isentropic lift is able to
generate a NW to SE band of SHRA, which will pivot NE, mainly
for areas NW of I-71, during the late afternoon and early
evening.
At this juncture, we shift our focus to Friday night into the day on
Saturday -- a setup that continues to be concerning for the
region. There are several items to break down as we discuss the
expected evolution and potential impacts locally, so an attempt
to do so follows here:
We have just reached the time window for which we can analyze
some of the various CAM solutions. And one thing that continues
to stick out, from a CAM /and/ a synoptic-based deterministic
and ensemble perspective, is the depiction of a stronger/deeper
system, which in turn would make the overall progression of it
eastward... a bit slower. This trend is significant for several
reasons, most notably a corresponding depiction of slightly
stronger LL wind fields (and corresponding LLJ maxes), as well
as an indication that the threat for strong to severe storms
will linger past daybreak on Saturday.
This is a climatologically-favorable track that is /generally/
supportive of a severe threat across parts of the OH Vly. A
slowly-deepening sfc low is fcst to track from N MO to Lake
Michigan from Friday afternoon into Friday night. Deep lows on
this track have a rather long history of being supportive for at
least some severe weather across the OH Vly. And although the
low will be pulling away/N through MI by the time the FROPA
actually occurs locally late Saturday morning, it will continue
to deepen as it does so. Both deterministic and ensemble
solutions have trended toward a deeper system, with the prospect
of a sub-985mb low in MI Saturday morning seeming more and more
likely. The overall track and deepening of the sfc low as it
progresses from MO to MI puts the region squarely in a favorable
zone for robust isallobaric and LL mass field response, aiding
in enhanced convergence and large-scale ascent, especially after
06z. And with this track and a very favorable dynamic and
kinematic environment, traditional thermodynamic evolution, such
as instby, tends to become slightly less important as the mass
transport/response can often be sufficient to produce strongly-
forced vertical ascent amidst an increasingly-frontogenetic
response.
Looking more closely at some of the ingredients... the effective
shear of 50+ kts will be /more/ than supportive of storm
organization, likely manifesting itself in a SSW-NNE linear
convective structure for the overnight period, especially
considering the /largely/ unidirectional profile with favorable
vertical speed shear in place. A /very/ robust H9 LLJ of
45-50kts and H8 LLJ of 60-65+ kts will overspread the ILN FA
toward midnight and beyond, supporting tremendous LL mass
response and ascent. It does appear there will be at least
/some/ cross component of the LL bulk shear vector to the front
itself, helping enhance LL shear and SRH, supporting
circulations within any QLCS structure that is able to develop
(likely closer to the front very late in the night). Anticipate
that the magnitude of the LL shear (45-50kts) may be sufficient
to overcome the larger angular overlap with the initiating
boundary. As for the instby... this may be one of the main
limiting factors, despite the impressive theta-e advection/LL
moisture transport north into the area ahead of the front (with
sfc DPs in the upper 50s and lower 60s and PWATS approaching
250-300% of seasonal norms). It is likely that one or more
convective lines may develop along a pre-frontal trough or LL
confluence axis, initially to the west of the ILN FA, with the
front itself hanging back even further to the west across MO
after midnight. Synoptic-based deterministic and ensemble
guidance continues to depict a narrow ribbon of several hundred
J/kg SBCAPE nosing north into IN and parts of N KY and W OH
after 06z. This narrow ribbon of slightly more favorable
thermodynamics will likely overlap, at least in a small spatial
and temporal capacity, with the most favorable kinematic
environment in place as the core of the strongest H8/H9 LLJs
translates NE through the region between 06z-12z.
Regarding storm evolution, there remains some uncertainty at
this juncture regarding the coverage /and intensity/ of
prefrontal activity in the 06z-12z time frame. Sounding analysis
from a variety of synoptic and CAM guidance suggests that a LL
isothermal layer or cap may remain in place across parts of the
area through at least 08z (and perhaps even several hours
longer). Eventually, the strong forcing and large-scale ascent
will be enough to overcome this, allowing for convection to
become more surface-based as we progress later into the night
and beyond. If /and this remains a BIG IF at this juncture/ the
prefrontal activity is able to become more sfc-based between
08z-12z, the severe threat would likely be maximized a bit
earlier (opposed to just along/ahead of the front itself).
