Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 162308

Area Forecast Discussion
National Weather Service Blacksburg VA
608 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 230 PM EST Saturday...

Surface high pressure was centered over central Alabama. A cold
front extended west to east from southern Minnesota into New
England. A trough of low pressure was deepening into an area of low
pressure in the western portion of the Gulf of Mexico. As we
progress through the next 24 hours, the center of the the high
pressure will move eastward to off the coast of the Carolinas by
this time Sunday. 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.

Lows tonight will reflect the scenario of the the higher elevations
remaining mixed within the stronger breezes aloft, and thus milder
than their neighboring valleys. Likewise, the Piedmont region will
also remain cooler than the higher terrain to the west. Lows tonight
will fall into the mid to upper 20s across most locations. The
higher ridge tops will be milder with lows in the lower 30s.

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


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 cold enough to support snow in the
mountains on Saturday.


As of 605 PM EST Saturday...

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

Extended Discussion...

A weak frontal system approaching from the west may induce a
brief period of MVFR with light rain showers across the
mountains 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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