Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/15/22
Area Forecast Discussion
National Weather Service Boston/Norton MA
1011 PM EST Wed Dec 14 2022
.SYNOPSIS...
Quebec high pressure yields dry weather and easing winds tonight,
with moderating temperatures Thursday. Low pressure then tracks
along or near the southern New England coast Thu night and Fri,
delivering a chilly windswept rain, except heavy wet snow is
likely across the high terrain of western Massachusetts. Behind
this departing low, a drying and cooling trend this weekend,
along with blustery west to northwest winds. Dry weather likely
lingers into early next, but likely with colder than normal
conditions.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
10 PM Update...
Increased precipitation chances toward the latest NAMNest/NSSL
WRF guidance based on current observations of the shower
activity pushing in. Should see this activity diminishing by
roughly 05-07Z as it moves in. Rest of the forecast is on track.
Previous discussion...
Minor tweaks to the ongoing forecast this evening. Last couple
of runs of the HRRR and RAP were more potent with an offshore
band of showers set to move across the eastern MA coastal waters
into portions of eastern MA later this evening. Latest regional
radars also showed this band holding together pretty well,
despite likely overshooting the echoes to some degree. The
greatest risk for mostly rain showers should be across the
coastal waters, and towards the outer Cape and Nantucket.
Also brought temperatures and winds back in line with observed
trends. Gusty winds were diminishing a little bit faster.
Previous Discussion...
Gusty winds continue late this afternoon and evening as the
surface low offshore makes its closest pass between 4 and 7 pm.
This tightens the pressure gradient further and a 45kt+ jet
moves over the extreme eastern coast. Thus, for areas along
the coast like Cape Cod and the islands wind gusts will hold
steady or even slightly surge early this evening. Further
inland, after sundown surface temps drop and winds will cease to
mix down so should see a more rapid decrease of winds inland.
Tonight our blocking pattern begins to breakdown as the mid
level ridge approaches, as does high pressure at the surface
(leading to the end of gusty winds by sunup). On its way out,
though, a final shortwave rotates around the upper low and
brushes eastern southern New England. This, along with surface
winds veering to the northeast, will generate scattered ocean
effect rain showers over Cape Cod and potentially extending into
eastern Massachusetts as ocean effect snow showers; the window
for these rain and snow showers would generally be between 8pm
and midnight, give or take a few hours.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday the trough-ridge-trough pattern continues its march
eastward, sliding the ridge axis across southern New England by
mid afternoon. This makes for a quiet and mostly dry day, with
light winds much of the day. The only exception to the dry
forecast may be for some scattered ocean effect rain showers
thanks to the northeasterly flow around the high. Best chance
for this precip will be over eastern MA and RI, with lesser
chance further west in MA and CT. So, even though the warm
frontal high clouds ahead of the approaching storm system will
only just be arriving by sunrise, surface northeast winds will
keep low level clouds around all day. Clouds thicken and lower
through the day and into the evening ahead of the approaching
system, while temperatures moderate a bit, especially for
eastern MA and coastal RI thanks to northeast flow off the
ocean, which is still in the 40s and low 50s. Highs here reach
into the low 40s.
While moisture (and cloudcover) increases on Thursday, the
appreciable precipitation (rain and snow, not counting the
previously mentioned ocean effect showers) should hold off until
Thursday evening as it will take some time to overcome mid level
dry air. The instigator of this is a low pressure that forms
over the mid Atlantic along the triple point of a parent low
over the Great Lakes. This low track up the northeast coast and
then over southern New England. Most guidance (with the
exception of the GFS) is honed in on a track over Cape Cod which
produces a cold rain scenario for much of the region, with heavy
heavy, wet snow over the higher terrain thanks to the moderate
antecedent temperatures. There is ample moisture to work with
given PWATs 1-2 standard deviations above normal, but again the
fly in the ointment will be marginal temperatures thanks to the
low level easterly flow. Warm advection aloft will initiate rain
and snow by 00Z Thursday, quickly overspreading the region. A
warm nose moves north rather quickly, so even some inland
locations that start off as snow should change to snow rather
quickly. For locations above 1,000 ft though, warmer air is
expected to be overcome by the strong easterly, upslope flow
which should induce some dynamic cooling. Easterly winds at 850
mb will be blowing at 40-45 kts. As we`re just getting into some
of the high-resolution guidance, confidence in snow amounts by
sunrise Friday is rather low. Advisory level snows (3 to 7
inches in the Berkshires) are all but certain by 7 am (90%
probability in the EPS, 70% in the GEFS), with less certainty of
seeing warning criteria (7 inches or greater) by sunrise. The
struggle with this system will be a tight snowfall gradient
given the elevation dependent nature of it.
