Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/31/20
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
516 PM CST Wed Dec 30 2020
Issued at 512 PM CST Wed Dec 30 2020
Adjusted sky grids with a lean toward the HRRR given the latest
trends on satellite with the stratus. Otherwise, no major changes
are planned to the current forecast.
.SHORT TERM...(This Evening through Thursday Night)
Issued at 314 PM CST Wed Dec 30 2020
We`ve seen a gradual eroding of a broken stratus deck from west to
east through the day, and that trend should continue through tonight
leading to mostly clear skies. While winds have been gusting upwards
of 35 mph throughout the day across the Prairie Coteau, they will be
diminishing this evening as a sfc high pressure axis continues
eastward. Given the favorable conditions and fresh snow pack, low
temperatures have been dropped to the lower end of guidance with
single digits possible for much of the area east of the Missouri
River. While not in the forecast due to low confidence, fog could
develop tonight in favorable areas (limited to no snow melt today
has contributed little to low-level moisture).
Thursday begins with a pocket of elevated southwest winds aloft, and
so relatively minor downslope winds may develop on the leeward side
of the Prairie Coteau through the afternoon. Drifting of snow will
be possible therefore as well during this time. Light breezes and
mostly sunny skies are expected for the rest of the area, as a warm
front lifts northeast through the day. High temperatures will be
held down some by the snow cover, but will still be above average in
the mid 20s to mid 30s.
.LONG TERM...(Friday through Wednesday)
Issued at 314 PM CST Wed Dec 30 2020
The oft-split flow pattern continues to dominate with only
minor/weak upper trough passages Friday and Sunday mornings, with
little to latch onto for precipitation chances. These features will
aid in mixing however, and without any major cold intrusions we will
see mostly above normal temperatures (though our recent snow pack
may have some local impact). Nothing really else of note for the
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 512 PM CST Wed Dec 30 2020
MVFR stratus is expected to exit this evening. Will need to watch
for any fog development toward morning, but otherwise VFR
conditions and light winds will prevail.
Area Forecast Discussion
National Weather Service Caribou ME
918 PM EST Wed Dec 30 2020
Low pressure will track northwest of Maine overnight. A cold
front will cross the area Thursday morning. High pressure will
cross the region on Friday. Low pressure approaches later Friday
night then crosses the region on Saturday. High pressure will
build in on Sunday before another low pressure passes south of
the region on Monday.
.NEAR TERM /THROUGH THURSDAY/...
9:17 PM Update: Snow will continue to fill in across the area
from Bangor north this evening. Temperatures along the coast
have moderated significantly this evening with a 10 degree (F)
rise at Bar Harbor Airport in the past couple of hours. Most
areas along the coast are now in the upper 30s and lower 40s, so
just rain expected. Bangor is about the dividing line between
rain and snow with all snow expected in areas to the north of
Bangor. A quick hitting system with most of the precipitation to
wrap up by 12Z with the exception of Washington County. In the
wake of this system, a cold front will cross the region tomorrow
with snow showers a good bet across the north with the chance
of a heavier squall. The latest BTV snow squall parameter does
indicate a decent chance of squalls in the morning and early
afternoon across the far north.
Clouds will continue to lower and thicken this evening w/snow
arriving into the western areas and then spreading east through
the rest of the night. Warm front will be lifting ne tonight
w/some WAA noted. There is a strong mid level jetstreak of 55-60
kts as noted by the NAM and RAP as well some good llvl
convergence. These two factors should be enough to generate some
snow as the column moistens. Interesting enough, the high
resolution guidance including the RAP/NAM and HRRR show the
potential for some moderate snowfall across northern and western
areas later this evening, and then a second area of higher
QPF(snow) w/strong llvl convergence across the eastern side of
the CWA. Steady snow is expected to wind down to snow
showers/flurries Thursday morning as the best forcing will be
moving off to the east and warm front lifts into New Brunswick.
There is potential for up to 4 inches of snow across portions
of the northern including Northern Penobscot and SE Aroostook
County. Given the aforementioned setup, decided to go w/a Winter
Weather Advisory through Thursday morning for MEZ001>006 which
covers all of Aroostook County, Nrn Somerset and Nrn Penobscot
County. Further s, less snowfall but a decision was made to
boost snowfall totals by an inch given that the warmer air get
pinched further s than previously forecast. This again is well
shown by the NAM/RAP and HRRR guidance. Speaking of that warmer
air, temps will warm up overnight w/readings by morning in the
upper 20s to lower 30s. Downeast areas, especially the coast
will see temps warm into the mid/upper 30s and this will allow
for snow to rain to rain.
Thursday will see a pre-frontal trof ahead of the cold front to
slide across the region during the mid mrng hrs which will
spark some snow showers across the northern and western areas.
NAM soundings show some good shear of 35+ kts and some weak SB
CAPE(= 50 joules). Llvl lapse rates are forecast to steep into
late morning which would allow for some instability. The Snow
Squall Parameter from the RAP and NAM support the potential for
some stronger snow showers and possibly a squall. Followed the
midnight crew`s assessment of staying w/snow showers attm, but
if the trends continue then a beef up in the forecast pops may
be warranted. It will be rather windy w/sustained SW winds of
10-20 mph and gusts getting into the 35 mph range. This will
especially be the case across the northern 1/2 of the CWA which
could lead to some blowing snow and w/the snow shower and
perhaps a squall could lead to rapidly changing vsbys. Temps
will be falling during the afternoon as the cold front arrives
into the region.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
For Thursday night, cold air advection is forecast with high
pressure building. Expect some subzero readings in the North
Woods. Elsewhere, lows will be in the single digits north and
teens in the southern half of the area. Could have to go a bit
lower since the high is building so rapidly during the
night...increasing the chance of winds going calm. Fresh snow
cover will also help push lows downward. High pressure and
sunshine is forecast for Friday with highs just above seasonal
norms. Lows for Friday night will occur during the evening as
temps drop quickly...but will remain steady later in the night
as clouds increase ahead of Saturday`s storm. The Saturday storm
will feature a southern stream shortwave pulling out of the
Mississippi Valley and phasing with a fast-moving northern
stream shortwave over the Great Lakes region. Surface low in the
Great Lakes region will give way to a coastal low early Saturday
afternoon. The questions are where the secondary does form and
how fast...Gulf of Maine or along the Massachusetts coast. This
has implications for both rain vs snow and amounts. More models
favor the more southern track with the GFS as the northern
outlier with a more amplified shortwave. Used a model blend to
generate a more southern track than the GFS and pushed the
rain/snow line a bit further south than our last forecast. This
compromise track places the heavier potential banding from
southern Piscataquis County towards southern Aroostook and
northern Washington counties. This is where some low-end warning
criteria snow is possible. However, a more southern track could
drop the heavier snow band towards Bangor and Downeast...while
reducing amounts in northern zones. This storm will be a fast-mover
and will quickly exit the area Saturday evening.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Snow ends Saturday evening and high pressure builds quickly
during the night. There`s no significant cold air advection
behind the low pressure system. A steep low level inversion
appears likely as lows drop to the low teens north and upper
teens to lower 20s in the south half of the area. Couldn`t rule
out some patchy freezing fog given the moisture from Saturday`s
event. The high continues in place Sunday with above normal
temps. Things become interesting for later Sunday night into
Monday as a southern stream cut-off low kicks out of the lower
Mississippi Valley and propagates eastward. This time, phasing
with a northern stream shortwave is not so clearcut. Some
guidance has the cut-off harmlessly meandering out to sea south
of the area while the ECMWF has been more consistent in
generating a slow moving coastal storm. Since there`s very
little cold air in place, coastal areas would be more likely to
see rain. Have increased PoPs from our last package, but still
mostly in the chance range north of the coast. The slow moving
part could be a big concern as there will be plenty of moisture
available if the Euro verifies.
