Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/29/20

Area Forecast Discussion

National Weather Service Blacksburg VA

 828 PM EST Sat Nov 28 2020

.SYNOPSIS...
High pressure will drift east of the area by Sunday. A
significant low pressure system will approach the area from the
southwest later Sunday and bring significant rainfall and
breezy south winds Sunday night through early Monday, with much
colder air, strong northwest winds, and accumulating snow
showers on the western slopes by late Monday through Tuesday. A
few thunderstorms cannot be ruled out early Monday mainly
southeast of Danville.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 825 PM EST Saturday...

Satellite imagery continues to show clear skies over the region
with just some wispy high clouds pushing into northwest NC.
Expect conditions will remain quite favorable for radiational
cooling and make for some chilly readings by daybreak,
especially in the valleys west of the Blue Ridge. Expect any
fog will remain confined to the river valleys right near
waterways west of the Ridge.

Previous discussion...

Broad high pressure over the Ohio River valley and into central
Appalachians will keep winds very light overnight and should keep
any clouds suppressed to the south, resulting in nearly ideal
radiational cooling conditions. This should lead to much colder
valleys compared to milder ridges, although winds even on ridges
will be rather light so perhaps not as extreme differences as
would be the case with a ridgetop breeze going. Stayed close to
guidance for lows except did nudge up a bit on the ridges.

Sunday still a little on the mild side of normal with mostly
sunny skies for the first half of the day and light winds, but
then increasing high clouds by afternoon in advance of
approaching significant low pressure system from the southwest.
Consensus of guidance a little slower with any arrival of light
rain across the south until after 00Z Sunday evening, so really
no mentionable PoP for the daytime period Sunday.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 100 PM EST Saturday...

A short wave over southwest Canada and a closed low over New Mexico
will move east, merging into a deep closed upper low over the Ohio
Valley. Then by Tuesday night the upper low will be entering
Ontario. Synoptic models were in very good agreement through Tuesday
on the location and intensity of the low. Most questionable
ingredient for any severe weather threat is the amount of
instability. 12Z models continued to show the potential for a small
amount of instability east of a Buckingham to Danville line for late
Sunday night and Monday morning. Will keep the probability of
thunderstorms at slight chance due to the unfavorable time of day.

The associated surface low moves from Mississippi to Pennsylvania
Sunday and night and Monday. The warm front will lift north as the
surface based wedge erodes on Monday, followed by the west to east
moving cold front Monday afternoon and evening.

Best upslope and isentropic lift will be Sunday night, aided by a 25
to 35 knot southeast low level jet. The precipitation will help
develop an in-situ wedge over southwest Virginia and northern North
Carolina. Planning on mild temperatures, 10 to 20 degrees above
normal, ahead of this system Sunday night then falling temperatures
Monday afternoon in the mountains. Highs on Tuesday afternoon will
be 10 to 20 degrees below normal, likely not getting out of the 20s
at higher elevations.

The strongest cold air advection is Monday afternoon and evening,
bringing 850 mb temperatures down to the -4 to -8 range by Tuesday
morning. The low level jet in this time frame is 25 to 35 kts but
then becomes stronger Tuesday night. Pressure rises Monday evening
will be around +7mb/6hr, more than enough when combined with cold
air advection and pressure gradient to enhance wind speeds and
gusts.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 100 PM EST Saturday...

500 MB heights rise with somewhat flat upper ridging over the Mid
Atlantic and southeast United States on Wednesday and Thursday as a
large upper low deepens over the central United States. This low
reaches the eastern United States on Saturday.

Surface high pressure will cover the central and southern
Appalachians on Wednesday night and Thursday. Gusty winds will
continue through Wednesday morning, but by Wednesday evening winds
will become light and will decouple in the valleys. Will have
minimum temperatures Wednesday night below guidance in the mountain
valleys and in locations that are expected to have snow on the
ground.

A surface low pressure system will track from the Lower Mississippi
Valley into the Tennessee Valley Friday and Saturday. Large
differences in location on the low on the models. WPC favors leaning
toward a low along the Gulf Coast on Friday tracking to the Carolina
coast by Saturday. This will bring a higher probability of
precipitation to North Carolina and southern Virginia as early as
Friday morning. Will trend temperatures to the cooler side of
guidance with the low passing to the south as well as clouds and
rain expected.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
As of 620 PM EST Saturday...

VFR conditions expected all sites through the valid period. Good
radiational cooling may generate some fog overnight, but expect
it will be confined to the river valleys west of the Blue Ridge.
May see some affect at KLWB and KBCB toward daybreak but confidence
is not high so will omit from TAFs and amend if needed.

Winds will generally be light with little impact to aircraft
operations. However, low level flow will amplify toward the end
of the valid period in the mountains with some gusty conditions
developing on the hilltops and will indicate this at KBLF.

Extended Aviation Discussion...

Conditions will deteriorate rapidly Sunday evening as a strong
negatively tilted upper low rotates northeast from the
southeastern U.S. Potentially multiple significant weather
impacts are expected to arrive with this system Sunday evening
continuing into Monday and perhaps even Tuesday. Poor to very
poor aviation conditions expected Sunday night through Tuesday.
For Sunday night and Monday, fairly widespread IFR conditions
developing from south to north Sunday evening through early
Monday, with periods of heavy rain, gusty southeast winds
especially at KBLF, and possibly a thunderstorm or two southeast
of KDAN, with winds then shifting southwest to west during the
day Monday. Then, as colder air wraps into the region from the
northwest Monday night on the back side of this strong system,
upslope rain showers will transition to snow showers in the
western mountains, with some gradual improvements east of the
Blue Ridge. Strong and gusty winds will increase from the
northwest by late Monday lasting into Tuesday. MVFR to IFR
conditions are likely to persist at KBLF and KLWB through much
of Tuesday with upslope snow showers.


VFR conditions should return for a couple of days to the entire
area by Wednesday with the next weather system and sub-VFR
conditions arriving as early as late Friday or early Saturday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...RAB/SK
NEAR TERM...MBS/SK
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...MBS/SK