Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/22
Area Forecast Discussion
National Weather Service La Crosse WI
959 PM CST Wed Dec 21 2022
.UPDATE...
Issued at 955 PM CST Wed Dec 21 2022
With the evening update, kept winter headlines in place. Snow is
ongoing-moderate at times with most visibilities in the 1 to 2
inch range. Early reports through mid to late evening have been in
the 1 to 2 inch range. At 9pm surface low pressure was centered
over northeast New Mexico with a weak surface low over northeast
Iowa and an inverted trough into northern WI and cold front
through southwest IA/northwest MO and much of Kansas. As the
trough deepens over the Plains, we will continue to see waves of
precipitation tonight through Thursday with the higher amounts in
the 5 to 8 inch range still on track for parts of western,
central, southwest WI and northeast Iowa. Northwest winds are on
track to increase Thursday, especially later Thursday afternoon
and Thursday night.
&&
.DISCUSSION...(Tonight through Wednesday)
Issued at 215 PM CST Wed Dec 21 2022
Key Messages:
- Winter Storm impacts into holiday weekend:
* snow tonight into Thu morning
* strongest winds Thu night-Fri night with widespread
blowing/drifting
* BLIZZARD conditions expected SE MN/NE IA Thu night
through Fri night
* Bitter to dangerously cold wind chills into Christmas
morning
Strong winter storm still on track to impact the area from tonight
into the weekend. Somewhat open trough as it swings across the local
area Thu, winding up/strengthening as it shifts northeast across the
new england states/southeast Canada. Recent model trends suggest a
bit quicker, farther northeast with the cyclone.
* SNOW: snow spreads west to east across the forecast area this
afternoon/early evening, persisting through the night then exiting
east for most during the morning/by noon. RAP soundings show a
deep DGZ from time to time tonight-Sat morning, upwards of 300-400
mbs. 20:1 ratios looks like a safe bet, potentially higher.
Amounts have vacillated a bit over the past few days based on
track of the storm/speed, related QPF. Latest outlay would drop
the higher amounts from NE IA into central WI with 6 to 8"
possible.
One interesting possibility is for some light snow/flurries to
develop off of lake Pepin/mississippi river Thu afternoon. The
NAMnest suggests this and given the fetch of winds and still some
open water, it could happen. Have opted to not include localized
snow chances as of now, and any amounts would be minor.
* WIND: winds start to crank up Thursday afternoon as the sfc low
lifts northeast across WI, potentially lingering well into
Saturday before a decreasing trend Sat night as pressure gradient
starts to relax with exiting of the storm/approach of sfc high.
Blowing/drifting impacts could be enough to continue warning
and/or and advisory for some locations through Sat afternoon.
Gusts still look to push into the 40s, flirting with 50 mph (still
possible).
With the additional several inches of fluffy snow, widespread
blowing and drifting snow is expected...with blizzard conditions
(1/4 mile vsbys) mostly over the open/unsheltered areas of southeast
MN/northeast IA. Have upgraded the Winter Storm Warning to reflect
these conditions for Thu night into Fri night.
Localized white-out conditions are possible elsewhere and do see
some increased potential for more widespread blizzard conditions for
some locations north of I-94 (Clark and Taylor county) and southwest
WI (specially Grant Co). An upgrade in the warning could become
necessary for these locations.
* COLD: dangerously cold wind chills expected from late tonight
through the holiday weekend. -20 to -40 F common during the late
night/morning hours through Christmas, coldest Fri and Sat
mornings. For now, will cover the cold impacts via the Winter
Storm/Blizzard warnings...but may need to go Wind Chill Adv into
Christmas morning as winter impacts focus mostly on the cold
(blowing/drifting snow impacts subside).
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 550 PM CST Wed Dec 21 2022
Periods of snow are expected this evening and into the overnight
hours. The more organized snow is moving into the KRST/KLSE areas
this evening with MVFR conditions dropping to IFR/patchy LIFR
visibilities and ceilings. Another wave will bring additional
snow later tonight into Thursday morning and this should mainly
affect KLSE. Light east to northeast winds shift to the northwest
and increase overnight. Northwest winds 10 to 20 mph with gusts 20
to 30kts Thursday. Due to the fluffy snow and increasing winds,
blowing snow is expected to develop with some visibility
reductions possible.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning until 6 AM CST Saturday for WIZ017-029-
032>034-041>044-053>055-061.
MN...Winter Storm Warning until 6 PM CST Thursday for MNZ079-086>088-
094>096.
Blizzard Warning from 6 PM Thursday to 6 AM CST Saturday for
MNZ079-086>088-094>096.
IA...Winter Storm Warning until 6 PM CST Thursday for IAZ008>011-018-
019-029-030.
Blizzard Warning from 6 PM Thursday to 6 AM CST Saturday for
IAZ008>011-018-019-029-030.
&&
$$
UPDATE...Zapotocny
DISCUSSION...Rieck
AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Dodge City KS
442 PM CST Wed Dec 21 2022
...Updated Aviation Discussion...