A Winter Storm Watch has been issued accordingly for the slopes
of the Berkshires as well as Hartford county, though only the
extreme northwest portion of Hartford county is expected to see
impacts from this system.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Highlights
* A windswept rain Friday, with heavy wet snow possible high
terrain of western MA/CT
* Dry but trending colder & blustery this weekend into early next
week
Precipitation...
Complex forecast for Friday into Saturday, with some lingering
uncertainty in the details. Temperatures in the lowest levels of
the atmosphere will marginally support snow, especially during
the daytime hours. Thus, accumulation snowfall across southern
New England will be very elevation-dependent. Expecting a sharp
gradient between where the snowfall accumulates significantly,
versus those that are mainly rain. A small change in temperature
could lead to a large change in snowfall. Will need to monitor
temperatures closely through this event.
At present, confined significant snowfall accumulations at
elevations at or above 1,000 ft. The consistency of the snowfall
for most should be heavy and wet, trending to a drier snowfall
at the highest elevations of southern New England. This may
change with later forecasts, so stay tuned.
Otherwise, expecting a significant precipitation event to begin
winding down from west to east during the day Friday, and
especially Friday night. Thinking there could be a brief final
burst of snow across the higher elevations when the colder air
surges south.
Strong East Winds...
Frontal wave is associated with a 65 kt low level easterly jet.
Model soundings suggest east winds may gusts up to 40-50 mph along
the coast. Wind Advisories may be needed for portions of the
coast, especially Cape Cod and the islands.
Coastal Flooding...astronomical tides are very low, and will
likely preclude any inundation or erosion issues.
Weekend and Early Next Week...
Frontal wave exits northeast Saturday, with a dry slot
overspreading our region. Thus, drying trend begins Saturday.
Mainly dry Sunday, but can`t rule out a few flurries or snow
showers, as shortwave trough moves across the area. Behind this
trough, mainly dry with temperatures trending near or below
normal, along with blustery west winds.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent. High -
greater than 60 percent.
Tonight...High confidence.
VFR with NW winds becoming N/NNE and diminishing. Expect winds
to diminish to 5-15 kts by 06Z with gusts of 15-25 kts. Still
could have some spotty showers across the Cape/ACK later this
evening.
Thursday...High confidence in trends, moderate in exact timing.
VFR to start, cigs lowering to MVFR/IFR during the afternoon as
winds become more NE. Could see some precipitation spreading in
during the afternoon. Looks to be mainly snow across the
interior and rain for the coastal plain. Winds 5-15 kts with
gusts of 15-20 kts.
Thursday night...Moderate confidence.
MVFR becoming IFR as rand and high elevation snow showers
overspread the region. East winds become increasingly gusty
through the overnight hours, eventually blowing 10 to 15 kt with
gusts to 25 kt.
KBOS Terminal...High confidence.
KBDL Terminal...High confidence.
Outlook /Friday through Monday/...
Saturday: MVFR/IFR conditions possible. Windy with local gusts
up to 30 kt. Chance RA, chance SN, slight chance FZRA.
Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SN.
Sunday through Monday Night: VFR. Breezy.
Tuesday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
10 PM Update...
Have converted the rest of the Gale Warnings to Small Craft
Advisories in the latest update. Forecast remains on track
otherwise.
Previous discussion...
Winds were diminishing a little faster than previously expected.
Converted some of the Gale Warnings to Small Craft Advisories.
Expecting that remaining Gale Warnings will be able to be
converted later this evening. Small Craft Advisory conditions
likely to persist across the eastern coastal water through
Thursday.
Tonight...High confidence.
Winds N at 15-30 kt to start, decreasing to 15-20 kt by
midnight and shifting to the NNE. Gusts of 20-30 kts after
midnight. Seas diminish to 6-8 ft for the outer waters after
midnight and 3-6 ft for the inner.
Thursday...High confidence.
Winds out of the NNE to NE at 10-20 kts with gusts of 15-25 kts.
Seas 7-9 ft for the eastern outer waters and 3-7 ft across the
interior waters. Light rain showers may spread in late in the
afternoon.
Thursday night...High confidence.
SHRA. E winds increase to Small Craft Advisory criteria early
in the evening, up to 30-34 kt by 12Z. Seas 7-10 ft.
Outlook /Friday through Monday/...
Saturday: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Rough seas up to 14 ft. Chance of
rain.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft. Slight chance of
rain.
Sunday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain showers.
Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft.
Monday through Monday Night: Moderate risk for Small Craft
Advisory winds with gusts up to 25 kt. Areas of rough seas.
Tuesday: Winds less than 25 kt. Seas up to 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Watch from Thursday afternoon through Saturday
morning for CTZ002.
MA...Winter Storm Watch from Thursday afternoon through Saturday
morning for MAZ002-008-009.
RI...None.
MARINE...Small Craft Advisory until 1 AM EST Thursday for ANZ230-
235>237.
Small Craft Advisory until 7 PM EST Thursday for ANZ231-232-
251.
Small Craft Advisory until 7 AM EST Thursday for ANZ233-234.
Small Craft Advisory until 1 AM EST Friday for ANZ250-254-255.
Small Craft Advisory until 10 AM EST Thursday for ANZ256.
&&
$$
SYNOPSIS...Belk/BL/BW
NEAR TERM...Belk/BL/BW
SHORT TERM...BW
LONG TERM...KJC
AVIATION...Belk/BW
MARINE...Belk/BW/BL
Area Forecast Discussion
National Weather Service Cheyenne WY
751 PM MST Wed Dec 14 2022
.UPDATE...
Issued at 751 PM MST Wed Dec 14 2022
Quick update for winter/high wind headlines and expiration times.
The Blizzard Warnings were extended until late Thursday afternoon
for the Northern NE Panhandle for the continuation of strong winds
and blowing/drifting snow. The Blizzard Warnings for the Southern
Panhandle, East Laramie County and South Laramie Range were downgraded
to Winter Weather Advisories, all expiring at 5 PM Thursday. No changes
were made to the High Wind Warnings (East Platte/South Laramie Range
Foothills/Central Laramie County), Winter Storm Warnings (Snowy/Sierra
Madre) and Winter Weather Advisory (Arlington/Elk Mountain), which
expire at 11 PM this evening.
&&
.SHORT TERM...(This evening through Friday)
Issued at 330 PM MST Wed Dec 14 2022
Lingering impacts from the recent major winter storm will remain
the main forecast concern for the next several days. Strong winds,
blowing snow, and cold temperatures will be here to stay through
the rest of the work week.
The large low pressure system dominating the weather over the
CONUS this week continues to slowly meander northeastward. The
surface cyclone has gradually weakened over the last 24 hours or
so, now analyzed at just under 1000-mb. The low is now vertically
stacked and will continue to slowly weaken and move northeastward
under weak steering flow. The cloud structure per GOES satellite
imagery has become broader but more ragged over the last 24 hours,
but some cloudier areas can be seen rotating around the low`s
western flank moving from north to south across our area. This is
producing lingering snow showers. While the snow is much less
widespread than yesterday, some localized areas are seeing
snowfall just as intense for brief period. For example, a few
hours ago a band of heavy snow developed just outside of the
continuing blizzard warning in central Laramie county, which
prompted a short fuse snow squall warning. This area is concurrent
with significant RAP analyzed 700-mb frontogenesis that extends
across the very southeast corner of WY. It appears that subsidence
associated with the strong winds over the southern Laramie range
is winning out over the Cheyenne metro, keeping the focus for
continued snow showers just to the north and east. RAP guidance
shows this frontogenesis subsiding over the next 3 hours or so,
which should weaken this lingering snow shower activity as
subsidence expands further east across the I-80 corridor. On the
synoptic scale, weak ridging will push into the Pacific Northwest
over the next 1-2 days. The downstream edge of the ridge will
support a moderately strong surface high developing over
Idaho/Montana/western Wyoming. The encroaching ridge and building
surface high will keep low-level height gradients and surface
pressure gradients quite strong over the next few days even as the
cyclone weakens. This will keep the wind machine blowing strong
for the next 48 hours or so.
The main source of uncertainty in the short term forecast is how
long the snow will continue to blow around for. Webcams, spotters,
and visibility sensors have indicated that blizzard conditions
have likely come to an end for much of east central Wyoming with
visibility improving to over one quarter mile. Thus, decided to
cancel the blizzard warning for these zones (101, 102, 107, 108).
The strong winds and potential for lee-side enhancement prompted
us to expand the High Wind Warning northward into zone 107, and
messaged blowing snow impacts in this warning. Elsewhere, the
winds should remain under High Wind criteria, so opted for a
Winter Weather Advisory to cover the blowing snow impacts for the
other zones. In addition, high res models continue to show light
snow lingering in southern Niobrara county around Lusk, with
another 1-3" possible in some areas. In the Nebraska panhandle and
eastern Laramie county WY, there is more snow on the ground to
blow, and spotters/webcams have indicated near-blizzard conditions
continuing in some areas. Thus, will let the blizzard warning
continue, but later shifts will have to decide whether or not to
extend into Thursday.
