Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/14/22
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
844 PM CST Tue Dec 13 2022
Issued at 840 PM CST Tue Dec 13 2022
The main band of pcpn has shift up into ND this evening as dry
slot overtakes the forecast area. Soundings continue to support
patchy fzdz and light snow overnight, but most of the accumulating
snows have probably ended for the time being. Overnight lows look
fine and relatively mild.
.SHORT TERM...(This Evening through Wednesday Afternoon)
Issued at 350 PM CST Tue Dec 13 2022
The main forecast challenges include how heavy the snow (snow rates)
will be this afternoon through late this evening with this current
band of precipitation moving through, and then whether or not any
drizzle/freezing drizzle potential will exist behind this
precipitation band tonight into Wednesday with the dry slot that
At 2 PM CST, skies were overcast and a significant band of moderate
to heavy snowfall was noted lifting north and west across the CWA.
Thunder is mentioned in the forecast across the western forecast
zones (west of the James River valley) through late this evening.
The classic high end lift/high end forcing signal in RAP model cross
sections describing heavy/intense snow bands is showing up right now
with this band of precipitation moving through. Add to that some
very unstable "cold air instability" values of -EPV* and fully
expecting to see this large band of snow evolve to smaller embedded
heavier bands of snow, and perhaps even some lightning and thunder.
Temperatures have remained nearly steady, generally between 30 and
34 degrees. East winds ranging from 15 to 25 mph with gusts to 35
mph are occurring across the Prairie Coteau into west central
Minnesota. Across the Missouri River valley westward, winds are more
north or northeast for direction between 10 and 20 mph for the most
There has been a lot of icing on and east of the Prairie Coteau
between last night and early this afternoon (CC on KABR working well
to differentiate between freezing rain areas and snow areas since
RAP/HRRR output seems to be struggling with the strength of the mid-
level WAA warm nose). The consensus, though, remains that the
thermal profile should be gradually transitioning from a dominant
freezing rain p-type to more of a dominant frozen p-type across the
eastern forecast zones by early this evening while this more
significant band of precipitation works through the region.
Regarding the dry slot that takes over behind this band of
precipitation, opted to replace any mention of "rain or freezing
rain" and run with "drizzle or freezing drizzle" given there should
only be a supercooled stratus layer to work with after the
saturation layer aloft goes away. And, that`s presuming the "clear
all the way down to the ground" slot of air showing up in satellite
imagery over Nebraska doesn`t make an appearance up in this CWA.
On Wednesday, the 500hpa low moves from near O`Neill, Nebraska to near
Vermilion, South Dakota (so, in other words, very little!!). Will
have to keep a watchful eye on the area north and northeast of
the 500hpa low center to see if/when the "cold air instability"
reduction zone becomes active again on Wednesday. It`s a mixed
signal amongst the models whether or not that area becomes active.
The 12Z HREF output hints a little bit at the potential for there
to be some areas of our southern/eastern forecast zones that see
snow rates potentially at or above 0.5in/hr on Wednesday. Did lean
on the NBM90th percentile and NBM4.1 (50/50 blend) for the
winds/gusts tonight and Wednesday. Seeing some of those stronger
winds/gusts spilling over into the west river/MO River valley
forecast zones by early Wednesday afternoon.
Limited low level thermal advection changes over the next 24 hours.
The far western forecast zones should be dropping out of the low 30s
and into the 20s from late tonight through the day on Wednesday.
No changes planned to the current headlines. Letting the Ice Storm
Warning stand on its own until 6PM (would like to see the CC values
transition to snow before dropping) and then transition over to a
Winter Storm Warning. All the rest of the CWA in a Winter Storm
Warning will continue to remain in said Winter Strm Warning.
.LONG TERM...(Wednesday Evening through Tuesday)
Issued at 350 PM CST Tue Dec 13 2022
Weather conditions will continue to revolve around the ongoing
winter storm that will be remaining in the vicinity of the region
through the first couple of days of this forecast period. Challenges
will continue to be winds and related blowing snow/visibility
impacts and p-types initially in the period followed by temperatures
toward the end of the term.
Starting things off Wednesday night, sfc low pressure and it`s
mid/upper level reflection will be situated around the NE/SD/MN/IA
border region. This system is progged to shift gradually eastward
across IA/MN region during the day Thursday and then eventually into
WI and the western Great Lakes region by late Thursday into Friday.
Shortwave energy will continue to rotate from east to west/southwest
across our FA; around the north and west side of the mid-lvl low
Wednesday night through Thursday...and to somewhat of a lesser
extent on Thursday night into Friday. So, precip chances will remain
relatively high through Thursday night before we see a gradual
drawdown in chances during the day Friday. This storm system will
continue to lift out to the northeast into Canada and farther away
from our area during the course of the weekend. Sfc high pressure
will build into our forecast area Saturday into Sunday and
prevailing through the end of the period. This will lead to drier,
but much colder conditions setting in.
Look at the precipitation more closely through the first couple days
of the period. There`s still some possibilities that some of our
eastern zones will see some pockets of freezing rain or freezing
drizzle Wednesday night into Thursday morning. This would especially
be the case across the higher elevations of the Prairie Coteau and
surrounding areas of northeast SD/west central MN. It`s not expected
to be as impactful though as it was in those areas today. The
transition to more snow will be the trend across our eastern zones
on Thursday and for the remainder of the event through Friday.