.SHORT TERM...(This evening through Thursday night)
Issued at 312 PM CST Wed Dec 21 2022
A warm front lifting north of the region resulted in low level
veering winds and warm air advection across our region this
morning and early afternoon. As a result, areas of dense fog have
gradually improved to above a quarter mile while freezing fog
deposition has piled up hoar frost on most surfaces. The HRRR
gradually erodes the dense fog from west to east in the afternoon.
A dense fog advisory for dense fog and freezing fog valid until 3
pm is being allowed to expire as visibility should continue to
gradually improve. GOES Sat imagery continues to show an eastward
track to the western edge of the very low cloud cover/fog layer,
and HRRR model soundings showed and drying of the near surface
layer in the T-Td spreads.
Attention then turns to this evening. The cold front slams
through the forecast areas between 00 and 06 UTC / or 6pm and
midnight. The falling temperatures, with dendritic production zone
closer to the ground will lead to efficient light snow given
rapidly increasing snow ratios and saturated column. NAM models
20:1 ratios behind the front while HREF combined probabilities
show the snow isn’t expected to drop visibility to more than areas
of a half mile at times from Wakeeney to DDC and Pratt.
Extreme cold air advection will then be the focus, combining
negative temperature tendency with the very strong gradient winds,
to collapse apparent temperatures to the -20 to -40 range. The
leading edge of the front will arrive per the NAM12 km in the mid
evening, and be through the entire area before midnight.
Gradient winds on Friday will maintain the cold wind chill risk
through the period of Friday morning. Though not as brutally
cold, the wind chills will still be in the warning category -
namely the 20 to 30 below zero area.
.LONG TERM...(Friday through Wednesday)
Issued at 312 PM CST Wed Dec 21 2022
By Saturday morning, the 0 to -15 below zero wind chills will
seem relatively balmy as temperatures remain near zero and winds
fall to around 10 mph as high pressure and less gradient plays a
part. Through the weekend, the cold air retreats eastward, as as
southwest boundary layer winds increase, bringing temps back above
freezing. From simply a pattern recognition standpoint, Tuesday
and Wednesday could be relatively warm days with mid level
shortwave ridging showing up in the models, but any warmup doesn’t
look sustained. In the meantime, we’ll look toward Sunday night
and Monday for "some" opportunity for light precipitation, either
rain or snow associated with a fast moving northwest flow
shortwave, somewhere is the central plains. Officially, a dry
forecast and if anything occurs, it wouldn`t be significant.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 431 PM CST Wed Dec 21 2022
Low stratus across eastern portions of the CWA continue to produce
LIFR ceilings and visibility at DDC and HYS with GCK and LBL still
VFR at this time. An approaching cold front will switch winds out
of the north between 03-05Z north to south gusting initially up to
35kts. Winds will increase to 40-45kt gusts after 07-09Z as cold
air advection helps to aid in the strongest mixing to the surface
post frontal passage. Ceilings will remain MVFR to IFR but
uncertainty on how low they will be. Snow will begin to fall
around HYS after 06Z through about 15Z with blowing snow a factor
due to the strong north winds. All other TAF sites will not see
influence to much if any snowfall only carrying VCSH near GCK and
DDC during this same time frame. Ceilings will begin to lift to
VFR after 15Z with improving conditions as the snow and system
lifts to the northeast. However, winds will remain gusting up to
35-40kts through the end of the period before diminishing at the
end towards sunset Thursday evening.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC -9 5 -7 17 / 40 30 0 0
GCK -10 4 -9 16 / 40 30 0 0
EHA -6 8 -6 19 / 20 20 0 0
LBL -7 7 -7 18 / 30 20 0 0
HYS -11 2 -10 14 / 90 30 0 0
P28 -2 7 -3 17 / 40 30 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
Wind Chill Warning from 9 PM CST /8 PM MST/ this evening to noon
CST /11 AM MST/ Friday for KSZ030-031-043>046-061>066-074>081-
084>090.
Winter Weather Advisory from midnight tonight to 6 AM CST
Thursday for KSZ030-031-043>046.
&&
$$
SHORT TERM...Russell
LONG TERM...Russell
AVIATION...Lowe
Area Forecast Discussion
National Weather Service Des Moines IA
543 PM CST Wed Dec 21 2022
...Updated for the 00z Aviation Discussion...
.DISCUSSION.../Tonight through Wednesday/
Issued at 355 PM CST Wed Dec 21 2022
Key Messages:
- Significant winter storm will bring blizzard conditions later
Thursday into early Saturday
- Blizzard conditions combined with dangerous wind chills will create
life threatening conditions for anyone that ventures out during
the worst of this storm
Details: GOES-East upper level water vapor imagery shows the trough
that will bring the high impact winter storm to the region moving
over the northern Plains. A lead shortwave cutting across the Ozarks
has broad isentropic ascent ahead of it and this has spurred light
snow across western Iowa that has reached I-35. 12z KOAX sounding
showed dry air in the 850-650mb layer and while there has likely
been some saturating in this layer, we are still seeing reports of
unknown precipitation. This is likely a bit of freezing drizzle with
the loss of ice introduction shown in the soundings. So, for a few
hours this afternoon into early this evening, parts of southern Iowa
may have freezing drizzle with a glaze/accretion of around 0.01"
possible. Otherwise, this event will be all snow. The isentropic
lift will move east through the rest of this afternoon into early
this evening with snow rates ranging between a quarter to three-
quarter of an inch per hour possible. Winds through this period will
generally be under 15 mph so very little blowing snow is expected.