Even if blizzard criteria is not reached tomorrow, impactful
blowing snow is likely across the Nebraska panhandle. Strong winds
will refuse to relent as 700-mb winds of 45 to 60 knots cover most
of the area east of the Laramie range through midday Friday.
Bumped up the gridded wind forecast in the Nebraska panhandle
closer to the NBM 90th percentile with this update to account for
this. The cross Laramie range MSLP gradients look to drop off
slightly which may reduce winds in the I-80 summit area. In-house
models have caught onto this and show low odds for high winds
after 12z Thursday, but ramp up probabilities early Friday as
cross-barrier MSLP gradients creep up again. Winds could be close
to High Wind criteria across the area, but don`t have the
confidence for any watches/warnings at this time, especially since
several zones struggled to hit that today. There is high
confidence in continued wind gusts in the 45 to 55 MPH range, but
lower confidence in getting gusts higher than that. That should be
plenty to continue to produce blowing snow, but confidence in this
reaching ground blizzard criteria is low. We will take this one
day at a time going forward, evaluating how the snow is blowing
each day. The main takeaway is that impactful blowing snow and
strong winds are likely to continue through both Thursday and
Friday.
Lastly, we are also watching another weak shortwave that will
complicate the forecast west of the Laramie range for the next 36
hours. Clouds associated with this vort-max are already visible
over the northern Rockies. Expecting this system to start
enhancing snow shower activity over Carbon and Albany counties
late tonight, continuing through Thursday. A few light snow
showers could linger in the mountains through Friday, but overall
activity should be winding down by Thursday evening. Accumulations
will be light, around a dusting to 2" for the lower elevations,
and perhaps 1 to 4" in the mountains with localized 6" on the
higher peaks possible.
.LONG TERM...(Friday night through Wednesday)
Issued at 330 PM MST Wed Dec 14 2022
A cool & blustery forecast period ahead w/ strong quasi-zonal flow
aloft remaining intact across the northern CONUS. Elevated 700/850
mb CAG-CPR gradients between 50 and 70 meters, coupled w/ a narrow
ribbon of 45-50 knot flow in the H7-H8 layer should support a risk
for 60+ MPH wind gusts at Arlington/Bordeaux from Saturday through
early Sunday. Medium-range models remain in general agreement with
a significant cold snap possibly arriving as early as Wednesday as
a 1050+ mb arctic high infiltrates the central US. It remains just
a bit uncertain regarding the overall degree of the cold air mass,
as it may relate to daytime highs and overnight lows. However, our
confidence is very high for temperatures well below seasonal norms
by mid-to-late week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 454 PM MST Wed Dec 14 2022
Strong northwest winds continue across much of the area with light
snow showers over the Nebraska Panhandle. These strong winds have
led to reductions to visibility with blowing snow and will continue
this evening. Additionally, strong winds will continue into Thursday
afternoon leading to blowing snow once again, while snow showers
will linger around KCDR and KAIA. This will most likely result in
MVFR conditions for area terminals, especially in the Nebraska
Panhandle. Overnight snow showers will also be possible near KRWL
resulting in reduced flight conditions.
&&
.FIRE WEATHER...
Issued at 141 AM MST Wed Dec 14 2022
Departing winter storm has covered much of the region with snow.
With temperatures expected to be well below freezing, existing
snowpack will stick around for several days, keeping fire weather
concerns low. Gusty winds across much of SE Wyoming and the
Nebraska Panhandle will continue into the weekend.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 5 PM MST Thursday for WYZ101-102-
108-116-119.
High Wind Warning until 11 PM MST this evening for WYZ107-117-
118.
Winter Weather Advisory until 11 PM MST this evening for WYZ110.
Winter Storm Warning until 11 PM MST this evening for WYZ112-114.
NE...Blizzard Warning until 5 PM MST Thursday for NEZ002-003-095-096.
Winter Weather Advisory until 5 PM MST Thursday for NEZ019>021-
054-055.
&&
$$
UPDATE...MAJ
SHORT TERM...MN
LONG TERM...CLH
AVIATION...MB
FIRE WEATHER...AW
Area Forecast Discussion
National Weather Service Quad Cities IA IL
904 PM CST Wed Dec 14 2022
.UPDATE...