Additional accumulations of snow will be more probable across
eastern zones where another 3 to 6 inches could fall between
Wednesday night and Friday. Farther west, from the James Valley
through West River zones, precip will be all snow for the duration
of the event. We might see more pockets or bands of snow across our
western zones versus more widespread activity Thursday into Thursday
night. Accumulations will generally be lighter or lower across the
west through the end of the event.
One of the challenges mentioned above will be wind speeds and the
resultant impact they will have when it comes to blowing snow and
reduced visibilities. Wednesday night into Friday morning still look
to be the window for winds to increase substantially, especially
west of the James Valley through West River zones. There will be
modest cold air advection starting to take place West River and
Missouri Valley areas late Wednesday through Thursday. The gradient
tightens noticeably across central SD during this time. Ensemble
probabilities of seeing max gusts in excess of 40 kts still remain
the highest across portions of the Missouri Valley and southwestern
sections of the CWA. So, expecting some impactful conditions in
either falling snow or from the blowing around of the fluffier snows
that have accumulated on the surface. We`ll have to continue to
monitor these trends over the next 24 hours in case a change from
current headlines is warranted.
Finally, temperatures will remain rather mild through the end of the
week. A much colder airmass is expected to advent into our region
during the course of the weekend. Well below normal temperatures are
expected by early next week. Expecting overnight lows will be well
below zero and daytime highs will struggle to make into the single
digits to low teens.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 507 PM CST Tue Dec 13 2022
IFR/MVFR cigs are expected through the night. Meanwhile a band of
snow will move from south to north over the area this evening
before pushing off into ND. Heavy snow in that band could reduce
vsbys to 1/4sm or less at times for KMBG/KABR/KATY through mid
evening. Improvement is expected thereafter.
SD...Winter Storm Warning until 6 AM CST /5 AM MST/ Thursday for
MN...Winter Storm Warning until 6 AM CST Thursday for MNZ039-046.
Area Forecast Discussion
National Weather Service La Crosse WI
835 PM CST Tue Dec 13 2022
Issued at 830 PM CST Tue Dec 13 2022
Main update this evening focuses on the increasing (60-70% chance)
of a band of moderate to even heavy snow forming from west of
Rochester and lifting northeastward north of Winona and then into
western Wisconsin between 08-14Z. The high resolution guidance
(RAP/HRRR) have been steadfast that the warm nose along this
corridor collapses with the arrival of a second band of
precipitation after 06Z. This band is lifting northward through
southern Iowa/northern Missouri this evening with multiple
lightning strikes noted as it crossed the IA/MO border. The HRRR
and RAP forecast profiles both show a token (10-30 J/kg) of
upright convection above the dendritic growth zone with very
impressive synoptic lift through this corridor as well.
All combined, these ingredients point to an intense, albeit
brief, period of high snowfall rates within this band where rates
of 1-2 inches per hour are possible. The main limiting factor for
accumulation will be the warm surface temperatures in the
mid-30s. Therefore, the main message with this snow band will be
reduced visibilities in heavy snow and accumulating snow on
mainly grassy surfaces, though one cannot rule out some impacts
to roads for a short period.
.DISCUSSION...(This evening through Tuesday)
Issued at 237 PM CST Tue Dec 13 2022
- A complex winter storm will linger through late week, with the
highest confidence for wintry impacts, including difficult
travel, north of I-94 from multiple rounds of precipitation
tonight through early Thursday. Some updates to precip
types/amounts remain likely as this system passes.
- Much below average temperatures are increasingly likely late
this week into next week.
Tonight-Friday: Slow-moving, complex winter storm continues
A deep, nearly vertically stacked low pressure system continues to
spin across the central plains this afternoon. Strong, gusty winds
up to 35 to 45 mph will persist into tonight with a tightened
pressure gradient and low-level jet just off the surface.
Anomalous deep moisture transport (precipitable water exceeding
0.80") will continue to feed north ahead of the low with rain
spreading north and east late this afternoon and tonight. Some
transient mixed precip could occur south of I-94 but the primary
area of concern remains areas north of I-94 where surface temps will
likely hover near freezing for a longer period of time. Some
differences in the strength of the warm nose aloft exist among
models, impacting whether precip tonight is more liquid vs
mixed/snow. The greatest risk for freezing rain will occur overnight
into early Wednesday, with impacts highly dependent on surface
temps/dew points. The NBMv4.1 has continued to increase with 60%
probabilities of at least 1/10" of ice at Medford, WI and lower
probabilities around 20% for 1/4" inch. If the temps are slightly
warmer, the icing threat would be reduced considerably. Likewise,
if the thermal profile aloft is a bit cooler, more snow/mixed
precip would be likely. Given the marginal temps, expect icing
impacts to be most noticeable for elevated surfaces. As warmer air
gets wrapped northward on Wednesday, some drizzle may persist
behind the main precip band, with a transition to rain/snow for
north central Wisconsin.
Precip amounts have trended upwards on Wednesday night across
central/northern Wisconsin as an embedded shortwave rotates
through the broader trough and moisture continues to wrap
northward around the low. Depending on the placement of this band,
several inches of snow could occur within a deformation band,
especially across north-central Wisconsin. The HREF indicates
potential for snow rates exceeding 1"/hr in the band Wednesday
night, mainly just to the east in northeast Wisconsin. So,
potential exists for higher amounts where this band develops.