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
NEAR TERM: Mostly IFR overnight at the northern terminals in
snow...with IFR to low end MVFR at BGR/BHB in rain/snow, with
mainly just rain at BHB. LLWS will also be a concern late
tonight into Thursday morning w/a SW jetstreak of 40+ kts at
2000 ft. Sfc winds tonight will be out of the S at 10 mph.
For Thursday, S winds to go SW 10-10 mph w/gusts of 35 mph. Snow
will wind down to snow showers and flurries in the early morning
at the northern terminals. Conditions will improve to VFR, but
northern TAF sites especially n of KHUL could see MVFR and
possible IFR w/some enhanced snow showers and perhaps a squall.
Low vsbys and and some strong wind gusts could accompany this
NEAR TERM: A south wind has rapidly increased this evening with
near gale force gusts as of 9 pm. A llvL jet of 40 kts moving
over the waters later tonight has the potential to mix down to
sfc at 35+ kts. There is good alignment w/the winds from the
blyr through 925mbs. Seas will respond accordingly building from
3-5 ft to 8 to 11 ft by early Thu morning. Rain will moving in
For Thu, SW 25-30 kt w/gusts 35-40 kt will shift to the W and subside
to 15-20 kt by mid afternoon. There could be some gusts to 25
kt into late afternoon. Seas of 8-11 ft will be dropping back to
5-7 ft by late afternoon. Rain early in the morning.
SHORT TERM: SCA conditions will continue into Thursday night and
then return Saturday into Saturday night. There could be a few
gusts to gale strength later Saturday. The next SCA starts
Sunday night and continues into Tuesday morning. Gale force
winds will be possible...and probable if a Noreaster does
ME...Winter Weather Advisory until 8 AM EST Thursday for MEZ001>006.
MARINE...Gale Warning until 1 PM EST Thursday for ANZ050>052.
Area Forecast Discussion
National Weather Service State College PA
1030 PM EST Wed Dec 30 2020
A cold front will bring a band of light rain or mixed
precipitation to the region starting late today across the
Northwest Mountains, and occurring mainly as rain tonight
elsewhere across Central and southern PA. A light accumulation
of a coating to one inch of snow is possible across the
Allegheny Mountains later tonight.
High pressure then slides overhead for Thursday, making most of
the day and evening dry with slightly above normal temperatures.
Low pressure over the southern Plains will lift into the Great
Lakes. This will force a large shield of mixed precipitation to
overspread the entire state, likely holding off until Friday
morning. A period of freezing rain is likely on Friday (New
Year`s Day). The air will warm up slowly on Friday, turning the
wintry mix to plain rain from south to north for most of Central
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
* Winter Storm Watch issued for a large swath of Central PA
Friday into Friday night for potential significant
accumulation of ice from Freezing Rain.
Late evening discussion below.
Cold front well to the northwest, and temperatures not real
cold. Guidance temperatures not near freezing until later
across the northwest, thus pulled snow out of most of the
area prior to 06Z.
Early evening discussion below.
Minor adjustment so far as of 6 PM was to take out the snow
early this evening, as so far just rain. While dewpoints lower
to the east, the rain is still to the west. Thus still have a
mix of rain and snow across the northeast later this evening.
Will continue to monitor and adjust as needed.
Afternoon discussion below.
Low level warm advection ahead of a relatively weak cold front
has led temperatures climbing to several to 10 degrees above
normal this afternoon with the greatest departures occurring
over the northern and western mountains where temps topped out
Latest RAP and 12Z HREFv2 indicate a 4-7 hour period of mainly
rain late today and early tonight, followed by a 2-4 hour period
when temps cool off enough to change the rain to wet snow with a
coating to one inch possible in places like KJST, KFIG, KDUJ and
A gusty south to swrly breeze will remain through this evening
before decreasing and shifting to the west-northwest in the wake
of the Cfront late tonight.
Min temps early Thursday will vary from the upper 20s north to
mid 30s in the Lower Susq Valley.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
The cfront will slip south and east be off to the east early in
the morning, and cold advection will keep temps from rising more
than 5F from their early morning values.
The precip along and just in the wake of the cold front with
the front will settle south of the MD border very early in the
day and should stay there, leaving us with dry weather and slow
clearing with gradually lifting cloud bases.
Clouds will thin out to mainly cirrus or patchy altocu across
the south toward dusk.
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
No major changes to the longer term, some light precipitation
possible across the region late next week.
Timing of the event for later this week, slower today, than
yesterday. Detail listed below.
Surface high pressure will move overhead Thursday and much of
Thursday night bringing cold, dry air to much of central PA. The
high centered over the Hudson Valley for Friday will be a good
set up for cold air to drain down in from the NE and stay in
place for a prolonged period. Meanwhile, a deep low will move
from the Ohio Valley into the Great Lakes with WAA spreading
northward across the region Friday, setting the stage for a
significant ice event over central PA.
Models have slowed down on the onset of precip, and it looks
more likely that this will mainly be a Friday/Friday evening
event. With precip and clouds arriving later, this will also
give more time for radiational cooling to occur Thursday night
with lows dropping into the teens north to 20s south,
increasing the threat for frozen precip Friday. Although a brief
period of snow or sleet is possible at the onset of precip,
freezing rain will be the main threat as warmer air moves in
aloft over the cold air trapped at the surface.
WPC guidance and the NBM holds a significant (>0.25") accretion
of ZR over the Laurels and along the Allegheny Front with the
highest amounts over the ridge tops. Given the continued signals
for significant ZR, we hoisted a winter storm watch earlier
today for a large swath of the CWA.
Most places should see temps rise above freezing Friday evening,
but a few spots in the north may see temps linger near freezing
into early Saturday morning.
Behind the storm, Saturday looks mild across the CWA with highs
in the 40s and 50s. A coastal system on Sunday may lead to some
rain or snow for parts of the region, but heavy precip does not
look likely at this point. Generally dry weather is expected the
rest of next week.
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
At 03z, cigs have dropped to IFR at BFD in continuing light
rain. Lower cigs and light rain showers will continue to slowly
spread southeastward overnight as a cold front crosses the area.
Widespread LLWS conditions are anticipated through the early
overnight hours, as the surface flow slackens but a healthy
S/SW low-level jet increases just above the surface.
As colder air moves in, a changeover to light snow is expected
overnight across the western highlands /BFD and JST/ along with
IFR conds. Post-frontal low clouds (fuel-alternate/MVFR cigs),
along with scattered flurries are expected at AOO, UNV, and IPT
overnight. MDT and LNS could flirt with MVFR cigs overnight as
Improving conds are expected on Thursday, as the front
gradually sags south of the area. An active weather pattern
will continue through the weekend, with additional rounds of
precip expected on Friday and again Sunday.