So taking this all in from strictly a setup and ingredients-
based fcst perspective, there is certainly some concern that the
OH Vly may be subjected to one or more slightly elevated (or
even surface based) rotating clusters before daybreak and morning
QLCS (around/after daybreak). At this juncture, strong
straight- line winds will remain the primary concern, but any
convectively- driven sfc wave development could allow (with some
favorable LL shear orientation as well as some brief backing of
the winds), for circulations to develop with any activity that
moves through. This would indicate a tornado potential in the
ILN FA, at least in a small spatiotemporal manner. Will continue
to highlight this threat in the HWO, and could very well see
/additional/ upgrades/expansion of SPC convective outlooks to
encompass more of the ILN FA as we get closer to Friday night
and we have a better look at some of the CAM guidance and can
further hone in on the timing and overlap of parameter spaces.
The other item, and it is not an insignificant one, will be the
robust synoptic-based winds Friday night and especially during
the day on Saturday. With the trend of a stronger system, it is
appearing more and more likely that a Wind Advisory will
eventually be needed for parts of the ILN FA, mainly for the
daytime Saturday. In the WAA advection Friday night ahead of
the FROPA, could very well see sustained winds of 20-25kts,
especially near/N of I-70, which in-and-of itself would be close
to advisory-level criteria. Behind the front during the
day/afternoon on Saturday, within the increasingly-well mixed
BL environment, we could see gusts 30-40+ kts at times, again
favored for locations further north. A stronger and slightly
slower system evolution would naturally favor more enhanced
synoptic-scale wind/gusts on Saturday, with indications for 40+
kts very possible across parts of the area. Additionally, with a
very moist and strongly- forced environment, any training
convective activity may yield localized flooding, despite the
progressive nature of the system as a whole. With /some/ overlap
between the steering- layer flow and the initiating boundary,
some briefing training of activity will be possible, even with
individual elements moving quickly within the overall evolution.
However, anticipate the overall flood/flash flood threat will
be limited and isolated in nature.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
High pressure southwest of the region will build into KY on Sunday
with southwest flow over much of the region. This will limit the
strength of the cold air in the post-frontal atmosphere and
permit Sunday`s highs to reach into the mid 40s. Slightly warmer
overnight lows will be found Sunday night - near 30 versus Sat
night`s low in the upper 20s.
The high lingers over the Appalachians through Tuesday as surface
flow shifts from the southwest to southerly early on. An upper
disturbance may bring some light rain Tuesday night and early
Wednesday, moreso near a developing warm front north of
Ohio/Indiana.
The southerly flow persists and remains generally light, leading to
a gradual yet persistent warming trend over the region. After the
coldest day starting the forecast period (still above normal),
readings will slowly warm to the upper 50s for highs on Wed/Thurs,
and mid 40s for overnight lows at the end of the forecast.
Thursday is showing the next probable chance for rain over the
region as a cold front behaving more like a windshift strings out sw-
ne along the Ohio River. As of now it would provide a focus for
increased moisture with good zonal southwest flow getting wrung out
somewhere in the Ohio Valley, potentially a good soaker of a rain.
Deterministic models are showing similar features with this system
but remain well too far out in time to do anything other than
increase the pops for this period and speak to it in this
discussion.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
While VFR conditions will begin the TAF period, conditions will
deteriorate significantly through the overnight. Ceilings are
expected to lower as the night progresses, ending up with
IFR/LIFR ceilings at all TAF sites by morning. As this occurs,
visibilities will also drop. While MVFR visibilities are the
most likely scenario, some IFR visibilities are possible, and
even likely at KDAY. In fact, there is some potential for dense
fog to develop at KDAY. As this occurs, there will also be a
chance for some very light rain or drizzle, but the main impacts
will not be from any precipitation. Winds overnight will start
out southerly, shifting to the southeast by morning.
Tomorrow, while visibilities may improve some through the
morning, ceilings are expected to remain very low -- IFR to
LIFR. If there is going to be any slight improvement in
ceilings, it will be late in the afternoon, but currently it
appears that conditions will remain IFR through the entire TAF
period.