Given the prolonged nature of this event with rounds of precip
spread across multiple days, elected to convert the Winter Storm
Watch for Clark/Taylor counties into a longer duration advisory
through Thursday morning. That said, will have to monitor the
potential for heavier snow Wednesday night and impacts
tonight/early Wednesday from the mixed precip.
High latitude blocking will slow the progression of the large scale
trough keeping the region in cyclonic flow aloft with snow
showers/flurries at times into the weekend and some relatively
light accumulations possible.
This Weekend into Next Week: Much Colder
A transition to colder weather is likely heading through the weekend
and especially into next week as the slow-moving low finally moves
east. There is strong ensemble agreement for much below average
temps into next week with highs in the single digits/teens by early
to middle portions of next week and potential for subzero low temps.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 529 PM CST Tue Dec 13 2022
Main taf concerns are IFR/LIFR conditions at both taf sites through
the taf period. Low pressure over the Northern Plains States will
continue to wrap lower ceilings and precipitation across the area
tonight into Wednesday. Latest metars show MVFR conditions across
parts of southeast Minnesota...western Wisconsin and parts of
northeast Iowa with lower ceilings/IFR conditions over central
Iowa/southwest Minnesota. Ceilings will lower into IFR at both
taf sites this evening and to LIFR at RST after 09z. Precipitation
at both taf sites should remain all rain through the taf period.
However a very brief period of wintry mix...less than an
hour...will be possible early in the taf period and any longer
duration of wintry mix should be confined over north central
WI...Winter Weather Advisory until 9 AM CST Thursday for WIZ017-029.
Winter Weather Advisory until 6 AM CST Wednesday for WIZ034.
MN...Wind Advisory until 9 PM CST this evening for MNZ086-087-094-095.
IA...Wind Advisory until 9 PM CST this evening for IAZ008>010-018-019-
Area Forecast Discussion
National Weather Service Green Bay WI
931 PM CST Tue Dec 13 2022
New Information added to update section
Issued at 931 PM CST Tue Dec 13 2022
Do not foresee making significant changes to the forecast and
headlines late this evening. Arcing band of precip continues to
swing northeast but is running into ample mid-level dry air based
on the 00z KGRB sounding. Precip has been most consistently
hitting the ground over central WI from Marshfield to Wautoma
where a wintry mix has occurred so far this evening. Some of the
stronger returns may provide light precip to the Fox Valley, but
they probably won`t be strong enough to induce the cooling (wet-
bulbing) effect on temps to freezing where icing could become an
Otherwise, thermal profiles are setting up for a freezing rain
event over central WI late tonight into Wednesday morning when
the steadier precip remains expected to arrive. The warm nose
aloft continues to surge to the northeast and across the state
based on the RAP analysis. Meanwhile, surface wetbulb temps have
cooled slightly over north- central and central WI where the
freezing line is just south of Wautoma and Wisconsin Rapids. The
freezing wetbulb temps may shift slightly north overnight based on
the latest trends, but probably not enough to alter forecast ice
The freezing rain will likely peak near the morning commute time
over central WI so motorists are urged to exercise caution on
their way to work in the morning.
.SHORT TERM...Tonight and Wednesday
Issued at 259 PM CST Tue Dec 13 2022
Winter weather headline changes are the main focus in the short-
Precipitation trends: have slowed down the northeast progression
of the precipitation a little bit from the previous forecast.
Freezing rain/ice accumulations: Slightly warmer temperatures in
Waushara County resulted in a a decrease in freezing rain/icing
there tonight. The greatest threat for freezing rain remains
focused over Marathon and the northern portions of Wood and
Portage counties, where a tenth to quarter inch of icing is
expected. However, light ice accumulations are still possible in
counties to the north and east of the original advisory.
Snow/accumulations: have lowered snow accums tonight into
Wednesday, due to mixed precipitation resulting from the warm
layer aloft and drying in the mid-levels on Wednesday. Expecting
less than an inch of snow tonight, and generally 1 to 2 inches
over NC/far NE WI on Wednesday. The heaviest snow is still
expected to occur Wednesday night as the band of heavy
precipitation and dynamic cooling wipes out any lingering warm
layer aloft in the evening.
Headline changes: slightly warmer temperatures in Waushara County
have resulted in a decreased threat for freezing rain tonight, so
the Winter Weather Advisory has been cancelled there. The advisory
has been expanded north and east to include Lincoln, Langlade,
Menominee, Shawano and Waupaca counties - most of this area should
see ice accums of less than a tenth of an inch. The expiration
time for the entire advisory area has been extended through midday
The Winter Storm Watch was maintained for all previous counties
in NC/far NE, but the start time was delayed until noon. The Watch
for Door County was not changed, though snow amounts were lowered
a little bit. The Watch was expanded farther south into Waupaca,
Outagamie, Brown and Kewaunee counties to account for higher
snowfall totals of 4 to 6 inches. As mentioned earlier, the warm
layer is expected to erode over our southern counties in the mid
to late Wednesday evening, leading to the potential for a brief
burst of heavy snow when the main band of precipitation moves
.LONG TERM...Wednesday Night Through Tuesday
Issued at 259 PM CST Tue Dec 13 2022
The main concern for the extended period will be the resolution
of the wintry system for the end of the work week into the
weekend. A secondary concern will be arrival of a round of much
colder air behind the system for the end of the weekend into early
Precipitation will be ongoing Wednesday evening, with snow to the
north and rain across central to east-central Wisconsin.