Fri...Restrictions expected, with a wintry mix developing in
the morning and transitioning to rain.
Sat...Restrictions early with lingering low cigs. Gradual
improvement by aftn.
Sat night-Sun...Deteriorating conds, with light rain/snow
Mon...Lingering restrictions in -SHSN across western highlands.
Becoming VFR elsewhere.
Winter Storm Watch from Friday afternoon through late Friday
night for PAZ005-006-010>012-017>019-037-041-042-045-046-049-
Winter Storm Watch from Friday morning through Friday evening
details can be found in the long-term forecast discussion below.
.LONG TERM... /Issued 334 PM CST Wed Dec 30 2020/
/Thursday Night through Wednesday/
The upper level low and its ejection out of northern Mexico and
across Texas Thursday represents the primary uncertainty in the
forecast. The trend in some of the models (Canadian/RAP/HRRR)
today has been a slightly slower and subtle eastward shift of the
track of the cyclone across our area. Based on some current water
vapor analysis and a general 30dm NAM/GFS initialization error in
the La Paz & Mazatlan RAOBs, it raises some concerns that this
system still has the potential to veer off its forecast course.
Any slower or more eastward track increases the potential for more
wrap around snow impacting more of the CWA and for a longer time
period Thursday night.
Upper level troughs undergoing a shift from positive tilt to
negative often do produce forecasting errors, because in general,
the open wave will continue to drop equatorward until it reaches a
baroclinic zone (or cold front). When it reaches the baroclinic
zone it will strengthen, thereby distorting or "waving up" the
horizontal temperature gradient. As warm air wraps around the
northeast side and cold air dives southward on its backside the
upper low will gain a poleward motion. The important thing to
note about this process is that if the position of the cold front
is not forecast well, then those errors cascade into impacting the
ultimate track the upper low. In our current situation, the
models have been trending the position of the cold front farther
south - now showing it well into Mexico by late tonight - and the
surface baroclinic zone has shifted from a forecast yesterday of
Laredo to College Station to near the Texas coast. This makes
sense as shallow cold fronts in Texas tend to head farther south
than forecast, and the warm ocean waters will provide a natural
baroclinic zone where the surface low will likely wrap up.
Regardless of the exact track of the upper low, we expect
widespread rain across the area early Thursday evening, but the
atmosphere will be undergoing rapid changes as the low approaches
and strong dynamic forcing overspreads the region. The upper
level dry slot will first move northward and across the central
and eastern zones during the evening hours with the widespread
rain coming to an end. Very strong lift should cool atmospheric
thermal profiles with mid level lapse rates increasing to 7-8
degrees C/km (good enough for isolated thunderstorms). Generally
to the west of the I-35 corridor, this cooling will result in a
thermal column completely below freezing. The change over from
rain to snow will progress from the southwestern CWA northward
during the evening hours - essentially following where the forcing
is strongest ahead of the upper low. At some point across the
central CWA, the pre-existing thermal profile will be too warm
for dynamic cooling to get the column below freezing.
While uncertainty is high regarding the eastward extent of the
snow line, using the high res ensembles yields a reasonable
looking snow forecast provided that the track errors discussed
above don`t become too great. The western zones, generally along
and west of 281 will be the primary location for accumulating
snowfall. Snow is still forecast to mix in with the rain up to
about the I-35 corridor late Thursday evening and overnight
Friday morning. Right now we are forecasting 1-4" over the western
zones, but acknowledge that very favorable dynamics associated
with wrap-around precipitation events are in place. This could
yield high snowfall rates of 2+ inches per hour and maybe even a
stray rumble of thunder. Given the potential for more significant
snow, but still hesitant to explicitly forecast more than 4
inches due to higher uncertainty, we have included a winter storm
watch for Young, Stephens, and Eastland counties. Just to the
east, an advisory will be issued for Lampasas county north to Jack
county, and including Montague county. Later shifts can determine
if a winter storm warning may be needed for the watch area or if
an advisory will still suffice. The watch and advisory will start
at 6 am to cover the low potential for light freezing rain
Thursday, but it`s primarily for the evening and nighttime hours.
Just to the east of the advisory counties (including the DFW
Metro), some rain/snow mix should occur late, primarily associated
with the wrap around band after midnight. Precip intensity looks
like it will be lower here and surface temperatures should stay
above freezing so accumulations should be insignificant and pose
no travel issues in this region.
Precipitation will rapidly exit the CWA by sunrise but post
frontal clouds will hang around on Friday. Have gone with the
cloudier MOS guidance and kept high temperatures on the cooler
side of the envelope and only in the 40s. Clouds should finally
clear on Saturday with a second upper level trough moving through
the region. Fair and quiet weather is expected through Monday with
highs warming a bit each day and lows in the 20s and 30s. The
next upper system will bring more clouds and warmer temperatures
to the region Tuesday and Wednesday. A few showers are possible
mainly across the eastern and southeastern zones where moisture
MVFR prevails this evening at TAF sites, but expect CIGs to fall
to IFR later tonight as widespread RA continues to develop.
Visibility will likely fall to IFR as well, particularly within
heavier rainfall areas. There is a potential for intermittent LIFR
CIGs during the day Thursday, but uncertainty is too high to
mention in TAFs at this time. Gusty north winds will continue
through the end of the TAF period.
Just beyond the TAF period, RA may mix with or transition to SN
across North Texas including at Metroplex TAF sites. This
potential will need to be monitored closely, and a mention of
RASN or SN may be needed in later issuances. Right now, no
accumulating SN is expected in the Metroplex, which would keep
impacts to ground operations at a minimum.
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 36 44 35 45 33 / 80 100 90 0 0
Waco 39 46 35 49 31 / 100 100 50 0 0
Paris 38 46 38 45 32 / 90 100 90 5 0
Denton 33 44 32 44 28 / 70 100 90 5 0
McKinney 36 45 36 44 31 / 90 100 90 0 0
Dallas 38 47 38 46 34 / 90 100 90 0 0
Terrell 38 48 37 46 31 / 100 100 80 0 0
Corsicana 43 51 39 48 34 / 100 100 60 0 0
Temple 38 46 34 50 31 / 90 100 30 0 0
Mineral Wells 32 40 32 43 28 / 70 100 90 5 0
Flash Flood Watch through Thursday afternoon for TXZ094-095-
Winter Weather Advisory from 6 AM Thursday to 3 AM CST Friday
Winter Storm Watch from Thursday morning through late Thursday
night for TXZ100-115-129.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
520 PM CST Wed Dec 30 2020
.DISCUSSION...(This evening through Wednesday)
Issued at 236 PM CST Wed Dec 30 2020
The main issues for this forecast is for dense fog and freezing
fog potential Thursday night Friday morning and keeping an eye on
a winter storm with a track that seems to be far enough southeast
to essentially avoid impacts to our CWA.
For tonight, I decided to put a little patchy fog in for our
southeast NE areas for a couple of reasons. This seems to be a
place where there was at least a little more melting of snow cover
along the southern periphery of the newly fallen snow, but also
the timing of the surface high gives us the lightest wind in this
area as well. We may want to add points west if it looks like
enough melting and/or wind looks like it would be light enough.
The real issue for fog is for Thursday night and Friday morning as
there is more potential for snow melt during the day on Thursday.