Chances for rain showers will also increase tomorrow afternoon,
though there is low confidence on specific timing or placement.
Thus, this will be handled with a VCSH in the TAFs.
Finally, winds will increase after the tail end of the TAF
period, and LLWS is likely. LLWS has been included in the
extended portion of the CVG TAF.
OUTLOOK...MVFR/IFR conditions will continue into Friday night
and Saturday morning, and MVFR conditions may continue well into
Saturday. LLWS is expected Friday night. Thunderstorms are
possible late Friday night through Saturday morning. Sustained
southerly winds of 20-25kts expected Friday night, with
sustained westerly winds of 20-25kts and gusts to 30-40kts
expected Saturday.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...KC
NEAR TERM...KC/Hatzos
SHORT TERM...KC
LONG TERM...Franks
AVIATION...Hatzos
Area Forecast Discussion
National Weather Service Lincoln IL
829 PM CST Thu Dec 9 2021
.SYNOPSIS...
Issued at 212 PM CST Thu Dec 9 2021
A strong storm system will move across the region Friday night.
Ahead of it, areas of fog are expected over central and southeast
Illinois, then an increasing threat of showers and scattered
thunderstorms Friday afternoon and evening. Some potential exists
for severe thunderstorms south of a Champaign to Taylorville line
Friday evening. As the storm departs, expect a very windy period
late Friday night into Saturday, with wind gusts exceeding 40 mph.
&&
.UPDATE...
Issued at 817 PM CST Thu Dec 9 2021
This evening, a number of sites are reporting calm winds as a col
area is spreading across the lower Illinois River Valley.
Meanwhile, satellite imagery shows thicker mid and high clouds
over northern MO and central/southern IA moving east into
Illinois. Cloud cover looks to be most prevalent along and north
of the I-72 corridor but should gradually lift from the south.
Clearing skies, light/calm winds, and high dew points in the lower
40s will set the stage for fog development overnight. Still have
some concerns a dense fog advisory may be needed overnight.
&&
.SHORT TERM...(This evening through Saturday)
ISSUED AT 212 PM CST Thu Dec 9 2021
Lots to discuss in this part of the forecast. The developing storm
system is starting to take shape over Colorado this afternoon, and
should intensify as an upper wave currently in California moves
across the 4-corners region. Model guidance is in good agreement
with the surface low tracking to near Milwaukee by Saturday
morning.
1) Fog potential: Concern has been increasing recently over the
potential for dense fog overnight near and east of I-55, southeast
of where the warm front will be setting up. Increasing surface
moisture will bring dew points into the 40s in this area with a
low level inversion noted on forecast soundings. High-res model
guidance brings dense fog as far northwest as the Illinois River,
but that area`s a little more uncertain. Have added areas of fog
into the forecast into this region tonight and Friday, and will
monitor closely over the next few hours for a potential dense fog
advisory.
2) Severe potential: Latest SPC Day2 outlook brought the slight
risk up to a Pana-Danville line with the enhanced risk edging into
our highway 50 counties in southeast Illinois. Warm front is
expected to lift north of the CWA late afternoon. In the warm
sector to the south, HREF 0-1km storm relative helicity reaches
the 200-400 m2/s2 range with CAPE`s 500-1000 J/kg depending on the
model. HRRR model is slower with focusing the 8-midnight time
frame for the best severe threat, with the ARW and NAM Nest
mainly after midnight. QLCS type environment is more favored with
wind damage and brief tornadoes possible.
3) Wind potential: Behind the storm system, wind gusts 40-45 mph
likely after midnight Friday night and continuing much of Saturday
morning. BUFKIT soundings suggest some potential for 50+ mph north
of I-74. A wind advisory may be needed as we get closer.
4) Temperatures: Passage of the warm front will result in some
non-diurnal temperature trends later Friday, with Friday high
temperatures occurring in the evening and Saturday`s highs not too
long after midnight.