Precipitation will transition to all snow rapidly for the early
evening, with mostly snow expected after midnight. Models have
generally trended higher with qpf, especially in the hours after
midnight through mid Thursday morning. Also suspect the models
haven`t fully captured the potential wet bulbing in the early
overnight, so brought temperatures down a a little earlier in the
evening, which will also increase snow totals. The main result of
these changes is an increase of snow total along the Highway 29
corridor. The bulk of the snow will be realized after midnight
through Thursday morning, which most of northeast Wisconsin seeing
4 to 6 inches in this 12 hour timeframe, but depending on how
quickly the p-type transition is realized, these snow totals could
still shift an inch or so in either direction.
After the bulk of the precipitation moves through Thursday
morning, the low pressure system will continue its slow journey
across the region through Saturday afternoon, with on and off
scattered showers likely across the region through the period.
This may mix into rain at times during the afternoons. Dry
conditions then finally return by Saturday afternoon into Sunday.
Finally, much colder air will follow behind this system for the
end of the weekend into next week. High temperatures are expected
to drop into the teens by Monday, with overnight low temperatures
likely below zero.
.AVIATION...for 00Z TAF Issuance
Issued at 522 PM CST Tue Dec 13 2022
A large, complex storm system will generally bring poor flying
conditions to the region thru 00z Thursday. Mainly MVFR/IFR
flight conditions are expected through the TAF period. VFR
conditions are possible for a several hour period across northeast
WI late tonight into Wednesday morning. Otherwise, a band of
precip consisting of a wintry mix will mainly impact central WI
tonight into early Wednesday. Icing is possible from late tonight
through midday Wednesday at AUW/CWA.
Precip will spread across the rest of the region on Wednesday
bringing a wintry mix to areas northwest of the Fox Valley, and
mainly rain to the Fox Valley and Lakeshore areas. 1-3 inches of
snow will be possible across areas north of HWY 29 through the day
Strong southeast winds of 15 to 25 knots with gusts to 25 to 35
kts are anticipated late tonight through Wednesday afternoon.
Significant LLWS will also overspread the region from west to east
tonight into Wednesday morning.
Winter Storm Watch from Wednesday afternoon through Thursday
morning for WIZ005-010>013-018>021-030-031-035-036-073-074.
Winter Weather Advisory until noon CST Wednesday for WIZ018>020-
Winter Storm Watch from Wednesday evening through Thursday
morning for WIZ022-037>040.
Area Forecast Discussion
National Weather Service Jacksonville FL
832 PM EST Tue Dec 13 2022
Issued at 830 PM EST Tue Dec 13 2022
The current forecast generally on track with considerable cloudiness
over the area as overrunning/isentropic ascent exists aloft and a
weak inverted trough continues off the east coast. Not much in
the way of any showers along the trough in our forecast area, but
showers further south over south and central Florida will head into
our area early Wednesday morning as the trough and a warm front
lift northward ahead of an approaching cold front, which is still
well to our west. For the update, just made minor adjustments to
the min temps, but temps for rest of tonight will remain fairly
steady or drop a few degrees from this evening. Based on latest
guidance and a few runs of the HRRR model, have expanded 20-30
percent shower chances a bit along the coastal counties later
tonight and continued into Wednesday morning and early aftn.
Northeast surface winds will relax a bit tonight, and some patchy
fog possible further inland in northeast Florida as the winds
relax there at or below 5 mph.
The marine forecast was not changed much with seas nearshore
above some of the guidance near 5-7 ft. We have also trended
dominate wave periods toward wind waves of 6 seconds or so
initially, and then as winds relax in next 6-12 hours, background
easterly swells of about 14-15 seconds will be dominate.
.NEAR TERM [Through Wednesday]...
Light coastal showers will continue on into the afternoon and
then ceasing overnight as light showers enter into southeast
Georgia from out of the west with the prevailing flow shifting
about to become more uniform out of the southwest. Breezy surface
winds will continue to be out of the northeast-east and becoming
more mild over inland areas overnight with cloud cover becoming
more dense by morning. Coastal areas will still experience
slightly gusty southeasterly winds on into Wednesday. High
temperatures for today will reach into the 60s and 70s, with
cooler temps occurring over southeast Georgia. Overnight low
temperatures will drop down into the 50s over most inland areas
and in the lower 60s for coastal areas in northeast Florida.
.SHORT TERM [Wednesday Night Through Thursday Night]...
Showers and storms will be moving through the region late
Wednesday night and through much of Thursday as a trough ahead of
an advancing cold front crosses over the southeastern states from
out of the west. Severe thunderstorms are possible ahead of the
fropa, with supercells and a potential for tornadic development.
Most likely threat in association with these storms will be
damaging wind gusts. Cold dry air will begin to build in behind
the front on Thursday night, bringing dry weather and clearing
skies over the region by Friday. Temperatures during this period
will be above the seasonal average with temps rising up into the
upper 70s. Overnight lows for midweek will drop down into the 40s
following the passage of the frontal boundary on Thursday.
.LONG TERM [Friday Through Tuesday]...
Cold air and northwesterly winds will settle in over the region
through the weekend with potential for frost formation and a
possible freeze Saturday night into Sunday morning. Potential for
showers over the southernmost portion of the forecast area, from
along the southern edge of the frontal boundary up into areas
along the I-10 corridor as it lifts slightly northward before
reinforcing southward before early Monday. Temperatures will drop
over the course of the weekend with temps dropping to below the
seasonal average with temps starting to rise again on Monday.
