Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 170451

Area Forecast Discussion
National Weather Service Blacksburg VA
1151 PM EST Sat Dec 16 2017

High pressure will build across the Southeast U.S. tonight and
Sunday. Lows pressure over the Southern Plains will move
northeast toward the Ohio Valley and weaken tonight and Sunday.
Another low over the Southern Plains and lower Mississippi
Valley on Wednesday will move east through the end of the week.


As of 750 PM EST Saturday...

Very little change in going forecast, except to lower temps in
the mountain valleys and piedmont as skies stay mainly clear a
little longer allowing temps to drop a little faster. Thicker
high clouds arrive before dawn to stem the tumble temps. Still
looking at mainly lows in the mid to upper 20s, but a few deeper
valleys could drop to 20.

Previous valid discussion from early afternoon...

As we progress through the next 24 hours, the center of the
high pressure will move eastward to off the coast of the
Carolinas by Sunday afternoon. Anti-cyclonic flow on the west
side of the high will help advect milder temperature into the
area, as well as, help guide the developing low in the Gulf of
Mexico into the Deep South.

Associated moisture will start to stream into the area in the form
of high level cloudiness Sunday morning. By the afternoon, we expect
isolated to scattered showers to be across approximately the western
half of the region, with clouds continuing to lower an thicken
across the entire region.

On Sunday, despite increasing cloud cover, the influence of
increasing warming air advection should allow for high
temperatures a few degrees higher than those expected for today.
Anticipate mid to upper 40s across the mountains with low to
mid 50s across the Piedmont.


As of 210 PM EST Saturday...

Series of upper low will track out of Mexico and to the northeast
through the week. The first upper low weakens in the confluent zonal
500MB flow over the eastern United States,. What is left of this
short wave will cross over the Mid Atlantic region on Sunday night.
By then the next closed low will be over the Southwest. Models is
reasonable consensus on synoptic pattern and temperatures
through this time frame. 850MB temperatures will take longer to
warm up in eastern West Virginia, but even there by Tuesday will
be above zero. Persistent westerly flow and downsloping will
aide in warming temperatures in the foothills and piedmont
Monday and Tuesday.


As of 210 PM EST Saturday...

The second upper low also weakens as it moves northeast but takes a
more southern track through the Tennessee Valley. This short wave
crosses the Mid Atlantic region on Wednesday and Wednesday night. A
third upper low reaches the Southwest United States late in the week
with a larger spread in models solutions concerning location and
intensity. The main track of the vorticity maximums will depend on
the strength of the digging trof in the central United States
and the upper ridging over the Southeast. Models were showing a
spread of solutions for Thursday through Sunday.

In-situ type wedge of high pressure may develop over the area on
Thursday. Models keep the bulk of any precipitation south of
Virgina. Will keep better probability of precipitation mainly
on Friday night and Saturday.

Decent plunge of much colder air advertised by the GFS and
ECMWF on Friday and Saturday for the central and eastern United
States. Air mass will be cold enough to support snow in the
mountains on Saturday.


As of 1105 PM EST Saturday...

VFR conditions are expected during the extent of the valid TAF
forecasts, with mainly mid clouds increasing Sunday.

May start to see clouds lowering toward low end VFR in the
mountains Sunday evening with a few showers possible.

Extended Discussion...

A weak frontal system approaching from the west may induce a
brief period of MVFR with light rain showers across the
mountains through Sunday night. This may impact KBLF and KLWB.
VFR cloud bases anticipated elsewhere.

Little or no impact is expected to aviation for the central
Mid-Atlantic through mid week as weather features remain well
north and south of the geographic region. The greatest potential
will be Wednesday night, but even here, guidance is still not
consistent with its various solutions.




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