Wind will have a north direction, but could be light enough to
allow fog to occur. It will be cold enough that freezing fog could
be an issue and make roadways slick. Still early though. I made a
distinction toward where there would be recent snow cover over
Nebraska, and little or none for Kansas. although there still was
some signal for fog from SREF and HRRR, it was not as strong.
For the winter system coming out of Mexico, the trends for
snow/ice tracks continue to generally nudge southeast from the
CWA. We clearly look cold enough to only have to worry about snow
on the northwest shield of precip, but considering that convection
to the south often nudges these tracks of precip farther south
than model forecasts, I would not be surprised if our entire CWA
misses out on this all together. Still kept low POPs in our
southeast CWA, southeast of the tri-cities, but I can see this
trending downward in future forecasts if trends continue with
both ensembles and operational runs. The RAP really nudges this
well southeast of the CWA, and I think it probably has the right
Some models are going for a double barrel solution where another
upper low follows quickly behind the one tracking through on
Friday, coming up on the weekend, but this low, if it develops as
some models have advertised, should be far enough southeast to not
be an issue for us.
Looks like we will be cool to seasonable into next week as
shortwave ridging tries to move in and we will get a little
melting, perhaps each day.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday)
Issued at 518 PM CST Wed Dec 30 2020
VFR conditions are expected to prevail through this period. There
is very low end chance for some patch fog early Thursday morning,
but this is expected to stay to the southeast of KGRI and KEAR.
Winds will be light, shifting to the south overnight into
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1100 PM EST Wed Dec 30 2020
Issued at 1100 PM EST WED DEC 30 2020
Updated grids to bring them in line with hourly surface obs.
Seeing an honest uptick in rain shower activity across the area
now as a surface cold front is just entering our area. Made
additional adjustments to PoPs for recent radar trends - generally
sped up the increase in poPs across the area. The surface
boundary appears to have made it through Mt. Sterling and Morehead
on its way east-southeast across the area this evening and may be
on JKL`s doorstep. Am taking a close look at the 0Z runs as
solutions come in, trying to determine if there is any threat for
a wintry mix in the north. Forecast soundings and guidance suggest
a solid drop in temperatures close to, or possibly to the
freezing mark by dawn north of I-64, 32-34. And southwesterly
winds aloft keep a deep layer (a few thousand ft) of warm air in
place. Thus, by the strictest of definitions, can not rule out a
period of freezing rain in the morning. Even the last several runs
of the HRRR suggest the possibility. But have to believe any
impacts would be nil with ground temperatures so far above the
freezing mark and subsurface temperatures even warmer. Not even
sure if any elevated or exposed surfaces would manage to get any
ice accumulations without temperatures getting below freezing, and
at this time there is nothing suggests that will happen. NBM 50th
percentile does take temperatures in the northernmost portions of
our forecast area down to the 32 degree mark, but considering
other factors that may be too cool. Other guidance suggests lows
bottoming out right at 33. But will keep an eye out in case some
last minute adjustments to the forecast package are required
should trends in updated solutions take us in that direction.
UPDATE Issued at 725 PM EST WED DEC 30 2020
Surface cold front has made it into far western Kentucky,
southeast Indiana and western Ohio. This feature will continue to
slide eastward through the evening, tracking through eastern
Kentucky roughly between 04-12Z. Rain showers will continue to
spread eastward, with more steady rainfall expected later tonight.
Steady rainfall will taper off to isolated showers for a period
of time Thursday afternoon and evening, but returning Thursday
night as another low pressure system pushes into the Midwest. Did
need to make some adjustments to PoPs for this evening, bringing
in activity a little sooner than originally forecasted based on
current radar trends. Otherwise only made some tweaks to the
hourly grids to bring them better in line with observations.
.SHORT TERM...(This evening through Thursday night)
Issued at 328 PM EST WED DEC 30 2020
Strong southerly flow has continued this afternoon, ahead of a
cold front pushing its way across the Ohio river valley this
afternoon. We have seen a few wind gusts touch 35 mph, but
overall, winds have remained just below lake wind advisory
thresholds. The gusty winds will continue through early evening,
before subsiding a bit as the strength of the mixing decreases.
Temperatures have warmed into the lower 60s in most areas. The
main focus for the short term is around the cold front as it
pushes into and across the area tonight.
Winds will shift a bit more southwesterly this evening, helping to
transport better moisture into east Kentucky. The front will then
push into central/northern Kentucky by late evening, with
widespread rain expected along the boundary. The shield of rain
will gradually shift south and east overnight, reaching far
southeast Kentucky by dawn on Thursday. Mild temperatures will
persist this evening, but should plummet pretty quickly as the
front pushes south and east overnight. By morning, many areas will
see temperatures sitting in the 30s with a persistent light rain.
There is substantial warm air off the surface, even in the north,
that will keep precipitation all liquid, essentially just leading
to a very cold rain.
The cold front will stall out along the VA/KY state line on
Thursday, with low clouds hanging on north of the boundary through
the day. While rain chances should gradually diminish from the
north early Thursday, rain chances in the south and east could
persist well into the afternoon. The cloudy weather and rain will
keep temperatures fairly steady through the day, many locations
likely not making it past 40.
By Thursday night, we will be watching s developing low pressure
system take shape across the plains with the stalled frontal
boundary eventually lifting back to the north as a warm front.
Southeast downslope flow should strengthen through the night with
rain chances likely at a lull through much of the night. However,
there is some weak diffluence aloft late (or almost 12z Friday),
that may provide some support aloft for increasing rain chances
prior to 12z. However, the forcing is weak and the southeast flow
is quite strong. Thus, this may be a situation where we struggle
to see measureable rainfall through 12z. The better chances may be
in our western zones, closer to the better forcing. Temperatures
may hold steady again overnight, and possibly increase late as the
front starts to move back north.
.LONG TERM...(Friday through Wednesday)
Issued at 432 PM EST WED DEC 30 2020
A mild and unsettled pattern will be in place through Saturday
night before quieter and cooler weather arrives for the first
half of the new week. The 12z model suite is generally in good
agreement agreement on the upper level pattern through Friday
night. A few differences emerge over the weekend; but, with
exception of the Canadian, agreement improves for the first half
of the new workweek. The upper level analysis starting 12z Friday
shows a stout ~590 dam high over the Bahamas with a ridge
extending NW to over the upper Mississippi Valley. Another
positively-tilted ridge extends from the California Coast to the
northern US Rockies. A col, stretching from Nebraska to Utah
connects the two ridges. To the south of the col, the first of two
upper level lows is spinning over eastern Oklahoma while a second
low is situated near the Arizona/New Mexico/Mexico borders. North
of the col, a northern stream trough is passing over the Northern
Plains. At the surface, ~1003 mb high pressure will be located
over/near Arkansas with a warm front draped across the Tennessee
Valley to the Carolina coast while the system`s cold front
extends southeastward toward the Central Gulf Coast.
