Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/05/21

Area Forecast Discussion

National Weather Service Blacksburg VA

 931 PM EST Thu Feb 4 2021

.SYNOPSIS...
A wintry mix of precipitation is expected tonight as a cold
front crosses the Mid-Atlantic region. Expect a 4 to 8 hour
period of mainly light precipitation...initially starting
as snow or sleet, then transitioning to freezing rain or rain
depending on the surface temperature.    The front is
expected to clear the area Friday morning with a period of
drying expected Friday Afternoon.

A winter storm is possible this weekend.  The front that
passes across the region tonight and Friday is expected to
stall along the Gulf Coast.  A wave of low pressure is then
forecast to develop along the front, and move northeast to
along the Mid-Atlantic Coast by Sunday morning.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 930 PM EST Thursday...

Initial batch of light precipitation was a mixed bag as it moved
over our very dry airmass and caused a good deal of evaporative
cooling, but did not saturate the boundary layer. This has us
trending a bit below guidance mainly form the NC mountains up
into the Grayson Highlands. Next batch of steadier/heavier
precipitation is now moving in from the west, with the
expectation for additional evaporative cooling. Believe the
combination of surface temps and boundary layer temp profiles in
BufKit support a continued wintry mix with the greatest
potential for some snow/sleet/ice accumulation from northern
portions of the NRV up into Greenbrier WV and the Alleghany
Highlands, as well as down from the Grayson Highlands in VA
through the mountains of NC. Winter Weather Advisory already in
place up north, but now have greater confidence in icing
potential to place the NC mountains/Grayson Highlands into an
advisory as well. The remainder of the region in between will
also see a wintry mix, but current and expected temperatures
seem to be indicating potential for less widespread hazardous
conditions so have issued a Special Weather Statement to bring
attention to the situation and will monitor closely to see if
conditions change.

Previous discussion...

A storm system over the Upper Midwest will cross the Ohio
Valley and Great Lakes Region tonight...the associated cold
front crossing the Mid-Atlantic Region early Friday. Expect
onset of precipitation across all areas west of the Blue Ridge
before midnight, then spreading to areas east of the Blue Ridge
after midnight. Forecast challenge is the p-type. Model
consensus is for a +2 to +3 deg C warm nose to advect north and
in advance of the cold front, this warm nose generally resulting
in p-types of something other than snow. Our current sounding
is very dry in the low levels, so any precipitation at the onset
may fall in the form of snow or sleet due to wetbulb affects.
Once the low levels become saturated, then expect a transition
to either freezing rain or rain, which will be dictated by the
actual surface temperature at the time.

The ground is frozen in many of the mountain locations. Up north
near I-64 from the Greenbrier Valley into the VA Highlands, the
depth of cold air will support a bit more frozen precip in
addition to a longer duration period of freezing rain snow/sleet
total may fall into the 1-3 inch range in addition to a glaze
of ice from the freezing rain. The over all consensus in
guidance is for lower QPF the farther south you go in addition
to slightly warmer temperatures. I say warm, but the net effect
from the wet bulbing will be to draw the temperature down pretty
close to freezing for all areas west of the Blue Ridge... so it
will turn out to be a very cold rain at the very least. Model
consensus is for about a tenth to as much as a third of an inch
of liquid equivalent QPF... so this is event is more of a
nuisance than anything else.

The front is expected to move east and exit the forecast area by
9AM Friday morning, bringing an end to precipitation from west
to east between 4AM-8AM. Post frontal drying is expected to
bring clearing to the forecast area by mid-day, with mostly
sunny conditions anticipated Friday afternoon...temperatures
rebounding into the upper 30s to lower 40s west of the Blue
Ridge and into the upper 40s to lower 50s east of the Blue
Ridge.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM EST Thursday...

Increasing chances for snow late this weekend, temperatures stay
chilly.

A broad surface low concurrent with an upper trough over southern
Canada will intensify Friday night and swing a cold front off the
Atlantic coast. An upper shortwave in the southern CONUS will come
around the trough late on Saturday, and encourage cyclogenesis just
off the Carolina coast overnight into Sunday morning. Latest model
runs have brought most global models into better agreement with a
more northward/westward track. This means that the possibility of
snow has been reintroduced into our forecast area, especially
towards the Piedmont. Ensemble guidance indicates high probability
of this being a lower impact system. QPF is around 0.10-0.25" for
Saturday night and Sunday morning, and with temperature profiles
indicating the event begins as rain and turns over to snow later
Saturday night, not all of that will be converted to snow.

Given the recent volatile nature deterministic models have displayed
around Saturday night`s weather, generally staying conservative on
this forecast and putting more weight into ensemble/probabilistic
guidance. If the next few runs continue to narrow towards this
northerly solution, then will give them more consideration in future
forecasts. If they continue to flip flop, then will continue to
stick with ensemble guidance.

A transient surface high will push out any precipitation Sunday
morning, and expect dry weather for Sunday afternoon. Diurnal
temperature swings will be quite large during this portion of the
forecast. Highs will be in the upper 30s west of the Blue Ridge,
upper 40s and at times 50s east. Meanwhile lows will get down into
the teens and 20s every night.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 500 AM EST Wednesday...

A large persistent trough over southern Canada will bring a couple
waves through the CONUS during the portion of the forecast. Timing
and impacts are not precise, but currently seems that Tuesday night
and Wednesday night will see some precipitation with frontal
passage. Both the GFS and the ECMWF have surface lows for that
system riding up the New England coast and intensifying in the
northeast.

Temperatures are on a downward trend for late next week. By
Wednesday and Thursday night, temps will be 10-15 below normal.
However, this should be taken with a grain of salt, as this current
upcoming weekend initially looked to feel the icy grip of
significant arctic air, but has since mellowed out.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
As of 735 PM EST Thursday...

East of the Blue Ridge, expect VFR flight conditions, with
a period of MVFR cigs possible as showers/maybe some sleet move
through around daybreak. West of the Blue Ridge, VFR early in
the TAF period will trend to IFR as rain/wintry mix of precipitation
arrives, then gradually trend back to VFR late Friday morning/early
afternoon with a rapid exit of precipitation. Expect some icing
of aircraft and runways tonight at KLWB...and possibly to a much
lesser extent at KBCB.

Low level winds will amplify considerably tonight but do not
expect good mixing so will only indicate gusts up on the hill at
the KBLF airfield. Much better mixing tomorrow so expect gusty
conditions all TAF sites by the afternoon.

Average confidence for wind and ceilings. Low confidence in
precipitation, precipitation type, and visibilities.

Extended Aviation Discussion...

A wave of low pressure is expected to develop along a stalled front
Saturday night and move northeast to the Mid- Atlantic Coast by
early Sunday. This is a significant change to previous models
runs and now suggests parts of the Mid-Atlantic region will be
subject to winter storm conditions Saturday night and Sunday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Winter Weather Advisory until noon EST Friday for VAZ015-
     018>020.
NC...Winter Weather Advisory until noon EST Friday for NCZ001-002-
     018.
WV...Winter Weather Advisory until noon EST Friday for WVZ043-044-
     507.
     Winter Weather Advisory until 1 PM EST Friday for WVZ508.

&&

$$
SYNOPSIS...PM
NEAR TERM...MBS/PM
SHORT TERM...VFJ
LONG TERM...VFJ
AVIATION...MBS/PM