Issued at 647 PM EST Tue Dec 13 2022
A mix of VFR and MVFR ceilings are persisting over the area with
the MVFR currently existing for JAX, CRG, and VQQ. There may be
some ceiling improvement overnight, but periods of MVFR ceilings
may return for the early morning hours. A few showers may also
develop later tonight and into Wednesday as a warm front lifts
northward, with showers mainly affecting SGJ, CRG, and SSI. A low
end chance of IFR ceilings for GNV around 10Z-14Z, but not confident
in showing this chance at this time. Improving ceilings to VFR for
all TAFs on Wednesday after about 15Z-18Z, except for SSI where
we kept MVFR in place. Northeast sfc winds about 8-13 kt at 00Z
expected to weaken overnight and slowly turn more east-northeast,
then east to southeast 7-11 kt by mid to late day Wednesday.
The coastal trough will continue to linger over the local
Atlantic waters today then begin to lift northward as a warm front
late tonight into Wednesday in advance of an approaching cold
front. A pre-frontal line of potentially strong thunderstorms
will cross the waters early Thursday morning trailed by the cold
front passage Thursday evening. Elevated combined seas will
continue Small Craft Advisory conditions over portions of the
local waters through late Thursday. High pressure will extend
across the Gulf Coast region Friday into Saturday as local winds
and combined seas decrease below advisory levels.
.PRELIMINARY POINT TEMPS/POPS...
AMG 52 73 64 72 / 10 10 80 90
SSI 57 71 64 75 / 20 20 70 100
JAX 58 76 64 75 / 20 20 70 90
SGJ 63 76 64 75 / 30 30 50 90
GNV 59 79 63 75 / 0 0 70 90
OCF 60 79 65 76 / 10 0 70 90
FL...High Rip Current Risk through Wednesday evening for FLZ124-125-
GA...High Rip Current Risk through Wednesday evening for GAZ154-166.
AM...Small Craft Advisory until 4 AM EST Wednesday for AMZ450-452-454.
Small Craft Advisory until 1 AM EST Friday for AMZ470-472-474.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
836 PM CST Tue Dec 13 2022
Issued at 835 PM CST Tue Dec 13 2022
Widespread rainfall has moved into the northeastern quadrant of
Illinois this evening, with the leading edge reaching the
lakeshore around 8pm. This swath of steady rainfall will continue
lifting to the nne overnight, with a break in precip expected to
begin over the next hour to two from the sw CWA into the central
CWA. However, still appears another wave of precip will develop
from what is beginning to appear across eastern Missouri. Rainfall
is forecast to prevail through the morning commute, then taper
off to scattered showers tomorrow before redevelopment of
widespread rainfall returns tomorrow night.
Issued at 236 PM CST Tue Dec 13 2022
The northern extent of the approaching rainfall is beginning to
graze the far western CWA as of 2PM. On a north-northeastward track,
we`ll have to wait until later this afternoon or even early this
evening before this stuff really starts to fill in across the area.
While there are still embedded pockets of moderate rainfall, the
overall intensity of the rainfall appears to be on a downward trend
with areas of 40+ dBZ becoming fewer and further between on radar.
Additionally, all of the lightning that this system was producing in
Missouri earlier today got left behind as the system progressed
northward. The reason being lesser instability aloft as you move
toward the CWA. Speaking of, instability is also on a downward trend
for this evening and overnight. Whereas the RAP and HRRR were
displaying upwards of 200 J/kg of CAPE near 600mb over parts of the
southern CWA tonight, that number has now dropped closer to about 50-
100 joules. Now the potential for widespread heavy rain is looking
less likely and the thunder potential, slim to none. Nonetheless,
with still some instability in place, deep layer saturation, and
help from a robust low level jet, a very healthy rainfall can still
be expected this evening and overnight. High-res guidance is showing
anywhere from around a half an inch to an inch of QPF through
Most of us will wake up to rain continuing tomorrow morning before
it begins its departure to the northeast through the latter part of
the morning into the afternoon. Some brief, low level dry air
advection will put us in a lull for the widespread rainfall tomorrow
afternoon with some scattered showers probably still in the area.
Tomorrow evening, a second surge of rainfall is expected to move in
from the south with the passing of the storm`s occluded front and
plenty of upper forcing as the mid-upper level jet max moves over
the area. Timing in the onset of this second surge is fairly
uncertain, though a few pieces of guidance suggest we could see it
move in as early as late tomorrow afternoon. Better chances arrive
in the evening, so please refer to the long-term discussion below
for more details on that.
Meanwhile, winds are beginning to ramp up this afternoon. Increasing
winds aloft are not contributing much to gusts down at the surface
with the strong inversion in place. Our mixing for the time being is
essentially capped at around 925mb. This won`t change much as we
head into the evening and overnight. However, winds will continue to
build with the surface gradient flow strengthening as the low
pressure center inches closer and winds through the shallow mixed
layer also increasing. Very late tonight into tomorrow morning will
see the strongest winds with gusts to near 40 mph. Breezy conditions
will continue tomorrow, though winds will gradually subside through
the day. Finally, temperatures will be cooling off briefly this
evening before steadily warming overnight as we move into the
storm`s warm sector. We will drop as low as the middle 30s this
evening and will be back into the lower 40s by sunrise tomorrow.