The first upper low will skim along the northwest periphery of
the strong southeastern high on Friday before opening into the
northern stream trough passing the Great Lakes on Saturday. This
will cause the surface low to lift toward the Great Lakes before
weakening and transferring its energy to a coastal low near New
England. A strong and very mild (10-12C @850mb) southerly 50+ knot
850mb jet will send the system`s warm front surging northward
across the forecast area Friday morning. The trailing cold front
will push in from the west by Friday evening but will falter as is
crosses the Appalachians. As that first upper low fizzles, the
second upper level low will evolve into a deeper low over the
southern Plains before pivoting across the Ohio Valley and Great
Lakes ahead of a deepening trough. This trough will continue to
sharpen as it drops into the Southeast US and shunts the strong
high near the Bahamas to over the Greater Antilles. At the
surface, this second system will cause a weak, broad surface
trough to develop late Saturday near the Mid-Mississippi Valley
before consolidating into the a coastal low along the Carolina
Coast early Sunday morning. As this occurs, a sub 0C 850mb air
mass will arrive/develop along the back side of the system. As
this second system departs, flat upper level ridging builds
eastward to over the Ohio Valley Monday and Tuesday with attending
surface high pressure. Another trough approaches from the west
mid-week but models differ on the details.
In sensible terms, widespread rain showers are expected to lift
northward with the warm front Friday morning. Immediately
downwind of the Cumberland Mountains, southeasterly downslope
flow will likely keep the rain lighter. Once the front passes, a
dry slot wrapping into the system should allow partly to mostly
sunny skies to develop during the afternoon. The combination of
sunshine and warm southerly breezes will easily send temperatures
soaring into 60s. That breeze could become rather gusty,
especially if skies clear faster, and may need to be further
examined by later shifts. By late Friday, the NAMNEST shows a
line of convection forming to our west with the approaching cold
front, but this activity will likely start to dissipate due to
waning instability as it pushes into eastern Kentucky. Most of
the models show the the front faltering to our east Friday night
with only slightly colder air filtering in for Saturday. Thus,
high temperatures could again warm well into the 50s on Saturday
under partly to mostly sunny skies. Rain showers are expected to
redevelop Saturday night and persist into Sunday as the second
upper level low passes near the Ohio River. Temperatures cooling
below 0C at 850mb will allow for a changeover to snow across the
highest elevations (above 3,000 feet) on Sunday before light
precipitation tapers off. High pressure will follow Monday and
Tuesday with partly to mostly sunny skies before clouds increase
ahead of the next system on Wednesday. Sunday`s highs will be much
cooler, ranging in the low to mid 40s. A slow warming trend
ensues thereafter with highs reaching the low to mid 50s by
Wednesday. Low temperatures will also be seasonably cool, ranging
from the mid 20s to mid 30s from Sunday night through Tuesday
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 725 PM EST WED DEC 30 2020
A cold front approaching the area and is expected to track
through our forecast terminals between 06Z and 09Z. A large band
of rain just ahead, along, and behind the frontal zone will slide
eastward overnight, gradually dropping VSBYS and CIGS down into
IFR territory by late tonight. South-southwesterly winds at
around 10 kt with gusts to 20 kt or a bit higher have begun to
show sign of decreasing in intensity. Expect this trend to
continue over the next few hours, setting up a situation favorable
for some non-convective LLWS as winds aloft (LLJ) remain higher,
between 35 and 45 kts at H925 and as high as 60 kts at H850, all
from the southwest. VSBYS improve late in the forecast window but
CIGS remain low, in IFR range.
Area Forecast Discussion
National Weather Service New Orleans LA
921 PM CST Wed Dec 30 2020
Forecast generally appears on track. While no significant changes
were made to the 12-hr POPs, did make some tweaks to the timing
of showers and storms for New Year`s Eve afternoon and night in
the 3-hour POP blocks. Still looks like there will be potential
for two rounds of storms with some convection well ahead of the
main front and then a second round along the front. Main threats
continue to be damaging wind gusts and tornadoes with hail being
- Ensure you have multiple ways to receive severe weather
warnings - at least one of which will wake you up since the
severe weather threat will continue into the overnight hours
- Know where your safe shelter will be if a warning is issued for
- The safest shelter location is a small, interior room on the
lowest level of a well-built structure. Residents of
manufactured homes should try to make arrangements for alternate
shelter and plan to seek shelter in a sturdier building in the
event a tornado watch or warning is issued.
Valid through 00z Jan 1...
VIS satellite and area observations continue to indicate a broken
area of low/mid-level clouds across a large portion of SE LA -
generally along and west of I-55 which has brought CIG`s to around
06 to 08kft. Not anticipating any reductions in flight categories
with VFR forecast for all area terminals through tonight.
Otherwise, some patchy SCT/FEW low clouds will develop later today
with persistent SSE to SE winds at the surface.
A few isolated showers or storms will be possible along coastal
Mississippi daybreak Thursday. However, coverage and intensity
remains to be in question. If any activity does develop, temporary
reductions in VIS, some lightning and gusty winds may be possible
which would reduce flight categories at times. KLG
.PREV DISCUSSION... /issued 406 PM CST Wed Dec 30 2020/
SHORT TERM (This evening through Friday morning)...
Plenty to talk about here in the next few days, so let`s dive
right into it. Starting with late this afternoon evening with a
quick current overview. As discussed with the morning update
earlier, we remain largely in a prominent return flow/WAA pattern
with deep- moist ascent in progress per comparing 00Z/12Z KLIX
RAOBs (ascending base of subsidence inversion). Deeper moisture
remains generally along I-55 on to the west where more low to mid-
level clouds continue to be stuck in place. Mostly sunny skies
continue just to the east with a few low-level Cu where mostly
clear conditions should continue into the overnight hours.
Additionally, have decided to go with a low-end Wind Advisory for
SE LA parishes matching with LCH WFO as observations continue to
indicate the strongest gusty wind potential caused by tightening
and dropping MSL pressure gradient in the region. This should
relax some by late evening/early tonight along with eventual
decoupling of the PBL around and after the sun sets. Zooming out a
bit taking a CONUS look at the synoptic pattern illustrates a
very impressive and deep upper-low digging across northern Mexico,
well south of the four corners region (around the order of 10 to
20dm lower than CFSR Climatology indicating an anomalously strong,
deep low). Downstream of this, strong low-level winds continue
across most of western and central Louisiana which has helped
develop west of our area; pushing as far east as around BTR. This
activity was collocated with an enhancement of the low-level jet
which is quickly ejecting northward, and will drag any associated
lift and shower activity into southern AR/central MS this evening.
For us here locally, it will be mostly dry with blended guidance
in good agreement keeping breezy southeasterly winds and a few
The first focus of any potential shower/storm chances comes early
Thursday morning along or southeast of coastal Plaquemines parish;
which CAM`s have been hinting at for a while now but has been
pulling back a bit more on area coverage (especially latest HRRR
trends) since better overall synoptic scale ascent remains well to
the west. PoP`s have been trending higher in this location over
the past few days, but given how CAM`s have been handling
mesoscale feature better, have decided to trend PoPs downwards
into the 20`s to 40`s along coastal MS where this potential
cluster will eventually end up come around daybreak. Overall not
too concerned with this cluster as deep-layer shear magnitudes are
very limited, but will be closely monitored regardless as
directional shear is there, and will warrant watching IF anything
can develop in this region.