.LONG TERM...(Sunday through Thursday)
ISSUED AT 212 PM CST Thu Dec 9 2021
Focus on the longer range remains with the unseasonably mild as we
get toward mid week. Temperatures of 15-30 degrees above normal
continue to be advertised by the GFS/European ensembles. Low
temperatures Wednesday and Thursday mornings are likely to be
well above the normal highs for mid December. Upper ridging
amplifies as a developing storm system emerges from the central
Rockies, bringing the peak of the warmup. The core of the storm
system should track northeast, with a trailing front bringing some
showers toward Wednesday night and Thursday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 506 PM CST Thu Dec 9 2021
Main concern is with expected low clouds and fog as a warm front
sets up over central Illinois overnight. High-res guidance
continues to focus on expansion after 06Z potentially as far west
as KPIA. Will lower ceilings to below 500 feet at all sites except
KPIA, but IFR conditions likely there as well on the edge of the
stratus deck. Visibility around 1/2 mile appears likely elsewhere
late tonight into Friday morning, until the front lifts north.
Most improvement in visibility will be in the period after 18Z,
though clouds expected to remain below 1,000 feet in the
afternoon.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Deubelbeiss
SYNOPSIS...Geelhart
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart
Area Forecast Discussion
National Weather Service North Platte NE
538 PM CST Thu Dec 9 2021
.SHORT TERM...(This evening through Friday night)
Issued at 408 PM CST Thu Dec 9 2021
The main forecast challenge through Friday night revolves around the
incoming winter storm. Upper level zonal flow over Nebraska will
transition to southwest through the night as the trough currently
centered over California will dig into the Great Basin and Four
Corners. The trough then bisects the forecast area late Friday and
take on a more neutral tilt. At the surface, a low pressure near the
Denver metro is starting to deepen as of this afternoon. Not much
movement is expected overnight, but it really picks up steam
tomorrow as it ventures onto the Plains and ultimately reaches the
Quad Cities IA/IL area tomorrow night. Other factors compounding
this system are a strong H3 jet with speeds 120kt+ that eventually
becomes coupled late tomorrow and a deepening H7 low that tracks
right across the Sandhills.
As of 21z, the beginning of the baroclinic leaf is noted on water
vapor imagery, stretching from the Pacific Coast up to the Laramie
Range. Radar echoes in western Nebraska are showing the enhanced mid-
level moisture and cloud deck. Expect this activity to eventually
become the main deformation band as H5-7 frontogenesis ramps up
tonight. Isentropic upglide is rather strong, most notable at 290K,
which roughly corresponds to H7-85. Surface and low level winds are
also transitioning to more easterly flow. In addition to enhanced
moisture advection, upslope winds will aid in some forcing/lift. In
response, steadily increased PoP after 00z across northwest Neb.
Most of Sheridan and W.Cherry should receive moderate snow by 03z,
and the band beginning to stretch east along the Hwy 20 corridor by
06z. Will need to monitor the development of this band as dry air
reigns supreme in the low levels currently, as shown by 20-30F
surface dew point depressions at KGRN, KVTN, KONL. It will take some
time for the column to fully saturate, especially for areas east of
the panhandle. Checked forecast soundings for potential freezing
drizzle at the onset, but found little evidence. Still cannot be
completely ruled out, especially for the eastern zones where low and
mid level saturation will occur tomorrow morning and a surface
inversion capable of trapping moisture.