Issued at 850 PM CST Wed Dec 14 2022
Updated the forecast for the overnight period with slightly
colder surface and wet-bulb temperatures, which results in a
quicker changeover from rain to snow. This is a dynamic system and
latest model guidance is in good agreement on the quick switch to
snow between 11 PM and 1 AM.
For snow accumulations, there is a wide range in potential
outcomes due to marginal temperatures. On the low end the far
north receives under 1", but on the higher end locations north of
highway 30 and along/east of the Mississippi River could pick up a
quick 2-3 inches of heavy wet snow. Lower amounts are anticipated
down toward the I-80 corridor.
Impressive upper jet exit divergence, PVA with strong curvature
in the mid-level flow, and renewed low to mid-level theta-e
advection will produce moderate to strong ascent across the area
overnight, leading to widespread precipitation and top-down
cooling in the column toward 32 F or colder. Anticipate a 1 - 3
hr window of moderate to heavy snowfall in central and eastern
sections along/north of I-80. Accumulation efficiency will be
limited by the warm ground and SLRs likely in the 6:1 to 9:1
range. For these reasons, held off on a winter weather headline
and instead will message reduced visibility and brief slippery
travel impacts with Special Weather Statements and weather story
graphics.
&&
.SYNOPSIS...
Issued at 235 PM CST Wed Dec 14 2022
A closed upper level low is visible on water vapor imagery over
eastern South Dakota. A narrow dry slow is visible on satellite in
east central Iowa. At the surface, low pressure sits in northeast
South Dakota with an occluded front arching from the surface low to
KALO to near KCID/KIOW with a triple point in the vicinity with a
warm front near Interstate 80 and a cold front extending southward.
Precipitation was just east of the forecast area across Illinois.
There are low clouds and mist across the area north of the warm
front and east of the occluded front. There also continues to be
patchy dense fog across the area. Temperatures are warm and ranged
from 43 degrees at Dubuque, Freeport and fairfield to 55 degrees at
Moline.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 235 PM CST Wed Dec 14 2022
Key Messages:
1. Turning colder tonight into Thursday.
2. Low confidence in precipitation type and accumulation tonight.
3. Snow showers and breezy on Thursday.
Discussion:
The main forecast concerns were where the back edge of the
precipitation will setup tonight and if there will be any
accumulating snow overnight.
The vertically stacked closed low will move from eastern South
Dakota into western Iowa/Minnesota by 12 UTC on Thursday. The
surface low will have moved into north central Iowa with the its
associated fronts north and east of the area. Behind the front, cold
advection will result in low temperatures around 30 degrees on
Thursday morning. Vorticity rotating around the upper level low
tonight will lift along the frontal boundary and spread
precipitation across the area from east to west. The latest model
runs show the back edge of precipitation along and east of a
Manchester to Burlington Iowa line. Precipitation will likely begin
as all rain and begin to transition to all snow after tonight as
colder air moves into the area. The NAM delays the colder air moving
into the region to after 09 UTC while the GFS and CAMS bring it into
the area around midnight. This will result in a wintry mix at first
along the western edge of the precipitation. The warm ground
currently in place across the area will limit accumulation. There is
currently no snow accumulation in the grids but the GFS and HRRR
models are showing 1 to 3 inches of snow along the Highway 20
corridor due to the faster arrival of colder air. This overall
results in a lower confidence in the forecast.
The nearly vertically stacked system will wobble northeastward
through the day on Thursday and move into northeast Iowa and
southeast Minnesota. Expecting snow showers to develop across the
area with several disturbances rotating around the upper level low
providing enough lift to produce light snow across the area. High
temperatures through the day will be in the mid 30s. Accumulations
of a half an inch of snow or less are possible Thursday afternoon.
Additionally, west to southwesterly winds will strengthen on Thursday
as the gradient strengthens
.LONG TERM...(Thursday night through Wednesday)
Issued at 235 PM CST Wed Dec 14 2022
Key Messages:
An upper low will keep our weather unsettled and cool through
Friday, with occasional light snow/ snow showers.
Colder weather remains forecast in the week ahead, potentially
dealing with Arctic air.
The upper low is forecast to remain near our area, largely
positioned over Wisconsin, through Friday night. Our area is
consistently forecast to be within the closed cyclonic flow aloft,
and in a seasonally cool air mass. This will provide numerous rounds
of lift, and enough saturation for periods of light snow, especially
in the north 1/2 of the area. While accumulations each period are
generally an inch or less, we should see at least a decent chance
for whitening the ground, allowing for the upcoming air mass this
next week to drop our temperatures below 10, if not below zero in
areas that have snow cover (north 1/2).