There could be a slight lull later this evening before the arctic
cold front blasts its way through, which will bring another round of
snow with similar rates. Attendant to this boundary will be strong,
low level frontogenesis (fgen) in the 925-850mb layer, though even
stout fgen is in the 850-700mb layer. Forecast soundings show that
as the low and mid-levels of the atmosphere cool, more of the
saturated profile will be within the dendritic growth zone (DGZ; -
12C to -18C). Cross sections show lift in this layer generally as
weak to moderate; however, recent RAP runs do show stronger lift
passing through briefly. Snow ratios were blended up into the upper
teens given the depth of the DGZ and this is supported by Cobb
output from the NAM, GFS, and RAP. The latter two even show snow
ratios briefly into the 20:1s, which may be indicative of stronger
omega. Behind the front, low level kinematics will ramp up with
strong cold air advection beginning and modest pressure height rises
following. The quickening winds with gusts of 30 to 40 mph later
tonight into Thursday along with falling snow will lower visibilities
under a mile and at times and in some areas below a 1/2 mile. Most
of the snow with the fgen will have exited the area by midday if not
by mid-morning with snow accumulations of 3 to 6 inches common
across much of the area and highest in the northeastern portion of
the state. Overall, snow totals this round compared to the overnight
forecast were a half to perhaps an inch higher. Therefore, see no
reason to adjust the winter storm warning given expected impacts.
While the snow will have ended by midday Thursday, the impacts will
continue Thursday into Friday waning into Saturday as strong and
gusty winds persist. These winds will be due to the pressure
gradient strengthening over the region as surface low pressure
intensifies over the eastern Great Lakes. The strongest winds at
this time with gusts over 45 mph will be Thursday night into Friday.
With these winds and the recently fallen, blowable snow on the
ground, severe visibility restrictions are forecast and will be
worst in rural, open areas compared to any sheltered, urban areas.
We worked with our neighboring offices this morning to coordinate
the Blizzard Warning, which starts midday Thursday and goes until
Saturday morning, along and north of I-80. To the south, land use
and topography along with no existing snowpack raises questions
about whether blizzard conditions would materialize. However, we
will monitor in case confidence increases to expand the warning.
What makes this winter storm particularly dangerous and life
threatening is that wind chills for much of the period midday
Thursday into midday Saturday will be 30 below zero or less
(colder). Therefore, if you venture out trying to reach a
destination whether for local or holiday travel and become stranded,
frostbite could set in within minutes. Therefore, travel Thursday
through Friday is strongly discouraged for your safety.
As the mid-level trough and surface low pressure begin to pull away
from the area on Saturday, winds will begin to lessen, but areas of
blowing snow will still be possible with sustained winds of 15 to 25
mph and gusts of 25 to 35 mph still persisting. So, while conditions
may not be blizzard, travel impacts could still remain and hamper
travel on Saturday. Higher heights will move over the region this
weekend and this will allow temperatures to moderate Christmas Eve
into Christmas Day and early next week. However, the flow over our
region will remain from the northwest on the backside of the trough
and deterministic and ensemble guidance still shows a clipper system
dropping through later Sunday into Monday, which could bring light
snow to the state.
&&
.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 543 PM CST Wed Dec 21 2022
Poor aviation weather is expected for the duration of the forecast
with snow and IFR to LIFR conditions overnight from low ceilings
and visibilities. Strong northwest winds arrive behind an arctic
front overnight and persist for the remainder of the forecast.
This will produce extensive blowing snow with low visibilities
persisting into Thursday and beyond.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until noon CST Thursday for IAZ004>007-
015>017-023>026-033>037-044>048-057>059.
Blizzard Warning from noon Thursday to 6 AM CST Saturday for
IAZ004>007-015>017-023>028-033>039-044>050-057>062.
Winter Storm Warning until noon CST Thursday for IAZ027-028-038-
039-049-050-060>062.
Winter Storm Warning until 6 AM CST Saturday for IAZ070-071-081.
Winter Storm Warning until 6 AM CST Saturday for IAZ072>075-
082>086-092>097.
&&
$$
DISCUSSION...Ansorge
AVIATION...Cogil
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1043 PM EST Wed Dec 21 2022
.UPDATE...