Thinking the 06z-12z timeframe will be crucial for snow accumulation
for the western half of the Winter Storm Warning areas. Forecast
soundings suggest ample lift in the H5-7 layer, which directly
correlates to the majority of the DGZ. Some solutions also show the
classic isothermal layer developing, increasing time for aggregates
in the DGZ. Additionally, cross sections indicate some slight theta-
E folding and negative EPV values from KCDR to KVTN. Snow rates may
exceed 1"/hr at times, leading to quick accumulations. Cold air
advection later in the night will help increase SLR`s from around
8:1 up to 14:1. One caveat in this setup is the northward trend in
the latest model guidance. The highest confidence for significant
snowfall (6-10") is generally along and north of Hwy 20. After 12z
Friday, things get more tricky, especially relating to the
widening/weakening of the main deformation band, the formation of a
second band, dry air intrusion, and the extent of wrap-around
moisture. Used a blend mainly consisting of HREF, NAMnest, RAP to
capture a general picture of timing, location, and qpf. The bulk of
the heavy snow should shift into South Dakota after sunrise, but
enough forcing at H5-7 remains across Nebraska to support a
southward extent of light to moderate snow. Forecast soundings
suggest at least a six hour window of appreciable precip as far
south as I-80 with the peak accumulation occurring mid-morning
through early afternoon. The thermal profile is not as supportive of
dendrites or heavy rates compared to the far north, but impacts will
likely still be felt. Bouts of stronger lift and variations in the
H85-7 temp that increase the DGZ may lead to pockets of heavier snow
embedded in the main batch of light snow. The second primary
deformation band may brush far north central Neb, generally Holt and
Boyd Cos, mid to late afternoon as the system strengthens over the
Upper Midwest. Thinking the greatest wrap-around activity will
affect far northern and northwest Neb, which may also be enhanced by
orographic lift along the Pine Ridge. Some light snow showers may
linger into the late evening hours over north central Neb, but all
snow should be done by 06z Sat. All in all, confidence decreases in
snow amounts outside the Warning area as there will likely be a
steep/narrow gradient of 6"+ and 1-2" amounts. With that said, made
no change to current headlines.
.LONG TERM...(Saturday through Thursday)
Issued at 408 PM CST Thu Dec 9 2021
The long term pattern in the extended period will be characterized
by broad height rises over the middle part of the country through
the weekend as the Friday system exists the area, resulting in a
quasi-zonal flow aloft transitioning to southwesterly flow as the
next long wave trough develops off the CA coast. Weekend
temperatures are expected to rebound fairly quickly under large
scale subsidence and sunshine, except of course where snow cover
will ultimately exist. Temps likely to remain below average in the
north and closer to average in the south Saturday (low-mid 40s),
but returning to above average for this time of year by Sunday.
Strong ridging and subsequent downstream jet streak intensification,
followed by anticyclonic wave breaking in the northern Pacific will
teleconnect to a building ridge by Monday into Tuesday and the first
part of Wednesday in the Plains. Model ensemble clustering suggests
differences in timing of the very quick moving upper low from the 4
corners region Tuesday into Wednesday. A general track of the upper
low moving across the northern Plains looks favored for now which
would put much of western and north central NE in the warm sector of
this approaching storm system Wednesday. While some instability is
suggested for Wednesday the trend for significant moisture return is
uncertain to support widespread rain with embedded thunderstorms at
this time. Precip chances have been included and will be fine tuned
as guidance refines moisture availability. There is high confidence
in very strong winds for Wednesday, both in the warm sector and
behind the cold front. Wind gusts over 35 mph looks likely at this
point.
The anomalous ridging developing across the Plains in the
Tuesday/Wed time frame may support record or near record high
temps once again, though timing differences in ensemble solutions
yields only medium confidence in that. But well above average
temps for that period does look likely. The anomalously warm temps
and strong winds on may well provide a critical fire weather
period Tuesday afternoon, but especially Wednesday afternoon. As
forecasts become more refined those details will be updated as
well, but the pattern suggests some concern in that time frame.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 537 PM CST Thu Dec 9 2021
KVTN: Flight conditions will be deteriorating as snow starts to
move in from the southwest. Expect conditions will go below VFR
early this evening as vsbys and cigs lower, then reach IFR after
Midnight. Snow will be heavy at times but will wait for more
definitive radar trends to develop before introducing more
specific timing. May see precipitation lighten up for a period
before daybreak but that will fill back in. Wind increases and
blowing snow develops with poor flight conditions throug the
latterportion of the valid period.
KLBF: Main band of snowfall will become established to the north
of KLBF, leaving VFR conditions through daybreak. However
easterly flow will enhance with wind gusts over 25kt expected by
early tonight. Snow and lower cigs arrive after daybreak with a
period of IFR conditions mid morning into early afternoon. Winds
will shift to a northwesterly direction and become gusty Friday
afternoon as low pressure moves off to the east with gusts over
30kt at times.
&&
.FIRE WEATHER...
