Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 261127

Area Forecast Discussion
National Weather Service Blacksburg VA
727 AM EDT Wed Jul 26 2017

High pressure over New York will be wedging southward over us
today. The high moves southeast off the Delmarva tonight. A
front will approach from the northwest Thursday afternoon,
sliding across our area Friday afternoon into Friday night.


As of 715 AM EDT Wednesday...

Update to forecast includes increasing cloud cover as low clouds
have spread all the way into southeast WV per easterly fetch.
Should see skies scatter out by midday/early afternoon under
late July sunshine.

Previous discussion from early morning...

Overall seeing more low level moisture/clouds than most models
predicted this morning, with latest surface analysis showing a
decent easterly fetch in the pressure gradient over the Blue Ridge
and points east while surface winds have amped up a bit in places
like Mount Airy, NC out of the northeast. Have bumped up cloud cover
to account for this.

As far as today goes, showers should be isolated to widely scattered
and confined to the Blue Ridge generally south of Blacksburg-Floyd,
VA with best coverage across the Boone area and south with better
low level moisture convergence and deeper moisture.

Overall still looking at skies becoming mostly sunny across much of
by late morning with scattered to broken cumulus this afternoon.
With an easterly to southeast wind, temperatures should below normal
for highs today, ranging from the mid 70s in the NC high country and
higher terrain of Virginia, with upper 70s to lower 80s in the
valleys, to mid 80s in the piedmont/foothills.

Tonight, surface high shifts southeast and winds turn more south to
southwest allowing dewpoints to creep back up. Limited showers in
the southern Blue Ridge should fade by late evening. With flow more
southerly should see less upslope induced stratus, though some of
the models still indicating potential for stratus/stratocu along the
Blue Ridge into the piedmont.

Lows tonight will be in the mid to upper 60s across most areas, with
patchy fog possible in the mountain valleys.


As of 300 AM EDT Tuesday...

High pressure will weaken and slide east into the Atlantic ocean
Thursday, as a cold front approaches from the west. The eastward
progress of the frontal boundary will be slowed by the zonal flow
aloft. The cold front should reach the mountains Thursday night into
early Friday morning, then move east of the Blue Ridge Friday
afternoon as an upper level low tracks across the Great Lakes into
the Mid Atlantic region by Friday night.

As the larger scale mid level trough deepens and expands Thursday,
the combination of diurnal heating, low level convergence and
orographical lift should generate scattered showers and
thunderstorms across the mountains early Thursday afternoon.
This convection will slowly drift eastward Thursday evening and
Thursday night. SPC in the day 2 convective outlook continues to
have much of the forecast area in a slight risk for severe
thunderstorms. The primary threat is the potential for damaging
winds and heavy rains. There remains some uncertainty on the
coverage and potential of severe weather with NAM, GFS and ECMWF
showing different solutions and timing. Differences abound with
respect to amount, intensity, location of convection associated with
this lead trough. The potential for severe weather is dependent on
amount of instability (best instability north of us) and development
of Ohio Valley Convection. Details will become clearer with time.
High temperatures will be slightly warmer than normal Thursday with
low to mid 80s expected west of the Blue Ridge and upper 80s to
lower 90s in the east.

Linger instabilities and a 30-40 knot low level jet could allow some
strong storms to pass over the area Thursday night into Friday
morning. Low temperatures Thursday night will range from the lower
60s in the mountains to the lower 70s in the piedmont.

Showers and thunderstorms will spread east on Friday and reach the
Piedmont by Friday night. The best dynamics with this front will
remain north of our area over Pennsylvania and Maryland and move to
along the New England coast Friday. However, scattered strong to
severe thunderstorms may be possible across the foothills and the
Piedmont. This is where the gfs and ecmwf paint the best helicity,
capes and sfc computed lis. SPC Day 3 has a marginal to slight
across our forecast area for Friday with the potential for organized
fast-moving bands of storms. The main questions at this time revolve
around timing of synoptic features.

The severe potential could increase if the front is slower placing
frontal passage during peaking heating Friday afternoon. Cloud cover
and convection will result in cooler highs for Friday with readings
from around 70 degrees in the western mountains to the mid 80s in
the piedmont. By Midnight, thunderstorms should taper off leaving
just lingering showers Friday night. Low temperatures Friday night
into saturday morning will generally range from the upper 50s in the
western mountains to the upper 60s in the piedmont.


As of 300 AM EDT Wednesday...

The upper level trough will be overhead Saturday and move east
Saturday night into Sunday. Heating under this cold pool may result
in scattered diurnal showers to the region Saturday afternoon. High
temperatures will be cooler than normal with reading from around 70
degrees in the mountains to the mid 80s in the piedmont. Surface
high pressure will build southeast over the region Sunday. The high
center will slide east into Midweek. This ridge of high pressure
will keep the area cool and dry.


As of 724 AM EDT Wednesday...

Low clouds and MVFR cigs worked all the way into WV this morning
per a tighter gradient allowing for more upslope and easterly
fetch of Atlantic moisture.

Should see cigs start to lift to VFR and scatter out some by
midday with BCB the last to go above MVFR at 18z.

Should be mainly a VFR forecast, through tonight, Exception
will be LWB fog still a possibility so not going any lower than
3sm, as another day of drying wx should limit fog.

Aviation Extended Discussion...

Should start to see a front approaching with better threat of
showers/thunderstorms Thursday into Friday. Stronger storms and
heavy rain possible in and around the mid-Atlantic/Ohio Valley
region into the Carolinas this time frame so be prepared for
sub-VFR at times. Outside of storms expect VFR conditions, with
possible late night fog by Friday morning.

Saturday looks drier with northwest flow, but could see
lingering low end VFR/high end MVFR ceilings in SE WV along with
a few added shra/tsra mainly southern sections Saturday
afternoon. Expect widespread VFR to return Sunday under high
pressure following the front.




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