Issued at 1043 PM EST WED DEC 21 2022
This evening we are starting to see some returns on the WSR-88D
radar, but these are likely not reaching the ground or are
sprinkles at most given the 20 degree dewpoint depression that we
are seeing at the surface in most locations. The column will
moisten through the night and eventually this will fall in the
form of rain. The questions in the deeper valleys remains from
previous discussion, but seem less likely given we have seen
clouds quickly modify these colder valleys. Opted to adjust the
PoP grids some to align with trends and closer to the NBM hourly
PoPs. Outside of those minor changes overall not much was changed
for this update.
The 00Z data is just now starting to trickle in for some of the
CAMs. In terms of the arctic cold front, the HRRR and ARW remain
much faster with the arrival of the cold air when compared to
other guidance and in general it seems the guidance can bring
these kinds of airmass changes in too fast. The HRRR also remains
quite the outlier in terms of just how cold the 2 meter
temperatures get in the wake of the surface front early Friday
morning and the ARW shows similar colder air even though not as
cold. Thinking these are big outliers and not to keen on putting
too much stock in these solutions at this point. Will let the
overnight shift further investigate the forecast and make any
modifications, as none are planned on this shift.
UPDATE Issued at 716 PM EST WED DEC 21 2022
The evening surface analysis reveals a weak warm front or surface
trough from the Mid South into PA. An upper level shortwave is
helping to increase clouds this evening at mainly the mid and high
levels. This is noted with sheltered valley temperatures already
dropping into the lower 30s. We will see an increasing 850mb jet
through the night and this will help to moisten the column in a
top down manner. This coupled with some decent lift within the
lower levels will eventually lead to some rain late tonight into
Thursday morning. The issue with this is how do the deeper
valleys modify through the night because we will see the outside
potential for this rain to fall into sub-freezing valley
temperatures. Right now thinking the deeper valleys will modify by
the time we moisten enough to see rain falling, but this will be
monitored closely through the evening. Also, looking at road
temperatures that are still well above freezing at this point.
Only minor changes were needed to the current forecast grids to
account for the latest obs and trends.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 512 PM EST WED DEC 21 2022
Two systems will affect the region during the short term period.
The first of these will affect us tonight into Thursday, and the
second and by far most significant one will hit Thursday night.
Late this afternoon, a massive upper level trough was amplifying
over the middle CONUS. A shortwave trough moving through the east
side of this trough will pass over the Ohio Valley and southeast
CONUS tonight and early Friday, supporting coastal surface low
development along the southeast coast. Light precip from this
will probably make it as far northwest as eastern KY. Valley temps
will fall off steeply this evening before clouds thicken, but
probably creep higher later in the night. There is some concern
that light rain could fall into subfreezing valleys before they
warm up, but the probability is low. The situation will need to be
watched, though. Any meaningful rain with this system will lift
out to the northeast during the day Thursday.
The main event will come on Thursday night in association with an
anomalously deep storm system passing to our north. The extremely
intense low will send an arctic cold front through our area on
Thursday night, crashing temperatures on brisk winds, and bringing
a fast round of precip near the front. It will probably start as
rain, but quickly transition to snow. Forecast soundings indicate
elevated instability lingering after the change to snow, which
raises concerns for brief intense snowfall rates and locally
elevated accumulations. Accumulations will be tricky. The ground
will not be frozen at the onset, and snow will tend to initially
melt from the bottom up as it falls. Strong winds will also tend
to favor lower ratios than would otherwise be expected. Best
estimates for amounts, based on expected precip after the
changeover, is generally 1 to 2 inches.
The aforementioned strong winds will also cause some blowing
snow, and produce very cold wind chills once temps fall off. The
coldest wind chills are forecast in the long term period on
Friday, but readings will be in advisory criteria before dawn, and
a Wind Chill Watch was started late Thursday night to cover the
onset of the hazard before the potential of warning criteria.
.LONG TERM...(Friday through Wednesday)
Issued at 353 PM EST WED DEC 21 2022
Key Concerns:
1. Bitterly cold temperatures in the single digits (above and
below zero) in combination with strong winds will lead to wind
chills of -15F to possibly as cold as -25F (-25F to -35F above
2,000 feet) late Thursday night through early Friday afternoon;
then -10F to -20F (-20 to -30F above 2,000 feet) through Saturday
morning.
2. Westerly winds of 15 to 25 mph will gust to between 30 and 40
mph on Friday into Friday night, potentially leading to a few downed
limbs/weak trees and isolated power outages.
3. Blowing and drifting of freshly fallen snow likely Friday into
Friday night, especially in open areas.
4. Bitterly cold, albeit moderating, temperatures persist through
the remainder of the Christmas weekend.
Arctic air will become entrenched over Eastern Kentucky on Friday.
The 21/12z model suite analysis shows a deep closed low to our north
on Friday morning. The arctic front will be well east of the area by
12z, leaving just some lingering snow showers and flurries. There
are still some minor differences in the depth and track of the
arctic upper low. Of the deterministic solutions, the GFS is fastest
and most southerly with the ~507 dam low over Central Ohio while the
Canadian is slowest and shallowest, lagging the ~512 dam low just
southwest of Lake Michigan. ECWMF shows a compromise between the
two, through closer to the Canadian. The low pivots back to the
north over the weekend ending up near James Bay on Sunday. An
unusually deep surface low reflection will start the period
somewhere over the Eastern Great Lakes before lifting north and
becoming vertically stacked under the upper system on Christmas.