Once the upper low moves east of the region by Saturday, dry weather
is generally forecast, despite the cold air arriving early next
week. Highs in the 20s, with lows in the single digits and teens are
forecast through Tuesday. Again, if we have snow cover at that time,
we could be below zero for lows. By mid week, models suggest another
system may move through the midwest ahead of another surge of Arctic
air.
ERVIN
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 545 PM CST Wed Dec 14 2022
Conditions will deteriorate tonight as widespread rain moves in
from the southeast. There will be a sharp cutoff on the southwest
edge of the precipitation which will set up near or just east of KCID.
A changeover to all snow is anticipated at DBQ and possibly MLI,
which could be heavy for several hours. Thus expect ceilings and
visibilities to drop to IFR/LIFR and there is potential for slushy
accumulation on pavement at DBQ where snow rates could reach
0.5"+ per hour. Moderate snow is possible at MLI for a few hours
late tonight; however, confidence is low this far south.
Wrap around snow showers and gusty SW winds are expected on
Thursday with ceilings between 1000-2000 ft AGL through the day.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
UPDATE...Uttech
SYNOPSIS...Cousins
SHORT TERM...Cousins
LONG TERM...Ervin
AVIATION...Uttech
Area Forecast Discussion
National Weather Service Flagstaff AZ
846 PM MST Wed Dec 14 2022
.SYNOPSIS...Dry weather with cold temperatures is expected through
Friday. Temperatures gradually begin to rise over the weekend and
into early next week.
&&
.UPDATE...Clear skies and light winds will result in prime
radiational cooling overnight tonight. This combined with still a
decent snow pack will result in another cold night is in store
for much of Arizona, with much of the High Country expected to be
in the single digits.
The only notable exception to this appears to be downwind of the
San Francisco Peaks especially near Agassiz Peak/Snowbowl. Very
fine-scale effects have resulted in temperatures rising to around
20 degrees F with a strong north-northeasterly wind gusting to
around 40 to 50 mph. Hi-res guidance from the HRRR looks to
continue these gusty winds through the night, then diminishing
through the morning.
Minor updates this evening to adjust temperatures and winds
overnight. Otherwise, the afternoon package remains unchanged.
Previous discussion continues below.
&&
.PREV DISCUSSION /200 PM MST/...Our current cold spell is one
result of a persistent longwave trough over the western two-thirds
of the country. Ripples in this upper-level pattern will help
inject periods of mild breeziness over the coming days. On Friday,
northerly winds may gust 20-30 mph over the highest, most exposed
terrain. Periods of cloudiness are also possible this weekend. No
precipitation is forecast. There is a chance for patchy nighttime
fog each day through the weekend. Outside of below-average
temperatures, weather- related impacts over the next week will
remain minimal.
Expect a few more bitterly cold nights across northern Arizona.
Morning low temperatures will broadly dip into the single digits
for the high country until next week. Below zero temperatures are
likely in environmentally vulnerable areas. These vulnerable areas
include high elevation basins as well as locations with thick snow
cover. Arizona enters higher pressure and a more zonal flow next
week which will help return temperatures closer to average.
&&
.AVIATION...For the 06Z TAF package...VFR conditions through TAF
period with mainly light north/northwesterly winds. Aviation
discussion not updated for TAF amendments.
&&
.FIRE WEATHER...Cold temperatures and dry continue through
Friday, with generally light north/northwest winds. Breezy
north/northeast winds are possible for Friday.
Saturday through Monday...Dry conditions with gradually warming
temperatures are expected through Monday. Winds will be light and
variable over the weekend into Monday.
&&
.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...Humphreys/BAJ
AVIATION...Humphreys
FIRE WEATHER...Humphreys/RKR
For Northern Arizona weather information visit
weather.gov/flagstaff
Area Forecast Discussion
National Weather Service Green Bay WI
909 PM CST Wed Dec 14 2022
New Information added to update section
.UPDATE...
Issued at 909 PM CST Wed Dec 14 2022
The latest RAP analysis and satellite imagery show a
large cyclone centered over the central Plains. A large, arcing
swath of precip is lifting north across Illinois and Wisconsin
this evening ahead of a potent PV anomaly located over Missouri.
Short range models have increased precip amounts slightly during
the overnight period. However, surface temps remain complicated
which leads to doubt about making significant changes to the
forecast. In particular, lower dewpoint air is moving into the
Door Peninsula as evident by cooling wet bulb temps. On the other
had, no signs of cooling temps across the southern Fox Valley
where there is some consideration of adding Waushara county into
the winter storm warning.
