Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/28/20

Area Forecast Discussion

National Weather Service Blacksburg VA

 623 PM EST Fri Nov 27 2020

.SYNOPSIS...
High pressure will cover the Ohio Valley and Mid Atlantic region
through Saturday night along with dry weather. Sunday night through
Tuesday night a deep low pressure system will track from the Gulf
Coast into southeast Canada. This will bring rain and wind to the
area Sunday night and Monday followed by very windy and much colder
weather on Monday night through Tuesday night, along with mountain
snow showers.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 620 PM EST Friday...

A healthy deck of mid/high clouds continues to push over the region
from the southwest. Expect the clouds will be thick enough to
slow radiational cooling and lessen fog potential overnight. Also
expect some low clouds to push in from the west late associated
with a very weak frontal boundary, leaving the hilltops obscured
in upslope clouds and possibly some patchy drizzle/sprinkles.

Previous discussion...

Two pieces of short wave energy within a long wave trough in
the northern stream cross southeast Canada and the northeast
United States tonight and Saturday.

For the Mid Atlantic region and central Appalachians,500MB
heights fall slightly a the trough axis will be offshore by the
end of the day Saturday.

Models were showing a strip of 30 to 40 knot northwest low level
winds along the southern Blue Ridge late tonight into Saturday
morning. Will be increasing wind speeds and gusts along the ridge
line south of Roanoke into northwest North Carolina.

The clouds over the Middle and Lower Mississippi valley will expand
into the area late this evening. Most of these clouds will
clear the foothills and piedmont on Saturday so plenty of
sunshine and another day with above normal temperatures.
Stratocumulus will remain over the mountains through the
morning, but even western slopes will clear out for the
afternoon. Enough cloud cover early in the day to keep maximum
temperatures close to normal.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 115 PM EST Friday...

Surface high pressure will jog across the region Saturday night into
Sunday. The center of this ridge will move off the NC/VA coast
Sunday night, leaving the western edge over the area. Overrunning
moisture and rain from a southern stream complex across the southern
states will then create and enhance an insitu wedge over the area
Sunday night into part of the day Monday.

The southern stream complex will consist of an upper level low
moving over the Red River Valley Saturday night, the Tennessee
Valley Sunday and then into the Ohio Valley Sunday night into
Monday. The surface low forms along the Texas coast then joins the
upper level low when it is in the Tennessee Valley. This system
becomes occluded over the Ohio Valley Sunday night into Monday. A
northern stream upper level low over the Great Lakes will phase with
the southern stream system on Monday to create a new colder closed
lower over the Ohio Valley. This system will slowly move to the
northeast Monday night into Tuesday.

This Sunday night into Tuesday system is not only complex but brings
a multi-faceted range of weather features along with it.

1) Strong Dynamics and a negative-tilted trough will interact with
an eroding wedge to possibly bring rotating storms and heavy rain to
the area Sunday night into Monday morning. Models current have a
triple point tracking in the vicinity of Southside VA which supports
a strong convection case. Rainfall amounts could average 1-2 inches
along and east of the Blue Ridge, under an inch along western
slopes. On the other side of the coin, models have a habit of
eroding the wedge to quick in our neck of the woods. If a line of
convection across the southeastern states is strong enough, it may
rob moisture coming into the area. If this does happen, heavy rain
chances will be lower and the wedge may hang around a little longer.

2) A dry slot is expected over the area Monday afternoon. By this
time the wedge should be gone with temperatures jumping into the 50s
and 60s. These temperatures seem cool, but are warmer than normal
for the end of November.

3) Phasing/Merging of the northern and southern stream lows will
combine Gulf moisture with very cold air to have rain changing over
to snow across the mountains Monday night. 850H temperatures drop
below 0C through the afternoon. However 1000-850 MB thickness
remains above 1300m into the early evening. This suggest the change-
over to snow will start in the higher elevations first. Lower
elevations may see snow starting to fall, but will melt on contact
through most of the evening, some of that is due to a warm ground.

4) The closed low over the Ohio Valley will slowly move to the
northeast Monday night into Tuesday night. With temperatures remain
at or below freezing, accumulating snow across the mountains will
occur through the period. Being under the deformation zone and
upslope longer than anyone else, western Greenbrier should see the
highest snowfall totals for Blacksburg CWA.

5) A 40kt low level westerly jet could bring gusty conditions to the
area Monday night into Tuesday. However, extensive cloud cover
should keep these gusts above 3000 ft. The stronger winds will occur
Tuesday night as pressure rises behind the departing low. Models are
also advertising a 50kt cross-barrier jet along the Blue Ridge.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 145 PM EST Friday...

The upper level low will be moving to the northeast Tuesday night
into Wednesday. Snow showers and windy conditions will eventually
give way to sunshine and warming temperatures Thursday. However,
rain returns to the region on Friday as warm air overruns another
surface wedge.

The coldest time in the period will be Wednesday morning with lows
in the 20s, wind chills values in the teens. The wind will subside
some on Wednesday but remain cold with highs in the 30s west of the
Blue Ridge to the 40s east. Temperatures moderate a few degrees each
day but remain colder than normal Thursday and Friday.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 620 PM EST Friday...

Expect VFR conditions east of the Blue Ridge through the valid period
under a cig of mid/high clouds. To the west, expect VFR through
early tonight. The a weak front will push some low level
moisture into the mountains late tonight with an MVFR cig
expected at KLWB and KBLF with hilltops obscured. Low clouds
will dissipate Saturday morning with VFR all sites expected
from Saturday afternoon through the end of the valid period.

Winds will generally be light with little impact to aircraft
operations, though some low end gusts may produce a light chop
later Saturday morning through the afternoon.

Extended Aviation Discussion...

VFR conditions persist til Sunday, then a much stronger system
with potentially multiple significant weather impacts is
expected to arrive early next week. Poor to very poor aviation
conditions expected Sunday night through early Tuesday, with
heavy rain, gusty winds, and possibly a thunderstorm or two
southeast of KDAN.

Colder air will rush in Monday night turning upslope rain to
snow showers in the mountains, with some gradual improvements
east of the Blue Ridge. Winds will begin to subside on
Wednesday.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...MBS/AMS
SHORT TERM...RCS
LONG TERM...RCS
AVIATION...MBS/AMS