Rising heights and associated subsidence supports high pressure
building over the Ohio Valley by Sunday evening/night.
With these track/strength differences, there is still some
uncertainty in the magnitude of the post-frontal winds and air
temperatures over Eastern Kentucky on Friday. Most of the guidance
shows 925mb temperatures of -15 to -24C (east to west) at 12z
Friday, though there is a colder trend especially in the hi-res
guidance. The recent 15z RAP13 guidance is beyond that coldest
end of the spectrum with -25 to -28C 925mb temperatures. This is
currently an outlier solution that would lead to extreme cold and
the brutal wind chills which are being depicted by the HRRR due to
its ingestion of RAP13 data. Stuck with the better model
consensus which would support temperatures single digits near and
above zero, at best, through the day on Friday. In addition, steep
low-level lapse rates and a strong surface pressure gradient will
support robust mix down of winds up to the 850 mb level. There is
considerable model spread on the strength of the winds at 850 mb,
ranging from as little as 20 to 30 knots in the Canadian to 40 to
50 knots in the RAP/GFS (the location of the low will prove
pivotal). Given the rather large spread, favored the NBM blended
sustained wind speeds, which have diminished slightly in the last
24 hours. The still results in wind chills of right around -25F
for many of the ridges and colder than that for the higher
mountains. Given only moderate forecaster confidence for
sufficient wind speed, opted to issue a Wind Chill Watch for the
entire forecast area and allow the night shift to assess upstream
observations and the 00z model suite. The NBM blend favored
westerly wind gusts of 30 to 40 mph on Friday into Friday night.
Winds of this magnitude may be sufficient to knock down weaker
trees and smaller limbs, potentially leading to isolated power
outages. Any loose snow will blow and drift, especially across
north-south oriented highways in exposed terrain. A Wind Advisory
for gusts and Winter Weather Advisory for blowing snow may be
needed for portions of the area. Lingering low-level moisture will
also lead to light flurries, but expect little
impact/accumulation given negligible lift and temperatures too
cold for dendrites. Temperatures on Friday night are expected to
hold in the single digits above (below zero above 2,000 feet) with
abundant cloud cover and a well-mixed boundary layer.
The winds will lighten somewhat on Saturday and more so on Sunday as
high pressure builds in. BUFKIT momentum transfer supports wind
gusts of 20 to 30 mph (up to 35 mph across higher ridges) on
Saturday while the 925 mb temperatures moderate to between
between -12 and -18C. Cloud cover should diminish as the CAA
eases. Despite some sunshine, it will still be bitterly cold with
highs only in the teens. The wind chills will still be frigid,
keeping apparent temperatures in the single digits above and below
zero at the warmest part of the afternoon. Christmas Day will
still be cold, highs in the 20 to 25 degree range, but with less
wind, it should feel notably "warmer".
The frigid air mass will continue to retreat early next week as the
pattern swings back toward more seasonable norms. It remains to be
seen whether the pattern transitions quietly or with some kind of
storm system. There are some hints of another much shallower
trough dropping through the region on Tuesday. Various
deterministic and ensemble members show a wave of low pressure
developing in the lingering baroclinic zone; however, the
existence, track, strength and impacts of such a system remains
highly uncertain due large model spread.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 641 PM EST WED DEC 21 2022
VFR skies are the story to begin the period. We will see top down
moistening tonight, as a upper level wave moves east and a low
level jet increases through the night. This will lead to lowering
Cigs and increased chances of rain. The Cigs will lower into the
MVFR levels toward dawn Thursday and could lower further depending
on how precipitation evolves. The winds will generally remain
under 5 knots through the period, but will begin southeast and
become more south southeast by Thursday afternoon.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM Thursday to 9 AM EST Friday
for KYZ044-050>052-058>060-068-069-079-080-083>088-104-106>120.
Wind Chill Watch from late Thursday night through Friday
afternoon for KYZ044-050>052-058>060-068-069-079-080-083>088-104-
106>120.
&&
$$
UPDATE...DJ
SHORT TERM...HAL
LONG TERM...GEERTSON
AVIATION...DJ
Area Forecast Discussion
National Weather Service Memphis TN
932 PM CST Wed Dec 21 2022
...New UPDATE...
.UPDATE...
