Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 190714
Area Forecast Discussion
National Weather Service Blacksburg VA
314 AM EDT Wed Apr 19 2017
-- Changed Discussion --High pressure weakens into Wednesday night. A cold front will
then approach from the west later in the week, stall and bring a
chance for showers and thunderstorms Thursday into Saturday.
-- End Changed Discussion --
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 300 AM EDT Wednesday...
Nose of high pressure stays wedged east of the Appalachians today,
with increasing moisture/lift over the 300K Theta Surface as we head
through the morning. The overall scheme favors mainly light to at
times moderate rain. Will not see it raining all day but most folks
will have rain at some point, with most receiving around a tenth of
an inch with locally higher to one half inch possible toward the
mountains of Southwest VA if thunderstorms occur. SPC has general
thunder as far east as Greenbrier to Mt Rogers. Limited instability
due to cloud cover will keep thunder chances isolated at best.
The surface high and subsequent wedge weaken by this evening but
expect cloudiness and light rain to linger in spotty fashion into
this evening, then some drying to the east of the mountains after
midnight, as flow starts to turn more southwest to west in the
low/mid levels. Fog may become an issue late tonight if we get any
clearing but overall models showing cloudiness around through the
period with some breaks at times, so fog will be patchy.
Highs today factored toward cooler mos in the wedge with mid to
upper 50s from Greenbrier to the New River Valley east to the
piedmont north of Danville/South Boston. Warmer air will stay
southwest of a BKW-MKJ line with mid to upper 60s expected.
Tonight the airmass remains moist so lows should stay elevated in
the upper 40s to mid 50s.
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.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 345 PM EDT Tuesday...
Increasing southwest wind flow ahead of an approaching front
from the Ohio Valley will bring warming temperatures and partial
clearing for Thursday. Can`t rule out a stray pop-up shower or
thundershower Thursday, but think day as a whole will be dry
with primary focus for showers residing along the front which
will be over the Ohio Valley.
Better threat for showers will accompany the front as it enters
the CWA late Thursday night, crossing the forecast area Friday.
Forward progress of the front is expected to slow as main area
of upper support passes from the Great Lakes into Ontario then
exits to the northeast across New England. This will leave us in
a situation where the front will either stall over or just south
of the VA/NC border Friday night.
With front stalled across the Mid-Atlantic, this will set the
stage for a wet weekend, models indicating a strong area of low
pressure developing over the central Plains and moving east
along the front.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 415 PM EDT Tuesday...
An area of low pressure is forecast to move east along a stalled
front which will be aligned east west from the Mid-Atlantic
Coast to the central plains. The low will cross the Mid-MS
valley Saturday, then directly across the Mid-Atlantic Region
Sunday. Primary focus for wetting rain will be along the stalled
front with increasing southwest wind flow aloft over-running the
front. Dynamic lift will also increase, especially Sunday as the
area of low pressure passes overhead, yielding 2 day rain
amounts (Saturday-Sunday) of 1-2 inches, with isolated higher
amounts possible pending thunderstorm development.
High pressure will build into the area Monday into Tuesday, dry
weather returning for the middle of next week.
Maximum temperatures will average near to slightly below normal
this weekend thanks to abundant cloud cover, and the forecast
area residing on the cool side of the front. A transition to
warmer than normal temperatures will return by the middle of
next week after a couple of near normal days Monday and Tuesday.
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
As of 123 AM EDT Wednesday...
Expect mainly MVFR cigs this period but at times, will see VFR
early before low levels moisten up more. High pressure pushing
southwest to the piedmont this morning and increasing rain will
continue to bring cloud bases lower, and should see some IFR to
possible LIFR at times along/east of a LWB-HLX line. Rain will
be mainly light keeping vsbys above 5sm, though some periods of
moderate rain and patchy fog could drop it to MVFR.
Question later today will be the erosion of wedge and how high
cigs get. Appears models keep the damming in place at all but
BLF but also insist on high end MVFR to low end VFR taking
shape, then going more VFR Wednesday evening. Confidence is low
in this but will trend toward VFR after 00z Thu.
Extended Aviation Discussion...
By Thursday, the front will return north as a warm front just
as a new front approaches from the northwest. Showers and
thunderstorms will be on the increase Thu-Fri as this front also
drifts into the area and then stalls Friday just south of the
CWA, most likely near the NC/SC border. This front will return
to the north as a warm front Saturday as a much stronger weather
system moves into the southeast U.S. While there may be some
periods of VFR cigs Thursday as the area comes into the warm
sector, expect MVFR or worse ceilings to return at times Fri-
Sat, with widespread sub-VFR ceilings Sunday with widespread
heavy rainfall and some storms in the KDAN area during the
afternoon Sunday. Winds may be a factor late in the weekend as