Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 211712
Area Forecast Discussion
National Weather Service Blacksburg VA
112 PM EDT Sun Aug 21 2016
Scattered showers and thunderstorms today ahead of an approaching
cold front which will bring cooler and drier air to the region.
High pressure will dominate the weather until mid-week.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1255 PM EDT Sunday...
For this afternoon, a nearly solid line of showers will continue
heading eastward across the region. No thunderstorms have occurred
yet, but chances will increase as the activity moves into more
unstable air in the east. No major changes made to the ongoing
As of 1015 AM EDT Sunday...
Forecast update this morning will see its biggest changes across
the eastern portions of the area. Have removed the isolated to
chance POPs across this region of the area, especially across the
southeast portion of the area, until the early to middle
afternoon. This adjustment was based upon the latest radar and
guidance trends. Have also increased the high temperatures in this
area by a degree or two with the later arrival of notable
As of 345 AM EDT Sunday...
Upper trough will rotate across the Great Lakes today with
associated cold front pushing from the eastern Ohio Valley at midday
through to the Atlantic coast by early evening. Should see a period
of showers and possibly a few embedded thunderstorms ahead of and
along the boundary today with the best chances for rain in the west
and best chances for thunder in the east although will maintain some
thunder in the grids as MU Capes briefly reach 500-1500 J/kg from
west to east across the CWA in the 12-21z time frame across the
CWA per NCEP SREF. SPC maintaining marginal risk in the far
eastern counties with that higher CAPE and it may depend on the
amount of sun in that area. Best shear will be north of the RNK
CWA so any severe threat will be isolated. Rainfall amounts in
the 0.25 to 0.75 inch range today seem most probable as the front
will make fairly rapid progress with the strong upper support.
Rain should be tapering off by around 00z/22 with lingering
showers in the far east possible after that time. Don`t anticipate
any significant hydro issues with the speed of movement although
high PWATS ahead of the front will allow for some pockets of heavy
rainfall. After the front much drier air will work into the region
which may be a welcome change for some from the remarkably
persistent near tropical air mass of recent weeks. Should see
lows into upper 50s west to mid- 60s east by Monday morning, the
coolest we have seen since about one month ago. And actually those
temps are about normal for this date in August which shows how
long we have been above normal at night, over 30 days.
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.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
As of 330 AM EDT Sunday...
Dry cool air will filter into the region Monday as high pressure
will be centered over the Ohio Valley. With zonal flow aloft, this
high pressure system will drift east over the Appalachian Mountains
Monday night, then wedges down the Mid Atlantic on Tuesday. The
pattern remains progressive on Wednesday with the wedge center
moving off the New England Coast.
While this ridge is in the forecast area, temperatures will remain
cooler than normal with the mountains being in the 70s and areas
east of the Blue Ridge in the low to mid 80s. Humidity levels each
day will stay below 50% but will increase on Wednesday as winds
Also with a very dry air in the region, there will not be any
showers or thunderstorms in the area until late in the week.
.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
As of 345 PM EDT Saturday...
By Thursday, the surface high continues to drift off shore
allowing better return of Gulf moisture into the region. A broad
trough in the central U.S. will help drive a weak cold front
toward the region late Thursday with a better chance of convection
as a result west of the Blue Ridge. The front will continue to
move southeast Friday toward the NC Piedmont, then wash out as
high pressure aloft once again intensifies across the region.
Dynamics are weak both days, but scattered convection can be
expected, especially across the mountains, mainly west of the Blue
Ridge Thursday, then more to the east of the Blue Ridge across the
Piedmont on Friday.
Temperatures and humidity levels will be on the increase again
during this period as PWATS surge back toward the 2.0 inch mark
and 850mb temps creep back toward +20C.
The pattern established during the extended period opens the door
to potential tropical activity that may be looming the future.
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 700 AM EDT Sunday...
Scattered showers and isolated thunderstorms are expected today
as a cold front approaches the area. Main time window for
precipitation at the TAF sites will be 14z to 20z and the better
chances for a thunderstorm are in the afternoon at KDAN and
possibly KROA/KLYH . Potential for sub-VFR vsbys/cigs will persist
until the front clears the forecast area. Once the front moves
through after 00z/22 expect gusty northwest winds and a drying
trend. Mainly VFR will return for tonight with the exception of
morning fog at some TAF sites.
Extended aviation discussion...
Confidence is high for much drier weather across the region for
Monday through Wednesday as High pressure builds overhead,
promoting VFR. By Thursday, the center of the high will be far
enough east for western portions of the area to see a return of
isolated to scattered MVFR showers and a few thunderstorms.