Issued at 930 PM CST Wed Dec 21 2022
The arctic front is storming across Kansas at this hour. That
dangerous cold air airmass is heading for the Mid-South. The front
will arrive in NE AR just after noon and reach Monroe County MS
only 6-7 hours later. Cold air will build quickly. Still not
expecting a whole lot of rain ahead of the cold front. Most of the
precipitation will be along and behind the front. Latest data
indicates that a 180 kt jet will dig into base of the upper trough
over the MS Valley Thursday afternoon. This places at least the
northern half of the Mid-South in a favorable area for strong lift
while some deeper moisture remains over the area. This feature is
a tad further south of previous model runs which should bring the
accumulating snow a little further south. Latest model soundings
show a 2-3 hr period where the profile is saturated and well below
freezing. Northern areas have favorable profiles for about 3 hrs
while further south toward Memphis...maybe 2 hours. The latest
guidance has trended toward a little more snow which makes sense
given the slightly further south position of the digging jet. QPF
amounts are slightly higher than 24 hrs ago across the region
probably due to the additional lift generated by this more
favorable position. HRRR depicts 2-3 hrs of surface vsbys below
one mile with areas down to 1/4 mile across the Bootheel. Given
the trends in the latest data decided to bump snowfall totals up a
bit with more than an inch north of a line from Jonesboro to
Lexington, TN. Closer to 2 inches is likely along the KY border.
Keep in mind that precipitation will start out as rain. Rain will
likely cause wet roads. The cold air will rush in with temps
dropping quickly and rain will quickly change to snow. Snow may
melt initially due to a relatively warm ground but it will not be
long before everything flash freezes. Driving could become very
hazardous. It is a great idea to stay off the roads while this
front and associated rain/snow moves through.
The cold will be unbelievable to folks that do not wander north
during the winter. This is historic cold. Wind chill values of -10
to -20 will be common Thursday night. Wind chills values this low
have not happened in recent memory in the Mid-South. Winds gusts
of 35 to 45 mph could cause a few power outages and areas of
blowing snow. Now is the time to make plans and prepare.
&&
.DISCUSSION...
(This evening through next Tuesday)
Issued at 353 PM CST Wed Dec 21 2022
Bottom line up front: winter will arrive tomorrow in the Mid-South
in the form of extremely cold temperatures, flash freezes, and a
light dusting to an inch of snow accumulation.
One more day of benign weather with cool temperatures is on tap
today due to quasi-zonal flow aloft. Tomorrow, an incredibly deep
trough will dig down into the Tennessee Valley. Its associated
Arctic cold front will move through late afternoon tomorrow,
plunging temperatures below freezing quite rapidly post-FROPA.
Though the rainfall ahead of the front is expected to be fairly
light, there is a flash freezing threat due to the rapid plunge in
temperatures. We could see as much as a 40 degree drop in
temperatures in a matter of hours behind the front tomorrow. To
account for this, while a bit unorthodox, we issued a Winter
Weather Advisory for much of the Mid-South.
The Winter Weather Advisory from noon tomorrow through 6AM Friday
is in two segments for two separate purposes. The northern portion
along the AR/MO and TN/KY state lines is for snow accumulations
around 1 inch. Most of the CWA will only see a light dusting of
snow, but areas farther north could see isolated pockets of 1-2
inches. The southern portion of the Winter Weather Advisory south
of a Jonesboro, AR to Camden, TN line is specifically for the
potential for a rare flash-freeze. This may result in hazardous
travel conditions as the rapid temperature drop could cause a thin
coating of ice from any residual moisture on the ground.
The wind chills overnight tomorrow night remain the big story for
this forecast package. The Wind Chill Warning and Advisory headlines
remain unchanged; still expect wind chills in the
-10 to -20F area wide by Friday morning. This is due in part to the
brisk northwest winds on the back side of the Arctic front, gusting
up to 40 mph overnight tomorrow night into Friday morning. Power
outages could become an issue with these strong winds knocking down
trees/branches onto power lines. The key message: single digit
temperatures and strong northwest winds will make for brutally cold
wind chills tomorrow night after the front passes.
Another important note is that we`re expecting several days of sub-
freezing temperatures. This is no ordinary Arctic front; once temps
take a plunge late tomorrow afternoon, most areas will not climb
back above freezing until early next week. With it being a holiday
weekend, we`re erring on the side of caution with our headlines to
make sure we get the message across that winter is coming tomorrow.
After the Arctic air finally migrates off to the east by next week,
temperatures begin to moderate again as midlevel ridging returns as
the dominant pattern. A few deterministic models are trying to bring
another weak system in on Monday, but confidence was too low to
include any PoPs in the forecast. Something to watch in the coming
days.
CAD
&&
.AVIATION...
(00Z TAFS)
Issued at 501 PM CST Wed Dec 21 2022
IFR conditions will prevail through the TAF period. Current MVFR
CIGs will deteriorate late tonight and show no improvements
through the period. A front will push through the region Thursday
afternoon bringing the potential for gusty winds starting around
18z. Showers will push through with the front we could see a brief
period of sleet before all changes over to snow. Expect snow to
only last for a few hours, then to change over to light rain after
the TAF period.
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...Winter Weather Advisory from noon Thursday to 6 AM CST Friday
for ARZ009-018-026>028-035-036-048-049-058.
Wind Chill Warning from 6 PM Thursday to noon CST Friday for
ARZ009-018-026>028-035-036.
Wind Chill Advisory from 6 PM Thursday to noon CST Friday for
ARZ048-049-058.
MO...Winter Weather Advisory from noon Thursday to 6 AM CST Friday
for MOZ113-115.