Going into the morning hours on Thursday, the strong upper-low
out west will press more towards the east into southern Texas, and
eventually take on a negative tilt with rapid cyclogenesis across
the SE TX Gulf coastline. We will see a lull in activity during
this time frame (12Z to 18Z) but cant rule out an isolated shallow
shower or two - especially near marine areas. Winds will be
picking up out ahead of this deepening low as well, and will
investigate the need for a Wind Advisory across our area in
subsequent shifts tonight or early tomorrow. By around noon
Thursday, we will begin to focus on what will likely be a quick
ignition of showers and storms along a northward surging, weak
warm front along and south of I-10/12 as deep-layer ascent
increases, combined with some subtle fueling from diurnal
destabilization with CAPE ranging in the range of 800-1200J/kg,
MLCAPE in the 700-900J/kg range. An in-depth investigation with
environmental soundings ahead of this disturbance from CAM
guidance still shows a lag of higher magnitude deep-layer shear
(0-1km SRH in the 100-150m2/s2 range/ 0-3km SRH in the 200 m2/s2
range). Given environmental hodographs and low/limited
instability, not going to be too concerned with this initial wave
just yet OR - any threat in the THU 18Z to FRI 00Z time frame may
be limited. However, shear will be increasing hour by hour,
especially in the 21Z to 03Z time frame and with any lingering
pre-frontal convection, may evolve into an increasing threat.
Regardless, any storm activity from this disturbance anchored
across our CWA racing to the north will be closely monitored in
this time frame. H5 temperatures in the -10.5 to -11.5 range will
introduce a small hail threat, and any individual storm may
contain damaging wind gusts. It is worth mentioning that
sometimes, especially in our area, strong directional shear can
sometimes overshadow the lack of shear magnitude, especially since
we typically see shallow showers with low LCL`s along the
coastline that may lead to quick, weak spin up tornadoes or
waterspouts. This initial wave, by far, is not a substantial
threat - but may evolve to become one especially by late afternoon
As we continue into the evening hours, the next focus becomes the
front itself racing quickly east and entering our far western CWA
around 7 to 10PM. This is where maximized shear/forcing will
reside with very impressive 0-1km SRH ranging 300-350+m2/s2, over
400+m2/s2 0-3km SRH. Environmental dry air entrainment will also
push in along with the line helping to drag in much more
impressive lapse rates in and around 6 to 6.5C/km (impressive
enough for the northern Gulf coast). Storm motions will be very
fast along what will likely be a very thin line of thunderstorms
(anywhere on the order of 55 to 60kt individual storm motions
bearing from 180/190). Overall threat timing along with the
highest threat region will be for areas along and north of I-10/12
collocated with better shear, with timing from about 7 to 10PM
for far western areas, to around 5 to 7AM across coastal MS as the
line races east. Storm mode will include a thin QLCS with fast
south to north moving embedded mesovortexes that may produce
quick spin up tornadoes. Cant rule out a strong tornado or two
especially in the Enhanced Risk area outlooked by SPC (10% TOR
probs). However, overall forecast STP/EHI is not pinging on
anything alarming given limited instability. A classing low
CAPE/high shear environment that can sometimes over produce or
under produce which leads to a low confidence forecast.
Several things to consider here includes how much overall
coverage will we see with the lead disturbance early Thursday
afternoon. Greater coverage will limit any supportive instability
and potentially cut off moisture supply to the area of best
forcing, making for a real "pitiful" looking line - lowering
overall severe risk. Shear is there in an event like this, but
many mesoscale caveats exits that can lead to less of as risk.
Additionally, CIPS guidance does hint at some historic events -
one more notably December 28th 2015 (very similar synoptic scale
set up) that did lead to a few small tornadoes. Good news is we
will get this line out of here quickly early Friday followed by
gusty winds out of the southwest and clearing conditions/cooler
temperatures on Friday.
LONG TERM (Friday through Wednesday)...
After this system gets out of here, the next (slightly weaker)
closed low embedded in a deep southern Plains trough rotates east
across northern mexico, which will help keep upper-level flow out
of the southwest. This trough swings across the region on
Saturday, likely igniting a surface low and associated rain/storms
well to our east giving us a re-enforcing shot of post-frontal
cooler air. We will not see the coolest air until early Sunday
morning with widespread mid to upper 30`s possible, aided by
radiative cooling/subsidence caused by high pressure settling into
the area. Highs will be generally seasonal, perhaps slightly
below normal on Sunday but will moderate going into early to
middle portions of next week. Not seeing any additional hazardous
weather potential through the next 7 days which is some great
news. Might see some light rain chances on Thursday with a weak
impulse/shortwave trough rides along a quasi-zonal mid-level flow
aloft. But overall, relatively quiet weather expected next week.
But things can change. We will keep you posted. KLG
Persistent southeasterly onshore flow is expected out ahead of a
developing strong storm system to the west. Small Craft Advisories
are in effect for a large potion of the area due to increased
wind/wind gusts and increasing seas. We may see a temporary lull
in gusty winds tonight, but will likely pick back up early
tomorrow lasting through the overnight hours as a cold front races
east across the region. A few strong or severe storms will be
possible, with strong wind gusts greater than 34kts and
waterspouts the main threats. A reinforcing front arrives on
Saturday helping to increase northwesterly winds but will likely
remain below advisory criteria for now. Quiet weather conditions
will extend into early to middle parts of next week. KLG
.PRELIMINARY POINT TEMPS/POPS...
MCB 61 74 52 65 / 10 70 80 0
BTR 62 75 52 63 / 20 80 90 0
ASD 61 75 55 67 / 30 80 80 10
MSY 63 75 57 66 / 20 80 80 0
GPT 62 72 58 68 / 40 70 90 20
PQL 60 75 58 69 / 40 60 90 30
GM...Small Craft Advisory until 6 PM CST Thursday for GMZ536-538-552-
Small Craft Advisory from 6 AM to 6 PM CST Thursday for GMZ550.
Small Craft Advisory until 6 AM CST Thursday for GMZ534.
GM...Small Craft Advisory until 6 PM CST Thursday for GMZ538-552-555-
Area Forecast Discussion
National Weather Service Omaha/Valley NE
923 PM CST Wed Dec 30 2020
Issued at 920 PM CST Wed Dec 30 2020
We are starting to see some areas of fog, locally dense, in parts
of the Platte River Valley where skies are mostly clear. RAP and
HRRR model output suggest that fog will expand some overnight
as it slowly lifts to the north and east through Thursday mid
morning. Added mention of areas of dense fog to the forecast, but
did not issue at advisory at this point. One may be needed yet
though within the next several hours, depending on how widespread
Issued at 333 PM CST Wed Dec 30 2020
Temps range from mid-20s to 30F as of 21Z. Day cloud phase
satellite imagery reveals Nebraska and Iowa covered in fresh
snow. In fact, the national snowfall analysis shows the entirety
of both states have received some snow in the past 72 hours.
This snow will help keep temps low overnight as high pressure
settles in. The clear skies, diminished winds, and deep snow pack
will allow temps to slip into single digits for all but our far
western CWA. It`ll be chilly under a bright December moon.
Eppley`s forecast low of 7F for the 2020`s last morning would be
only the the 14th time slipping into single digits this year.
Some sub-zero lows are possible in low-lying areas. Have driven
temps close to the 20th percentile of solutions.