Afternoon highs tomorrow will climb into the upper 40s to near 50
degrees despite the rain and cloud cover. Unfortunately, this is the
top of the hill before we begin a steady decline into temperatures
more appropriate for winter for the latter half of the week.
Issued at 236 PM CST Tue Dec 13 2022
Wednesday night through Tuesday...
The key weather messages in the long term are:
* Increasing signal for a second round of cold, and at times
heavy, rainfall Wednesday night
* Brief potential for snow to mix in north of I-90 late Wednesday
night/early Thursday morning
* Turning colder and blustery through the end of the week with
intermittent chances for scattered snow showers.
While this looked like an outlier scenario a few days ago,
forecast guidance continues to more strongly suggest a second,
arguably more vigorous disturbance, blasting northward along the
southeastern flanks of our sprawling upper low on Wednesday night.
An attendant 125 kt jet streak will deliver intense upper
divergence as a core of 120+ m/12 hr height falls spreads across
central and northern Illinois. PWAT values will be hanging out
near/just under an inch, which is still near the 90th percentile
for this time of year, and given the impressive dynamics at play,
confident in widespread rainfall developing rapidly through the
evening and overnight, and some of this rain will likely be heavy.
Would not be surprised to see swaths of additional amounts
nearing two inches through Wednesday night (this would be on top
of what falls tonight and Wednesday). Contemplated adding a slight
chance of thunder to the Wednesday night grids as well with some
signs of instability lingering upstairs, but have refrained for
the time being. Given the increased QPF amounts, we`ll need to
keep an eye on area rivers, with some potential for modest river
rises and some instances of mainly minor flooding heading into
The other development today is an increasing signal for dynamic
cooling to play a more central role in possibly transitioning
precipitation over to a rain/snow mix or even briefly all snow
late Wednesday night/early Thursday morning. Latest GFS and ECMWF
are actually pretty close from a thermal profile and forcing
standpoint. Intense forcing for ascent acting upon a plume of
impressively steep lapse rates (600-400 mb) results in a column
that dynamically cools towards and below freezing between roughly
midnight and 5 AM, mainly north and east of I-90 or thereabouts.
Verbatim, forecast soundings would support a rain/snow mix (ECMWF)
or even all snow (GFS) before the dryslot arrives and rapidly
transitions any lingering precipitation to a light non-freezing
drizzle or showers. For this forecast package, think it`s
reasonable to add a bit more snow to the grids in this area. That
said, surface temperatures will be very marginal, generally in the
mid 30s, which will blunt the potential for travel impacts, and
10:1 and Kuchera snow maps are likely way overdone on any snow
accumulations. Have added some light accums in our far northeast,
but presently not looking at this being a big deal. Something to
keep an eye on though given the magnitude of instability and
A colder airmass will generally just "spill" into the region (as
opposed to a sharp temperature drop) as the cold front swings
through on Thursday. Looks like we`ll get a brief break in
activity through the morning, but looking for additional precip to
develop during the afternoon and evening. While surface
temperatures will be above freezing, wetbulb zero heights will be
close enough to the surface to support snow showers. By later in
the evening and overnight, things look to saturate enough to
support some more robust snow showers, and this potential will
continue through Friday and Friday evening. The pattern through
the end of the week (and even into Saturday) will be supportive of
embedded heavier bursts of snow and scattered coatings (perhaps
locally over an inch). Have beefed up snow shower wording a bit
into Saturday. Otherwise, breezy and colder conditions will
prevail into the start of next week.
For the 00Z TAFs...
Primary aviation concerns through the next 24 to 30 hours
* Breezy east to southeast winds with gusts at or above 30kt
overnight and 20 to 25 kt throughout the day tomorrow.
* Lowering cigs and visibilities through the TAF period including
IFR and LIFR at times especially after sunrise tomorrow
* Periods of showers through the next 24 to 30 hours
* Low (<15%) chance that snow mixes with rain at ORD after 06Z
Currently, a large low pressure system is centered in southwestern
Nebraska with arcs of showers extending eastward and into the
western Great Lakes. As the low gradually drifts eastward tonight,
showers will expand in coverage and move over the terminals. At
the same time, east to southeasterly winds will increase in
magnitude with gusts of 25 to 35 kt becoming common, highest at
RFD. Cigs will gradually lower throughout the night with VFR
transitioning to MVFR sometime in the 05-07Z timeframe, and MVFR
to IFR toward daybreak. Visibility will also gradually lower with
prevailing values in the 3 to 5 mile range by daybreak owing to
pockets of drizzle and mist.
Much of the same is expected from sunrise tomorrow onward with
reduced cigs, visbys, and on-and-off showers. East to
southeasterly winds will remain breezy, but gradually lower in
magnitude from late morning to early afternoon. Toward evening, a
secondary low pressure system is expected to rapidly develop in
southern Indiana leading to a "kink" in the low-level pressure
field over northern Illinois and northwestern Indiana. As a
result, low-level winds should decrease in magnitude markedly
during the evening allowing for cigs and visbys to deteriorate
(potentially as low as 300-400 feet and 1-2SM, respectively), just
as an area of steady rain develops overhead. Visibility may lower
further as rain intensity picks up after 00Z.