Wind Chill Warning from 6 PM Thursday to noon CST Friday for
MOZ113-115.
MS...Winter Weather Advisory from noon Thursday to 6 AM CST Friday
for MSZ001>005-007-008-010>013.
Wind Chill Warning from 6 PM Thursday to noon CST Friday for
MSZ001>006-009.
Wind Chill Advisory from 6 PM Thursday to noon CST Friday for
MSZ007-008-010>017-020>024.
TN...Winter Weather Advisory from noon Thursday to 6 AM CST Friday
for TNZ001>004-019>022-048>055-088>092.
Wind Chill Warning from 6 PM Thursday to noon CST Friday for
TNZ001>004-019>022-048>055-088>092.
&&
$$
PUBLIC FORECAST...SJM
AVIATION...SWB
Area Forecast Discussion
National Weather Service Raleigh NC
945 PM EST Wed Dec 21 2022
.SYNOPSIS...
Low pressure off the Southeast coast will move northward across the
eastern Carolinas and Mid Atlantic coast Thursday and Thursday
night. An unusually strong Arctic cold front will blast through the
region early Friday.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 945 PM Wednesday...
A weak surface low off the Florida coast will slowly deepen as it
inches its way north overnight along the coastline. Radar echoes
have been steadily increasing through the evening, although
measurable precipitation has remained south and west of the Triangle.
In most locations outside of the Triad, temperatures will stay
relatively constant through the night, changing little or slightly
rising. However, in the Triad there will likely be a little bit of
evaporative cooling as rain moves in and saturates the lower levels
of the atmosphere where the dewpoint is currently below freezing.
That being said, temperature observations have trended a few degrees
above the forecast temperature, and with the wetbulb zero line being
north of the Triad, think that despite any cooling that does occur,
there is enough of a warm nose aloft that any precipitation that
falls in the Triad should manage to remain all liquid. At this
point, have gone ahead and removed any mention of non-rain
precipitation in Forsyth and Guilford Counties.
&&
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 244 PM Wednesday...
The surface low over eastern SC is forecast in the guidance to
deepen to 1009-1008 mb as it tracks roughly up along/east of the
Triangle, roughly between US-1 and I-95, reaching far eastern VA by
the evening and off the Mid-Atlantic by early Fri. Deep ascent with
the upper-trough/jet and isentropic/WAA ascent is poised to maximize
during the day, tapering off from southwest to northeast by 18-21Z.
This pattern will favor likely rain in the morning, with a end to
precipitation from southwest to northeast by the early afternoon in
the west and early evening in the east as a dry slot pushes in with
the upper trough over the Mid-Mississippi Valley. Thereafter, some
light drizzle is possible with the low-level remaining saturated.
The coastal warm front is forecast to be somewhere around the I-95
corridor, where some weak surface based parcels in this small warm
sector could favor a marginal (level 1 out of 5) risk of damaging
winds. There exists poor lapse rates in this area with only modest
daytime heating, which should keep instability weak. However, low
and deep-layer shear is forecast to be quite strong, which could
also favor a minor tornado threat. The better tornado threat should
remain offshore where greater low-level moisture is available with
middle 60s dewpoints.
As for highs, there will be quite the west to east gradient. The
Triad and western Piedmont will be within the in-situ CAD wedge with
upper 30s to lower 40s. The eastern Piedmont/Sandhills and Coastal
Plain will be in the middle 50s to perhaps low/middle 60s. A narrow
corridor in the Triangle will see highs in the mid to upper 40s,
dependent on how far west the warm front penetrates.
After a lull in precipitation Thu evening, rain showers are forecast
to build back in, especially across the west into early Fri as the
strong upper-trough over the Midwest becomes negatively tilted as it
rotates into the Ohio Valley early Fri. The arctic front will also
favor additional frontogenetical forcing. Model guidance continues
to show some differences on the timing of the Arctic front. The
CMC/NAM are slowest, showing the front just west of the Triad by 12Z
Fri. The ECMWF and especially the GFS are faster, bringing it
through the western Piedmont at this same time. Some of the high-res
HRRR/NEST is also mixed, with the HRRR faster than the NEST. Some of
this uncertainty may be related to how fast the cold Arctic air can
move over the mountains of western NC, which usually tends to be
slower than what models depict. Given this uncertainty, currently
have lows reaching the middle 20s to upper 40s from NW to SE toward
daybreak Fri, roughly a blend of the guidance. Temperatures ahead of
the front will likely remain in the low to upper 40s/50 in the
southwest flow.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 350 PM Wednesday...
A strong Arctic front will sweep through central NC on Friday
morning with very gusty winds and dangerously cold wind chills
behind it...