In the end, have decided to keep Door County into the warning
despite snow totals below warning criteria. More confident with
removing Kewaunee from the warning. Being on the cusp and no signs
of surface cooling yet, kept Waushara in the advisory as well.
Updated WSW already sent.
&&
.SHORT TERM...Tonight and Thursday
Issued at 258 PM CST Wed Dec 14 2022
This is a very complex forecast scenario, with several avenues by
which the forecast could run significantly off track. At the
heart of the problem is that we have strong, E-SE flow with fairly
substantial WAA through the low layers of the atmosphere and
thermal profiles which currently will support snow are mainly
W/NW of the forecast area. So in order to get heavy snow, profiles
across the area will need to cool despite the WAA. A surge of
strong lift heading NE into the area should be able to accomplish
that, but the question is how quickly it can occur. Have grown
increasingly concerned the changeover in E-C WI won`t occur until
late evening or around midnight. And even when temps aloft cool
sufficiently, boundary layer temps could be problematic as several
upstream METARs in Lower Michigan were now around 40F. Dew points
were also starting to increase, so evaporational cooling will
become increasingly limited. In addition, the band of heavy
precip associated with the lift will shift through the area
pretty quickly. The bottom line is, pulled back on snow totals in
E-C WI and delayed the start of the warning in Door/Brown/Kewaunee
and Outagamie until 03Z. That may not be enough, but should convey
the idea that anyone running errands early this evening should be
able to get them in before travel deteriorates.
Another area of concern is what will happen in central Wisconsin
as the wet snow begins to fall and stick to trees and power lines
that have up to a quarter inch of ice on them. Highlighted the
potential for power outages in the HWO, and will need to monitor
this situation closely during the evening.
Precipitation will taper to light snow and drizzle/freezing
drizzle during the day tomorrow as the mid-level dry slot wraps
into the area.
.LONG TERM...Thursday Night Through Wednesday
Issued at 258 PM CST Wed Dec 14 2022
The main two concerns for the extended will be the ongoing light
snow potential for the end of the work week through the weekend
and the inbound cold for next week.
Scattered light snow showers will be in place at the beginning of
the extended as the upper low continues to rotate over the area
Thursday night through Saturday. Scattered snow will bring
additional light accumulations up to an inch through the day
Friday. With a fairly saturated DGZ layer and some upper support
still in place for Saturday, increased pops there as well to bring
in at least isolated light snow showers, but currently expect any
additional accumulations to be minor. Any remaining snow will then
finally depart the region late Saturday into Sunday.
Much colder air will be set to follow the departing system Sunday
into early next week, with highs progressively falling into the
teens by Monday and Tuesday. Low temperatures during this period
could be below zero across the area. Long range models suggest a
brief warmup possible on Wednesday before below normal
temperatures return towards the end of next week.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 531 PM CST Wed Dec 14 2022
Widespread precip will move into the region from the south by mid
to late evening and continue into Thursday morning. Temperatures
will gradually cool, which will change a wintry mix to all snow by
late evening over central and north-central WI, and to all snow
early overnight across the Fox Valley and Lakeshore. Heavy snow is
then expected for a several hour period overnight before
intensity wanes early Thursday morning. LIFR to VLIFR flight
conditions are expected in the heavy snow that could produce
snowfall rates in excess of 1 inch per hour.
After the heavy snow exits, conditions will likely take until
midday or early afternoon to improve to MVFR at most locations
(perhaps until late afternoon for Rhinelander).
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 9 AM CST Thursday for WIZ005-010>013-
018>021-030-031-035>037-073-074.
Winter Storm Warning until 9 AM CST Thursday for WIZ022-038-039.
Winter Weather Advisory until 9 AM CST Thursday for WIZ040-045-
048>050.
&&
$$
UPDATE.........MPC
SHORT TERM.....Skowronski
LONG TERM......Uhlmann
AVIATION.......MPC
Area Forecast Discussion
National Weather Service Indianapolis IN
923 PM EST Wed Dec 14 2022
.Forecast Update...
Issued at 923 PM EST Wed Dec 14 2022
Little changes needed for the short term. HRRR was initialized well
with widespread showers all the way southwest to near Clarksville
Tennessee and Cape Girardeau Missouri. The HRRR takes this back end
into our far northeastern counties around 09z with showers exiting
as early as Midnight around Vincennes to 2 or 3 AM along the I-74
corridor. 45 knot low level jet, isentropic lift, frontogenesis and
synoptic lift from negatively tilted trough and occluded system were
all combining to produce areas of moderate rain.