Finally, there appears to be a low (<15%) but growing chance that
snow mixes in with rain after 06Z Thursday at ORD. With marginal
surface temperatures and a "wet" start, the main threat with snow
may end up further reducing visibility rather than sticking on
runways. In addition, a lightning strike cannot be ruled out over
the next 24 to 30 hours, though the chance of such occurring in
the vicinity of any given terminal appears less than 5%.
Issued at 236 PM CST Tue Dec 13 2022
...Gale Warning in effect for the southern Lake Michigan nearshore
Tuesday evening through Wednesday afternoon...
An approaching storm system is building winds up through the day and
will continue to do so this evening and tonight. Gales are expected
to arrive by mid-evening with gusts upwards of 45 kt anticipated
very late tonight into early Wednesday morning. Gales will persist
into the afternoon, though winds will gradually subside throughout
the day. Occasional waves to 18 ft are expected along the
Illinois nearshore, particularly in zones LM740 and LM741. Indiana
nearshore zones will see occasional waves to near 8 ft.
LM...Gale Warning...nearshore waters until 3 PM Wednesday.
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Area Forecast Discussion
National Weather Service Nashville TN
738 PM CST Tue Dec 13 2022
Issued at 731 PM CST Tue Dec 13 2022
Already we are seeing echoes enter West Tennessee as a strong cold
front bears down on the Mississippi Valley this evening. The 00Z
sounding from OHX shows considerable moistening of the column in
the past 24 hrs., but still no instability. Surface pressure
gradient has already tightened up considerably in advance of the
approaching frontal boundary. The most recent HRRR starts bringing
showers across the Tennessee River by 04Z and to the Cumberland
Plateau by 10Z. Most of the mid state is in for several hours of
rain later tonight and tomorrow, as multiple waves develop before
a surface low moves directly across the mid state tomorrow
evening. At this time, no forecast changes are planned as the
current forecast seems to have a good handle on the progression of
(This afternoon through Thursday Night)
Issued at 212 PM CST Tue Dec 13 2022
Primary surface low remains stacked across the central Plains this
afternoon. Trailing cold front extends southward through the
Arklatex region. Showers are located as far east as eastern AR.
Look for rainfall to move in tonight into our western zones by late
evening and then overspread the area. 850 mb jet will reach the area
late tonight. This feature tends to focus more on far southwestern
middle TN where differential speed convergence along the jet is
centered most. The stronger forcing down there will set the stage
for potential flooding by Wednesday afternoon and evening when the
second round of stronger forcing moves through, compliments of
the primary frontal boundary. As far as tstm potential goes, we
are picking up some elevated instability with 850 mb showalter
values close to zero. Total precip amounts look like 1 to 2 inches
except in our southwest where around 3 inches looks possible
through Wednesday night. For this reason we will go ahead and
hoist a flood watch for our far southwest, including Wayne,
Lawrence and Giles counties. The watch will be in effect from 18Z
Wednesday until 12Z Thursday morning. Note that WPC and Hrrr data
has trended downward over the last several runs. Hence, the reason
for just a small watch inclusion area. Otherwise, look for
clearing skies on Thursday with temperatures returning to more
(Friday through next Tuesday)
Issued at 212 PM CST Tue Dec 13 2022
In the extended forecast, looks like a benign and seasonably cold
pattern on Friday and through the weekend. Next week sometime, some
arctic air will be poised to plunge southward, perhaps. No
consequential storm systems are indicated at this time for our
For the extended temperatures, looks like lows in the 20s and highs
in the 40s.
Issued at 559 PM CST Tue Dec 13 2022
CKV/BNA/MQY/CSV...Several admendments possible, especially
14/06Z-14/24Z per fluctuations in ceilings, vsby, and impacts
of showers at and in vicinity of terminals. Expect surface winds
especially after 14/10Z to gusts up to 25kts with a strong low
level atmospheric pressure gradient supporting low level wind
shear 40-45kts after 14/10Z. Expecting surface winds to prevail
SE-S with sustained winds around 10kts. Can not rule out potential
of isolated thunderstorms at terminals or in vicinity, but
potential is only marginal and do not believe as of this time a
FM prevailing group or vicinity thunderstorm remark warranted.
.PRELIMINARY POINT TEMPS/POPS...
Nashville 52 61 41 53 / 80 100 100 0
Clarksville 52 61 38 50 / 100 100 100 0
Crossville 44 53 41 49 / 60 100 100 0
Columbia 53 60 40 53 / 80 100 100 0
Cookeville 48 56 42 50 / 70 100 100 0
Jamestown 44 54 42 48 / 70 100 100 0
Lawrenceburg 53 60 40 53 / 80 100 100 0
Murfreesboro 51 58 41 53 / 70 100 100 0
Waverly 52 60 37 50 / 100 100 100 0
Flood Watch from Wednesday afternoon through Wednesday evening
Area Forecast Discussion
National Weather Service Blacksburg VA
909 PM EST Tue Dec 13 2022
A large low pressure system over the central United States will
push across the east on Wednesday and Thursday, bringing rain
for the Mid Atlantic and Carolinas and also winter weather north
of I-64. Behind this system colder and windy conditions are
expected through the weekend. High pressure and dry weather
build in for Monday.
.NEAR TERM /THROUGH WEDNESDAY/...
As of 910 PM EST Tuesday...
Some of the lower clouds scattered out towards Roanoke this
evening as mid and high clouds increased across the area.
Elsewhere, stratus remains as moisture is locked under a low
level inversion. Current temperature trends indicate maybe a
wider valley/ridge split in temperatures than previously
expected, so have adjusted overnight lows some. Timing of
precipitation beginning in the west around 9-10 AM still looks
As of 620 PM EST Tuesday...