A deep mid/upper low will move from IL/IN/OH on Friday morning NE
into New England and SE Canada by Friday night. The associated ~980
mb surface cyclone initially over the lower Great Lakes will push
NNE and occlude through the day, dragging a strong Arctic cold front
to its south. The front will be associated with a band of light
precipitation on Friday morning, with the best chance across the
north where POPs are slight to low chance. Model guidance continues
to trend faster with the frontal passage, but there is still some
disagreement on the exact timing. The GFS is slightly faster than
the ECMWF, while the NAM is on the slow end of all guidance and the
HRRR/RAP are on the fast end. The official forecast is faster than
NBM and reflects the middle GFS/ECMWF solution, bringing the front
through the Triad just before daybreak, the Triangle around early to
mid morning, and the Coastal Plain by mid to late morning. Soundings
show a few snowflakes can`t be ruled out across the north right as
the precipitation is ending on Friday morning, but typically these
scenarios where the cold air is chasing the precipitation result in
very brief snow if any, and no impacts are expected. A much bigger
impact will come from the strong winds along and behind the front,
and Wind Advisories will likely be needed. Model soundings show
potential for 45-55 mph wind gusts to mix down to the surface as the
front is passing through, with continued gusts of 35-45 mph possible
through the rest of the day behind the front. This will result in
very strong CAA with temperatures dropping into the 20s and 30s
through the day, as well as wind chills dropping into the teens and
single digits. With 1000-850 mb thicknesses dropping by as much as
100 m from early Friday to early Saturday, actual air temperatures
will likely drop into the lower-to-mid-teens everywhere across
central NC on Saturday morning, with statistical guidance now even
showing upper single digits in the far NW. This may threaten the
record low temperature of 14F on 12/24 at FAY. While winds will
relax some on Friday night, they will still be strong enough for
widespread wind chills from 0 to 10 below zero, so a Wind Chill
Advisory will likely be needed.
Very dry air will filter in through the weekend as surface high
pressure builds in from the west, so skies will be mostly clear and
no precipitation is expected. High temperatures on Saturday will
only be in the upper-20s to mid-30s, or 20-25 degrees below normal.
This will threaten the record low maximum temperatures for 12/24 at
GSO (28F) and RDU (29F). Winds will be in the 10-20 mph range
(gusting to 20-30 mph) and decreasing through the day, but this will
still be enough to keep maximum wind chills on Saturday in the teens
to lower-20s. 1000-850 mb thicknesses will then increase by around
20 m from Saturday to Sunday as the Arctic air mass begins to
moderate a bit, but very cold lows in the teens are still forecast
in many areas again Saturday night, as good radiational cooling will
help compensate for the higher thicknesses. Highs on Sunday will
still only be in the 30s, making for a very chilly Christmas Day.
The good news is the winds will significantly diminish by then so
the wind chills won`t be quite as low.
The Arctic air mass will continue to moderate on Monday and Tuesday
as the mid/upper trough lifts north into Canada. Even still,
temperatures are expected to be cooler than normal with low-level
thicknesses only increasing by 10-15 m each day. Models also show a
weak shortwave diving south into the MS Valley on Monday, reaching
the Deep South or northern Gulf of Mexico and moving off the
Southeast US coast on Tuesday or Wednesday. The 00z ECMWF and a
minority of its ensembles gave us precipitation from this system,
but the 12z ECMWF is more like the GFS in keeping the system
suppressed off the coast. For now just introduce slight chance POPs
in the south and east.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 722 PM Wednesday...
Adverse aviation conditions are likely across central NC starting
later this evening. Patchy light rain and attending MVFR cigs
continues to shift to the N and NW early this evening, and this rain
will gradually fill in and become more steady and heavier by later
this evening. This will bring cigs down to MVFR then quickly to
IFR/LIFR late this evening into the overnight hours, with MVFR to
IFR vsbys in steady rain. There is a small chance of patchy freezing
rain over INT/GSO for a few hours near and just after midnight,
however the chance of this is low, and anything that occurs would be
limited to elevated surfaces with little to no accrual. Rain and
IFR/LIFR conditions will remain dominant later tonight through mid
afternoon Thu across the entire area, along with low level wind
shear produced by 2kft winds from the SE at 40-50 kts atop surface
winds from the NE at or below 10 kts. There is a small chance for an
isolated thunderstorms near FAY/RWI late Thu morning into early
afternoon, but the risk is too low to include in the terminal
forecast at this time. Rain will end from SW to NE during mid to
late Thu afternoon across central NC, bringing vsbys up a bit,
although IFR/LIFR cigs are likely to persist through Thu evening.
Looking beyond 00z Fri: Sub-VFR conditions are likely to remain
dominant through much of Thu evening and night. While cigs/vsbys
should be lifting and trending toward VFR late Thu night into early
Fri morning, the strong / gusty / shifting winds will increasingly
become problematic as a powerful arctic cold front approaches then
sweeps east through central NC. Sustained winds from the W at 20-27
kts will frequently gust to 35-48 kts from late Thu night through
Fri afternoon with clearing skies and plunging temperatures. VFR
conditions with few clouds and diminishing winds but cold temps are
expected Fri evening through Mon. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Kren/MWS
NEAR TERM...Green
SHORT TERM...Kren
LONG TERM...Danco
AVIATION...Hartfield