Issued at 408 PM CST Thu Dec 9 2021
Despite the strong system on Friday, a rapid recovery in
temperatures in the far southwest part of the state to some degree
Saturday, but especially Sunday will still yield relative humidity
values dipping below 20 percent again in the far southwest part of
the state, assuming little to no snow cover. Winds for Saturday and
Sunday should remain below 20 mph for the most part however which
should lessen critical fire weather conditions.
As referenced in the long term section, anomalously warm temps and
strong winds on may well provide a more critical fire weather period
Tuesday afternoon, but especially Wednesday afternoon. As forecasts
become more refined those details will be updated as well, but the
pattern suggests some concern in that time frame. While relative
humidity forecasts are more uncertain at this time, there is decent
confidence in very strong winds especially Wednesday ahead of the
strong system, and a potential wind shift from west to northerly as
well later as the system passes.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 6 PM CST /5 PM MST/ Friday for NEZ004-
094.
Winter Weather Advisory until 6 PM CST /5 PM MST/ Friday for
NEZ022>024-035-036.
Winter Storm Warning from midnight CST /11 PM MST/ tonight to 6
PM CST /5 PM MST/ Friday for NEZ005>010.
Winter Weather Advisory from midnight tonight to 6 PM CST Friday
for NEZ025>029-037.
&&
$$
SHORT TERM...Snively
LONG TERM...Stoppkotte
AVIATION...MBS
FIRE WEATHER...Stoppkotte
Area Forecast Discussion
National Weather Service Marquette MI
652 PM EST Thu Dec 9 2021
.SHORT TERM...(This evening through Friday)
Issued at 401 PM EST THU DEC 9 2021
Water vapor imagery and RAP analysis show a southern stream
shortwave lifting into the Upper Great Lakes this afternoon, and as
expected, forcing from this wave is causing a flare up of system
snow, especially into central Upper Mi. The forcing from this wave
will also provide lake enhancement of snow into the se portion of
the cwa and over the tip of the Keweenaw in a se flow. I issued a
winter wx advisory earlier this afternoon for Delta/southern
Schoolcraft and advisories still continue for Ontonagon thru
Keweenaw counties thru 00z this evening. Expect additional snow
amounts of 1 to 2 inches through early evening for the advisory
areas. Could maybe see isolated amounts of 3 inches in
Delta/southern Schoolcraft with the added boost from lake
enhancement.
A second northern stream shortwave moving from Manitoba into Ontario
will push the sfc trough east across the fcst area this evening as
winds shift from southerly to southwest or westerly behind it. At
the same time, snow will be tapering off from west to east this
evening. Expect fairly quiet and dry weather late tonight into much
of Friday as high pressure builds in from the west. Some light snow
ahead of a more significant storm system approaching from the CO
Rockies could spread into south central zones late Friday.
Min temps tonight will range from the mid to upper teens interior
west to the 20s elsewhere. Highs Friday will be in the lower to mid
30s.
.LONG TERM...(Friday night through Thursday)
Issued at 355 PM EST THU DEC 9 2021
Main attention in the extended period is the potential for a winter
storm Friday night into Saturday. Shortwave currently making its way
into Nevada will continue eastward tonight. Its progged to exit the
Rockies and then lift northeast toward the Upper Great Lakes
tomorrow. By 0z Saturday, guidance suggests its surface low will be
near the Iowa/Missouri stateline. There are some differences among
the 12z guidance as to how deep the system will be initially, but
the consensus among the guidance suite is that the system will
continue deepening as it continues to interact with favorable upper
level jet dynamics while entering the Upper Great Lakes. From there,
the feature will begin taking on a negative tilt just downstream
late Saturday as it enters Ontario.
As the system lifts toward the region, strong isentropic and low-mid
level fgen forcing ahead of the system will support snow showers
spreading over the forecast area by Friday evening. With the strong
low level q-vector signal and the deepening moisture, expecting
snowfall to become moderate to heavy across mainly the central and
eastern UP during the evening and through the night. As the low
approaches, the flow will become northeast which will bring an
opportunity for lake enhancement for areas along the Lake Superior
lakeshore. This flow pattern and an added terrain boost will also
help Lake Superior lakeshore communities see some of these higher
snow amounts, particularly across Marquette and Alger counties. 6z
GFS suggested enough WAA on the system`s eastern flank could be
enough to support a ptype change over to rain or freezing rain late
Friday night/Saturday morning along the Bay/Lake Michigan lakeshores
and east. The 12z guidance continues to suggest this potential, and
even the Canadian is suggesting a switch to rain by the end of the
event in the east. 9z SREF Plumes also suggest the potential for
mixed ptype. Outside of the likely snow though, this ensemble system
suggests a switch over to rain would be more likely then freezing
rain, albeit this probability still remains low (~20 percent or so).