With the inversion in place, winds were having a difficult time
tapping the low level jet and mixing down, but still think
eventually there will be some gusts to 30 mph late this evening and
early overnight.
Lightning trends don`t support adding thunder, but would not
completely discount a stray rumble.
&&
.Short Term...(This evening through Thursday)
Issued at 255 PM EST Wed Dec 14 2022
* Rain developing this evening, continuing in to tonight
* Gusty winds possible overnight
* Cooler temperatures arrive tomorrow
Rest of Today
Moisture trapped within a low-level inversion has persisted through
the day today. Patchy fog, occasional drizzle, and low ceilings have
therefore been the theme. Various BUFKIT soundings indicate that the
inversion should persist into the evening hours. Temperatures will
gradually rise through remainder of the afternoon into tonight as
warm air advection and thick cloud cover negate nocturnal cooling.
Tonight
A deep trough currently resides over the central Plains states, with
a closed low over the Dakotas. A shortwave trough rounding the base
of the larger-scale trough will pivot northward this evening. As the
shortwave amplifies it`ll begin to take on a negative tilt. At the
surface, a potent LLJ will redevelop allowing moisture to increase
from the south. As a result, widespread rainfall is expected to
develop as upper-level divergence increases, PVA is maximized, and
favorable jet dynamics align over low-level convergence and broad
isentropic lift.
Rain should begin between 22z-00z, and become more widespread as the
night progresses. The axis of the heaviest rain will likely occur
along and just to the west of the Illinois border, as that`s where
the aforementioned dynamics line up best. Further to the east, rain
will be a bit more showery in nature. Models show non-zero amounts
of CAPE overnight so embedded rumbles of thunder cannot be ruled out
given how much lift there will be.
Aside from the rain, a brief period of gusty winds is also possible
overnight. One important thing needs to go right for this to happen.
Namely, the low-level inversion has to erode away enough to allow
downward momentum transfer to occur. An intensifying surface low
associated with the shortwave will move northward out of the
Mississippi river valley, which will enhance the LLJ, tighten
surface MSLP gradients, and simultaneously increase low-level WAA.
Of these, the last one is key for eroding the inversion. The narrow
surface warm sector of the low is therefore where the best wind
potential lies. Wind gust timing looks to be 00-07z. Gusts should
remain well-below advisory threshold, generally 30-40 mph at most.
Tomorrow
Once the system swings through, winds will shift to southwesterly
and drier air moves in. Additionally, strong cold air advection will
set in, which will mark the beginning of a long stretch of cooler
weather. Breezy conditions persist tomorrow in the better mixed post-
frontal atmosphere, but with the low well to our north only
expecting gusts around 25mph.
&&
.Long Term...(Thursday night through Wednesday)
Issued at 255 PM EST Wed Dec 14 2022
Thursday Night Through Saturday.
The heavier precipitation will have come to an end Thursday night as
the aforementioned strong upper level low pressure system continues
to occlude and approach the Great Lakes region. This slow moving
low pressure system will keep a fairly persistent forecast in place
late Thursday night through Saturday with surface flow generally
southwesterly while flow aloft is generally easterly to somewhat
northeasterly.
Areas of weak to moderate vorticity circling around the low will
combine with the residual moisture from the midweek rains and very
steep lapse rates near the surface to create occasional flurries
through much of the latter portions of the week. Flurries will be
most frequent across the northern counties where the upper level
forcing will be stronger.
Sunday Through Wednesday.
The low will finally push away Sunday with zonal flow aloft during
the early work week. Temperatures will remain below normal with the
lingering cold air aloft and lack of southerly surface flow. The
pattern will begin to shift going into Wednesday as the next major
weather system nears the area, but there remains a significant
amount of uncertainty as to how and when this system will impact the
area.
Will put low chances for precipitation in, but think the better
chances will be Thursday into Friday. Regarding this system, snow is
looking probable to likely for portions of the Midwest going into
Christmas, but locations, timing, and amounts remain very uncertain.
&&
.Aviation...(00Z TAF Issuance)
Issued at 502 PM EST Wed Dec 14 2022
Impacts:
- IFR and worse conditions will improve to MVFR after 08z Thursday
as the widespread rain moves off
- Winds will be from 110-150 degrees and switch to 220-250 degrees
after 04z-06z with gusts to over 25 knots through 07z-09z
Discussion:
An occluded system will move through tonight with IFR worse
conditions, gusty winds and widespread rain through the early
morning. Conditions will gradually improve in the wake of the
system.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...MK
Short Term...Eckhoff
Long Term...White
Aviation...MK