I`ve introduced patchy fog into the forecast for much of southwest
Iowa, southeast Nebraska, and the Missouri River valley. Have
been conservative, so this area may need to be expanded by the
Thursday will be cool despite the mostly sunny skies. The low sun
angle will be no match for the snow`s high albedo. Expect mid-20s
to lower 30s. Patchy fog may develop on Thursday night, too.
The main forecast concern will be the possible impacts of a
powerful low sweeping in from Mexico of all places. As the low
closes tonight, it will take a sharp turn north, following the
jet`s path around a Caribbean high. The system brings an anomalous
amount of moisture to Missouri and Kansas Thursday night and
Friday. We would expect these values of precipitable water to
occur in only about 10% of Decembers.
As models converge on a solution, the expected gradient continues
to tighten. Only 4 of EC ensembles suggested more than an inch of
snow was possible in Omaha, but the 12Z run has all members dry.
One in five indicate at least that much snow for Nebraska City,
and a majority in Falls City. As it stands, we`re expecting a
dusting or less for all but the the extreme southeastern counties
in the CWA with 0-3" in FNB the highest possible total. Expect a
tight northern cut-off on the snow as this abnormally moist
airmass butts against some dry air from the north. This glancing
blow should have the snow falling only between 3 am and 3 pm on
Friday. A wintry mix is expected for parts of Iowa and Missouri,
but remain outside the confines of this CWA. We`ll just see
Return flow develops on Saturday, setting the stage for warmer
temps for the weekend`s second half with melting snow expected
after lunch each day next week.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 525 PM CST Wed Dec 30 2020
The area of stratocumulus extending from north to east of KOMA
may be in the area for a few hours this evening, but then it seems
like it should move off to the east. Fog should develop at mainly
KOMA and KLNK, with KOMA with visibilities possibly under 3
miles. Any fog that develops should lift by mid morning, with VFR
conditions and a southerly breeze the rest of the day.
Area Forecast Discussion
National Weather Service Pocatello ID
755 PM MST Wed Dec 30 2020
.UPDATE...Have updated the forecast through the overnight hours to
nudge the forecast more in the direction of both observational
trends as well as 00Z high-resolution model guidance trends. The
update was necessitated because snow showers had already entered
the Sawtooths and Wood River Valley, and radar echos were
capturing developing snow showers across the Magic Valley and
south hills as well. The 00Z models, the HRRR specifically, have
captured this trend nicely and have updated the forecast to
reflect these trends. The recently developed snow showers should
continue on an eastward trajectory towards the Snake Plain over
the next hour or two before the main area of snow showers arrives
across the eastern Magic Valley, southern Snake Plain and south
hills after midnight. The latest high-resolution guidance indicate
a re-intensification of a broad shield of snow showers as the
mid-level trough approaches from the mid-morning through early
afternoon hours. These snow showers are depicted generally along
and east of a Twin Falls to Island Park line. Have nudged the
forecast in this direction as well. The previous discussion
.PREV DISCUSSION... /issued 133 PM MST Wed Dec 30 2020/
SHORT TERM...Tonight through Fri night. An incoming trough is
packing some moisture and will leave some light to moderate snow
accumulations in eastern Idaho starting this evening in the
central Idaho mountains and before midnight spreading to the ID-WY
border. The trend from the previous forecast this morning is only
slightly higher, with 95 percent of the mountain/highland area
receiving less than 6 inches of snow, and Snake River
plain/eastern Magic Valley receiving 0.5 inch in the warmer Magic
Valley to 3 inches in the north end of the Snake River plain. The
associated front is expected to sweep through during the morning
hours on Thu, but wind on either side of the front should stay
light. There is some southerly wind tonight that will bring in a
warm frontal inversion that could allow at least partial melting
and then a partial re-freeze for a few hours this evening, making
for icy conditions on roads and highways. The area most affected
by this will be the Wood River valley and Stanley basin, and the
eastern Magic Valley. This should be over by midnight for all
locations. Much lighter snow falls during the day Thu, with only
the area north and east of Ashton in the northeast corner of the
forecast area receiving more than an inch; most of the rest of the
eastern highlands could receiving 0.5 to 1 inch, and the central
Idaho mountains, south central highlands, and the valley and plain
locations getting less than 0.5 inch during the day Thu. Thu night
will be dry, with the clearer skies and northerly airflow dropping
temperatures 10 to 15 deg F from tonight`s lows, with single
digits returning to the Snake River plain. A drier Fri should see
temperatures about the same as Thu, then Fri night the next storm
starts spreading cloudiness during the evening and a chance of
precipitation for the northern half of the forecast area, but the
brunt of this storm arrives in the extended forecast. This will
put Fri night lows in the teens for the populated areas.
Have re-issued the Special Weather Statement with an emphasis on
the potential for icy road conditions in the west, and the heavier
snowfall in the northeast. Did not add any forecast zones to the
LONG TERM...Saturday through Wednesday. A constant flow of moisture
will lead to better chances of mountain snow and a mix in the lower
elevations almost daily heading into next week. For Saturday, light
precipitation is expected mainly for the Sawtooths and eastern
highlands...although there is much smaller chance elsewhere. Sunday
through early Tuesday looks very wet as we get a stronger surge of
moisture potentially working east of the Cascades into our area.
While the mountains look to see a fairly steady stream of moisture,
the Snake Plain/Magic Valley should see breaks between each
individual storm moving across the state during that timeframe. This
will be a warmer and windy pattern. This will lead to a mix of rain
and snow across portions of the Magic Valley and Lower Snake Plain.
The wind MAY create some blowing and drifting issues at higher
elevations. The caveat here limiting that would be a "wetter" snow
vs powder. Snow amounts have been trending down a bit, but favored
areas of the Sawtooths could see 5-10" with a little more than that
in valley locations. For the eastern highlands, we could 3-7" for
the Big Holes and Island Park area. For the Shoshone Lava Beds area,
1-4" is not out of the question. Elsewhere, downslope and warm
temperatures will limit snowfall potential. These numbers are NOT
SET IN STONE, as we will need to see just how much moisture ends up
getting past the Cascades...and with these types of storms we
usually don`t get a better picture until we get a little closer to
the event. Another bigger push of moisture arrives sometime later
AVIATION...Conditions have improved at all TAF sites through the
morning, as we turn attention toward potential impacts from snow and
lower ceilings through tomorrow. We are currently VFR, awaiting to
see if the first band of precipitation actually falls enough to
impact airports. It seems a little bit too dry for snow to fall, BUT
we are still thinking some impacts are possible with this first
round. Confidence is LOW for the first few hours, and IF it does
start snowing, look for MVFR/high end IFR conditions. Trends are
showing that impacts are more likely with the band of snow moving in
later this evening through tomorrow morning. We are forecasting
MVFR/IFR due to snow and low clouds with this band. The ban should
clear SUN closer to sunrise with improving weather. The band should
stay going through at least the morning hours at BYI, PIH, IDA and
DIJ...with IFR conditions. We could see a brief dip to LIFR if
snowfall temporarily increases intensity-wise. Conditions should
slowly improve tomorrow afternoon. Keyes
Area Forecast Discussion
National Weather Service Blacksburg VA
923 PM EST Wed Dec 30 2020
A cold front slowly approaches from the west tonight, stalling
across NC Thursday afternoon. A strong low pressure area will
move across the mid Mississippi Valley by Friday and into the
Great Lakes Friday night. This system will bring another soaking
rain to the area.