This appears consistent with the NBM v4.1 as well.
If this does occur, icing accumulations look light, but could be
something to watch as new guidance arrives. At the moment, snow
totals look to vary between 8 and 12 inches across the central and
east, with some potential above a foot in the higher terrain just
west and south of Marquette. The west looks to be largely spared
from a majority of the snow given the tightly wrapped nature of the
comma structure that`s expected to move over the region, but 3 to 5
inches of snow still looks possible. Opted to upgrade the watch to
Winter Storm Warnings and Winter Weather Advisories for the event.
The system will pull away Saturday, with CAA and a tight pressure
gradient to follow. This will result in strong winds and areas of
blowing snow. Because the snow is expected to be wetter and heavy,
not only will driving conditions be hazardous and snow removal
require more effort, but power outages can`t be ruled out.
After this system lifts out, the jet stream is progged to retreat
north. This will be accompanied by ridging extending over much of
central CONUS and near zonal flow over our region Sunday through at
least Wednesday. GEFS 500mb height spaghetti plot shows good
agreement among its various members, so confidence is high that the
expected warming period is still on track. The beginning of next
week looks to start off with highs near 40F and then by mid-week,
potentially some mid 40s. Snow melting should be slow to occur given
overnight lows dropping below freezing across the board, low sun
angle, and daytime dewpoints not much above freezing, except perhaps
Wednesday.
Beyond this there are differences among the guidance. At the moment,
there is the potential for another notable system Wednesday night
or Thursday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 643 PM EST THU DEC 9 2021
As a system pulls away to the east tonight, conditions will improve
at all terminals from west to east. Conditions have already improved
to MVFR at CMX and IWD and should return to VFR by Friday morning.
IFR conditions at SAW will improve to MVFR in a couple hours and
then to VFR Friday morning. Another system will move across Upper
Michigan Friday night through Saturday morning, likely bringing IFR
to LIFR conditions at all terminals.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 401 PM EST THU DEC 9 2021
Ahead of an approaching surface trough, southerly winds have
increased today. Into early evening, southerly winds of 20-30kt with
maybe a few gale force gusts to 35kt will continue west with gales
to 40 kts central and east. As the trough passes tonight expect w to
nw winds to 20-30kt for a time in its wake. A weak high pres ridge
reaches Lake Superior by late Fri aftn, providing a period of light
winds under 15kt. Deepening low pres will then track ne, passing
near the Straits of Mackinac Sat morning. N to NW gales of 40kt will
likely occur across the e half of Lake Superior on Sat as the
deepening low continues lifting ne. Would not be surprised to see
even a few high-end gale gusts to 45 kts. W to sw winds of 20-30kt
are then expected Sat night into Sun as another low tracks e toward
northern Ontario. Could be a few gale force gusts across western and
north central Lake Superior on Sun. As a sfc high pressure ridge
builds over the lake, expect winds to generally be 20 kts or less
by Mon afternoon into Tuesday.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Storm Warning from 7 PM EST /6 PM CST/ Friday to 10 AM
EST /9 AM CST/ Saturday for MIZ002-009-084.
Winter Storm Warning from 7 PM Friday to 4 PM EST Saturday for
MIZ006-007-013-014-085.
Winter Weather Advisory until 7 PM EST this evening for
MIZ001>003-013-014.
Winter Weather Advisory from 9 PM Friday to 10 AM EST Saturday
for MIZ001-003.
Winter Storm Warning from 7 PM EST /6 PM CST/ Friday to 1 PM EST
/noon CST/ Saturday for MIZ004-005-010>012.
Lake Superior...
Gale Watch from Saturday morning through Saturday evening for
LSZ251-267.