Not many changes to the overnight forecast...
Low clouds stuck under inversion may be slow to clear if at all
across the New River Valley into the NC mtns. High clouds
increasing as well, so look for mostly cloudy to overcast skies
overnight. Temperatures drop fast this evening before clouds
move in, so kept lows in the mid 20s to lower 30s.
Chance of rain arriving by afternoon...
Visible satellite images indicating some erosion and thin of low
clouds. Expect some additional breaks for the next couple of
hours. The clouds are thin but what doesn`t erode will be around
for much of the evening. Otherwise coverage of high clouds will
increase and cloud heights will lower overnight.
At the surface Virginia and North Carolina will remain
entrenched in a deep surface based wedge of cold air.
Increasing southwest flow over this layer of colder air will
provide strong warm air advection and aide in saturating the air
mass from the top down. Will have the probability for light
rain starting in the mountains around 10Z/5AM.
Similar to the past several days,clouds will limit the spread
between high and low temperatures. Will lean toward HRRR and
GLAMP guidance for hourly temperatures.
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 200 PM EST Tuesday...
Confidence is high for rain Thursday, with a period of freezing
rain for the higher elevations mainly north of the Roanoke
Valley Thursday morning.
A deep upper level low (the same one responsible for a northern
Plains winter storm) will be in place over the Upper Midwest at
the start of this period of the forecast. Shortwave energy
rounding the base of this trough will likely induce coastal low
development by for the Mid-Atlantic, with moderate to heavy rain
for the southern Appalachians, and mixed wintry precip farther
north. For our forecast area cold air is lacking for much in the
way of wintry precip. There will likely be a period of time
early Thursday when temperatures flirt with freezing for the
higher elevations...mainly north of the Roanoke Valley, where
freezing rain would be of concern, but overall just expecting a
cold rain which may be heavy at times Thursday morning.
While any small changes in the temperatures could shift the
areal coverage of freezing rain for Thursday morning, think
the models have a good grasp on warm nose aloft which should
limit overall threat for anything extreme for our forecast area.
With model temperatures near +5 deg C it will be hard to
sustain temperatures below freezing for any length of time. The
ground was not froze going into this event, so if there is any
icing it should be limited to elevated objects. The best chance
of icing will be along the Interstate 64 corridor where a tenth
of an inch of ice would be possible on elevated objects, e.g.
trees and powerlines. Some freezing rain could stretch southward
along the higher elevations surrounding the New and Roanoke
River valleys, but icing amounts will likely be less than a
tenth of an inch there.
The rain is expected to come to an end from west to east
Thursday afternoon as the storm evolves and moves up the Mid-
Atlantic Coast. Overall QPF (rain totals) for the event are
forecast to average between 1 and 2 inches. Attm this does not
appear that it will result in any flooding, since the event will
be of long duration, but do expect modest rises on area rivers
given a mean of 1.50 inches of rain.
For Thursday night into Friday, a cold front will cross the
region bringing the winds around to the west associated with
falling temperatures and breezy conditions. Drier air will begin
to work into the region scouring some of the cloud cover. Not
impressed with the trajectories for mountain snow showers until
later in the weekend. Bottom line, not seeing anything extreme
or hazard/headline worthy for Friday.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 200 PM EST Tuesday...
Confidence is high for gusty winds and colder temperatures this
Broad upper level trough of low pressure over eastern North
America is forecast to persist through the weekend...the
forecast area remaining in mainly dry cold west-northwest flow.
There is a jet streak that passes south of the area Saturday
which may result in a period of mid/upper level clouds, but with
no precip. For Sunday, the flow favors more of a northwesterly
flavor which may produce more in the way of low level upslope
clouds for the mountains, but little or none east of the Blue
Ridge. Precip from these clouds would likely be in the form of
flurries. Model soundings for BLF/LWB/TNB suggest moisture will
be shallow, moisture depth 5kft or less, so not expecting much
in the way of measurable precipitation.
After the weekend models diverge with respect to details, but
overall do not see any extremes. For now keeping things dry with
temperatures moderating slightly for mid week.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
As of 615 PM EST Tuesday...
High confidence in mainly VFR, though concerned lower cigs may
linger longer at BCB through this evening, but trending toward
it scattering out with high clouds increasing.
Still looking at delayed timing of precip til midday to early
afternoon in the mountains reaching perhaps DAN/LYH by end of
the taf period. At the moment not seeing any ptype issues at the
terminals. Looking for VFR through most of the period but
lowering to MVFR to possibly IFR at BLF/LWB/BCB by the end of
the taf valid period.
Average confidence in ceilings,visibilities, wind and arrival
time of rain.
Extended Aviation Discussion...
A low-level wind shear will increase Wednesday evening as a
large storm system approaches. Rain, along with MVFR conditions
will spread from west to east across Virginia and North Carolina
Wednesday night. Freezing rain is expected north of I-64 late
Wednesday night into Thursday morning.
Scattered MVFR snow showers may be possible Friday in the
mountains. Gusty wind is also expected in the mountains Friday.
MVFR clouds will linger in the western upslope areas of the
central Appalachians through Sunday. Ceilings will be VFR east
of the Blue Ridge.
Drier air will arrive for Monday and wind speeds will diminish
so VFR conditions are expected.