.NEAR TERM /THROUGH THURSDAY/...
As of 920 PM EST Wednesday...
Patchy fog overnight with only very light showers in far
southeast Piedmont and also far western slopes toward morning.
Zone of light showers has shifted east of the forecast area
this evening and not seeing any reports of drizzle although
there could still be some in pockets near the Blue Ridge of NW
NC and SW VA. Patchy fog also pretty limited at 9pm and is
forming more along Blue Ridge but expect will eventually show
up in other locations along either side of the Blue Ridge
overnight. Only made some minor adjustments for PoPs and
temperatures based on latest observations but otherwise no
notable changes for rest of tonight.
Cold front still expected to approach western slopes by
morning and weaken, with light showers reaching far western
slopes between 5 and 6am. Still a sprinkle or two in far
southeast Piedmont later tonight per latest runs of HRRR from
what can be seen on regional radars moving north into south-
Prev discussion as of 530 PM EST Wednesday...
Patchy drizzle a fog started to work it`s way up the Blue Ridge
in NC and otherwise lowering ceilings in a lot of locations due
to increasing overrunning with low-level SW jet riding over the
sfc high pressure. This is likely to keep spreading north a bit
more after dark, especially along and east of the Blue Ridge,
but there some indications that some mountain locations west of
the Blue Ridge may even get some breaks in clouds at some point,
with the exception of far west as weak frontal boundary
approaches. In addition to adding some more areas of drizzle and
fog this evening, reduced the lower elevation winds since there
is little mixing going on at this point. Only the ridges still
have gusts into the 20-30mph range and that should continue
most of the night. No other changes at this point.
Previous discussion as of 140 PM EST Wednesday...
Shower threat increasing but no hazards anticipated this period
Clouds increasing across southern Virginia from NC, with warm
advection in the mid levels and in advance of a front that was
located from Michigan to western TN this afternoon. The front tracks
into our region Thursday. Models continue to paint 2 areas of higher
pops, one over the coastal plains of NC with better low level flux
of moisture and along the front from mid TN to the central
Appalachians. There remains a lull between these two areas, so have
trimmed pops back tonight into Thursday from especially along and
either side of the Blue Ridge.
Not expecting much in the way of rainfall tonight-Thursday, with
better threat arriving late Thu night as the warm front starts to
track back north in advance of the upper low over eastern
Oklahoma/western Arkansas. At play is a wedge of high pressure
centered over New York and temp profiles are mainly keeping things
of the liquid variety. Some of the colder guidance such as the NAM
have a couple hours around 5-8am Friday of potential ice/sleet in
along the Alleghanys. But at the moment confidence is not high on
this being impactful.
Higher rainfall amounts will be situated from the NC
mountains/foothills into the Virginia piedmont late Thu night, but
overall amounts are looking a half inch or less.
With plenty of clouds, temperatures tonight will be milder in the
mid 30s to lower 40s. Southwest flow along the front Thursday and
some potential sunshine will lead to warmer highs in the upper 40s
to mid 50s west, to upper 50s to lower 60s east.
Temperatures will drop close to freezing in the higher mountains of
Bath/Rockbridge/Amherst Thu night, where a potential for light ice
exists, with most in the upper 30s to lower 40s.
Forecast confidence is above average on winds, and average on
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 154 PM EST Wednesday...
Some freezing rain or sleet possible early Friday along the northern
High pressure will wedge south from New England into North Carolina
Friday. A closed low tracking northeast across the Red River Valley
of Oklahoma will push a series of disturbances with warm moist
air over the wedge. The trend of the model solutions has been to
push colder air into northern portions of the forecast area.
Added the mention of a period of freezing rain and sleet for the
higher elevations Friday morning. Then, most locations will
transition to light to moderate rain Friday afternoon into
Friday evening. The day 3 SPC Convective Outlook highlighted
any severe storms will be south of our area. High temperatures
Friday will range from around 40 degrees in the north to the mid
50s in the far west. Believe the models are too fast in
removing wedge and elected to slow the exit of the precipitation
Friday night. With a slower approach, low clouds, drizzle and
fog will be in the area into Saturday morning. Low temperatures
Friday night will vary from the mid 30s in the northern
mountains to the upper 40s in the piedmont. Rainfall amounts
Friday will vary from around three tenths of an inch to around
an inch and a half. The model trends continue to be lower on QPF
totals for this event.
As the front moves off the East coast, a low pressure wave forms
along it Saturday and sends showers back to the area Saturday
afternoon into Saturday night. High temperatures will be mild on
Saturday generally from the upper 40s in the northwest mountains to
the upper 60s in the piedmont. Low temperatures Saturday night into
Sunday morning will be in the mid 30s in the west to the mid 40s in
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 154 PM EST Wednesday...
Weather fairly quiet for our region after Sunday showers.
Low pressure will lift northeastward into the New England coast
Sunday into Monday. Most of the precipitation will fall as rain
Sunday. On the backside of the low center, colder air looks to
arrive slowly limiting any snow to the higher ridges of Southeast
West Virginia Sunday. High pressure and ridging will build north
into the central Appalachians Monday into Tuesday. The ridge aloft
will flatten on Wednesday, this will allow an upper trough and
associated cold front to approach the Ohio Valley.
Temperatures will be near normal during the long term period.
Low to moderate confidence in the long term forecast.
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
As of 705 PM EST Wednesday...
Ceilings will likely remain VFR at western TAF sites, BLF and
LWB, most of the night, but otherwise MVFR and even dropping to
IFR at LYH and DAN overnight with weak wedge and overrunning.
Some brief light rain or drizzle is also possible mainly at DAN
As a weak front approaches the western slopes of the
Appalachians Thursday morning expect conditions to deteriorate
to MVFR or perhaps briefly IFR with a few showers around, and
then continue to drop to IFR ceilings during the day with a
shower or two still possible as the front slowly pushes through
but weakens. Not expecting an all day rain. In the east, MVFR
conditions likely will prevail most of the day, but by close to
evening they could begin to drop and again toward or below IFR
with the chances for more widespread showers increasing.
Winds will be light and variable at the TAF sites overnight,
but gusty from the south along higher ridges, thus concern for
low-level wind shear at all TAF sites given much stronger winds
at ridge top level. These ridge top winds weaken somewhat by
morning thus no need to carry low-level wind shear during the
day, and surface winds will generally remain light and variable
with weakening front or surface trough overhead.
Forecast confidence is moderate on at least having sub-VFR cigs
by tonight at most/if not all taf sites, but low on how low
cigs/vsbys will reach and threat of rain.
Extended Aviation Discussion...
MVFR/IFR conditions are expected through the end of the week as
a wedge of high pressure moves in from the north and brings
surface winds out of the northeast, especially in the Piedmont,
by Thursday night into Friday. A strong frontal system will
bring widespread rainfall to the region spreading over the wedge
Thursday night and especially Friday. There is an increasing
potential for freezing rain and light ice accumulations mainly
along ridges as well for Friday, but potential appears low for
any freezing rain at the TAF sites so far. Conditions remain
unsettled with sub- VFR conditions and at least more light
precipitation later in the weekend.
High pressure should bring a return to VFR by Monday.