Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201143

Area Forecast Discussion
National Weather Service Blacksburg VA
643 AM EST Fri Jan 20 2017

A warm front will bring a period of rain early today before
dissipating this afternoon and evening. A small period of dry
weather occurs tonight then a frontal boundary situated across
the Gulf Coast states starts to increase the moisture and
rainfall again by Saturday night into Sunday. The low with this
system will move to Virginia by Monday.


As Of 620 AM EST Friday...

Latest RAP model showing the best solution to radar/obs at 11z.
Should see batch of rain move east to the piedmont by 9am, with
lingering light rain/drizzle in the mountains. Still on track to
dry out this afternoon.

Previous discussion from early morning...

Overall seeing a little slower onset of rain this morning per lack
of echoes on radar and surface observations mainly showing mid deck
clouds. For the rest of the early morning leaned toward the high-res
models show slower timing but still looks like it will be wet
morning commute for most of the region.

Best lift passes across between 10z-15z, then shifts to the mid-
Atlantic this afternoon. Warm front lingers south of us this
afternoon so question is will any clearing take place? The
downscaled NAM and Canadian as well as the HiRes-ARW showing some
clearing across portions of southern VA into NC while the GFS hangs
in the lower clouds longer. Think some breaks possible but overall
staying mostly cloudy with patchy drizzle may occur as the rain
pulls out early in the afternoon. Tricky temperature forecast given
rainy morning followed by dry afternoon but lingering cloud cover.
Will go a degree or two under guidance especially from the
Greenbrier Valley south to the NC foothills and east, with readings
in the 50s. Appears enough clearing and earlier exit of rain will
allow temperatures to reach the lower 60s over southern WV into the
Mountain Empire of Southwest VA.

Tonight weak southerly flow with dissipating warm frontal boundary
may set up a fog and low clouds scenario, especially in the
foothills/piedmont. Guidance actually advertising dense fog in some
locations, but cloud cover may limit this. Should be mainly dry with
lows in the 40s.


As of 215 AM EST Friday...

A wet and very mild period is expected during this portion of the
forecast. A broad upper trough will be positioned from the Four-
Corners region north to the Dakotas. Southwest flow in advance of
this trough will bring Gulf of Mexico moisture and leading weak
disturbances into and through the region.  Anticipate rain showers
to overspread the area from southwest to northeast starting slowly
at first on Saturday, but growing in coverage and intensity Saturday
night and continuing into Sunday.

By Sunday evening, the main upper low is expected to have progressed
eastward from the Four-Corners region to the lower Mississippi
Valley region. The leading shortwave trough is expected to have
lifted closer to the Mason-Dixon line, allowing for a decline in
coverage Sunday evening. This break will be short lived as the upper
low continues its progress eastward into either the Deep South or
the Tennessee Valley. Either location will allow for the
deformation on zone on the north side of the low to become situated
over the area, and then slowly pivot as the low makes a swing
northeast closer to the VA/NC/SC coast by Monday evening.

By Monday night, the low is expected to be near, or north of the
Delmarva Peninsula with flow across our region increasing from the
northwest. Expect winds to become gusty Monday night with colder air
moving into the region. Precipitation will continue in the west
thanks to upslope flow and residual low level moisture. Enough cold
air may reach the higher terrain of southeast West Virginia by
daybreak Tuesday for some isolated snow showers in western
Greenbrier County.

Precipitation during event will be plentiful.  Total amounts may be
near two inches near the NC/VA border east of the crest of the Blue
Ridge. Lesser amounts are expected the farther northwest one is from
this location with an average of three-quarters of an inch across
southeast West Virginia. If these amounts are realized, the
potential will increase for minor flooding, especially across the
southeast portion of the region.

Increased surface based instability is also expected during this
event, especially Sunday afternoon. The far westerns parts of the
area, as well as, the far southern and southeastern sections may
experience some isolated thunder.

Temperatures will continue to be very mild during this part of the
forecast. Temperatures will start the period off around twenty
degrees above normal on Saturday and decline to readings still some
five to ten degrees above normal on Monday.


As of 200 PM EDT Thursday

Once the surface low is off the coast on Tuesday, precipitation
will be confined to favored western upslope areas. Winds will
also increase Tuesday. There may be enough of a low level jet
along with cold air advection and pressure rises for wind gusts
in the 40 to 50 mph range.

By Wednesday and Thursday a long wave positively tilted upper trof
will extend from the Great Lakes across the central United States.
Prevailing deep southwest flow over the Mid Atlantic region
during this time frame results in differences among the models
in how fast any front will progress east. For now WPC has
surface front crossing the region Wednesday and Wednesday
night. Behind this system is a much colder air mass. More
upslope snow showers in the mountains are possible. At this time
the models are showing snow showers for Thursday night.


As of 630 AM EST Friday...

Overall looking at MVFR to occasionally IFR conditions this
morning with rain. Will see the area of rain move east and out
of the region by 19z. During this time will see some improvement
to VFR with some lingering MVFR in the piedmont.

Tonight, will see cigs start to lower once again. Big question
is fog development with some models favoring dense fog at
BCB/LYH and possibly LWB/DAN, though coverage of clouds will
inhibit some fog, so did not go with a lot.

Extended Aviation Discussion...

Southwest flow aloft will persist ahead of a deep upper low
that will develop across the southeast states over the weekend,
then move off the southeast U.S. coast Monday. This pattern will
likely keep terminals in sub-VFR during a majority of the Sat-
Mon period. An additional wave of rain moving into the area
late Saturday and persisting into Monday. Post storm system
winds pickup some Tuesday. Ceilings and visibilities should
finally improve east of the Blue Ridge after Tuesday, but likely
persist with MVFR and upslope flow west of the Blue Ridge.


As of 305 PM EST Thursday...

Record warm Mins for January 21

Blacksburg....42 in 1954
Bluefield.....47 in 1999
Danville......56 in 1954
Lynchburg.....51 in 1927
Roanoke.......51 in 1959

Record highs for January 21

Blacksburg....59 in 1954
Bluefield.....60 in 1999
Danville......68 in 1959
Lynchburg.....72 in 1932
Roanoke.......74 in 1932




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