Gale Warning until 7 PM EST this evening for LSZ244-245-249>251-
264>267.
Gale Watch from Saturday morning through Saturday afternoon for
LSZ249-250-266.
Lake Michigan...
Gale Watch from Saturday morning through Saturday afternoon for
LMZ221-248-250.
&&
$$
SHORT TERM...Voss
LONG TERM...JP
AVIATION...JAW
MARINE...Voss
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
810 PM MST Thu Dec 9 2021
.UPDATE...
Issued at 810 PM MST Thu Dec 9 2021
Current surface analysis shows cold front well south of the region
now, with an area of low pressure developing along it across eastern
CO. High pressure is centered over north central SD. Upper level
analysis shows near zonal flow across much of the region, with a
potent shortwave now over ID and western UT. Strong jet and
increasing upper level moisture to the east of the wave is moving
east-northeast across the central Rockies and into the high Plains.
Skies have clouded over across much of the area, with the lower
clouds over southern portions of the region. Drier air to the north
and northeast of the Black Hills is holding strong on the back side
of the surface high. The burst of snow that developed across the
central and southern Black Hills this afternoon has tapered off
some, with mostly areas of light snow and flurries across southwest
SD at this time. Regional radars show the heavier snow developing
across southeast WY into the NE panhandle over the last couple of
hours, and will start to move into southern parts of northeast WY
and southwest SD over the next few hours.
Forecast still looks to be on track for the most part through
tonight and into Friday morning. The heaviest snow will fall
overnight and into Friday morning across the warning areas, with 6
to around 12 inches, highest amounts generally toward the NE border
in southwest SD. Amounts will taper off pretty sharply toward the
Interstate 90 corridor and especially over extreme northeast WY and
northwest SD. The only change to the headlines was to put the
central Black Hills in a warning, with some areas along the
eastern slopes from Hill City and Pactola to Keystone and
Rockerville likely seeing around 6 inches of additional snow on
top of the 1 to 3 inches from this afternoon. Otherwise, only
minor adjustments made to the forecast for tonight at this point.
&&
.DISCUSSION...(This Evening Through Thursday)
Issued at 115 PM MST Thu Dec 9 2021
Most recent upper air analysis shows the long-wave trough situated
over the rockies, with the low poised over Colorado moving east
northeast that will support frontogenesis this evening into
Friday morning. Latest HRRR and SREF runs show potential for weak
development over the Black Hills this afternoon, but more
widespread snow will move into the area as the wave moves into the
CWA later this evening. Deterministic models all agree on broad
FGEN band along the SD/NE border creating the highest amounts
(6"+) over the forecast area. Snowfall amounts drop off further to
the north, especially north of I-90, with 850mb models showing
much drier air the northern half of SD. Snow will taper off from
west to east Friday morning and afternoon. Have kept with the
trend of lowering temperatures for Friday night, in areas where
snow pack is expected. Looking ahead through the weekend and into
next week, upper ridging moves into the western CONUS and brings a
warming trend, with temperatures reaching back into the 50s and
possibly 60s Mon-Weds. Models hint at another strong low pressure
system moving into the upper plains middle of next week, and we
may see another drop in temperatures, along with strong winds and
snowfall potential.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 437 PM MST Thu Dec 9 2021
Snow and MVFR/IFR conditions will gradually spread east-northeast
across much of northeast WY, the Black Hills area, and southwest
SD through the evening hours, and eventually into south central SD
overnight. VFR conditions are expected across much of northwest
SD tonight into Friday, especially the far northwest. Snow will
taper off and conditions will gradually improve from west to east
across northeast WY and southwest SD on Friday. The heaviest snow
and worst conditions will be across far southern SD overnight into
Friday morning.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 11 AM MST Friday for SDZ024-026-
031-072.
Winter Storm Warning until 2 PM MST Friday for SDZ027>030-
041>044-074.
Winter Storm Warning from midnight tonight to 6 PM CST Friday
for SDZ046-047-049.
WY...Winter Weather Advisory until 11 AM MST Friday for WYZ055-057-
058.
&&
$$
Update...26
DISCUSSION...Dye
AVIATION...26