Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 260508
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
108 AM EDT Tue Jul 26 2016

.SYNOPSIS...
Lingering strong high pressure aloft over the Carolinas will
result in hot and humid weather into at least mid week. A weak
frontal boundary just north of the region should also continue to
oscillate across the Mid-Atlantic region through the end of the
week. Weak impulses riding along the front will combine with deep
moisture to produce periodic rounds of showers and thunderstorms
each day.
&&

.NEAR TERM /THROUGH TODAY/...
AS of 1000 PM Monday...

Heat Advisory in effect from noon to 8 pm EDT Tuesday for South
Central Piedmont of Virginia.

Widely scattered thunderstorms have been mainly confined to areas
along and west of the Blue Ridge with forcing over the mountains
providing just enough lift to trigger storm activity. Can`t rule
out additional activity during the overnight, esp western slopes
of the Appalachian Divide (Mt Rogers vicinity) where light
westerly flow will continue to provide for weak low level
convergence during the overnight. Overall intensity however,
should wane per loss of daytime heating.

Upper ridge will slowly weaken or flatten tonight into Tuesday as
shortwave troughing passes to the north. Surface boundary sinks
southward to just north of the area late tonight into Tuesday with
the axis of higher pwats and weak lift strung out from the western
slopes to across the north. This may result in convection linger
especially across the north tonight. Otherwise, partly to mostly
cloudy and very muggy expected tonight. Low temperatures tonight
will range from the mid 60s in the mountains to the mid 70s in the
Piedmont.

The frontal boundary will drop south across our region on Tuesday.
The combination of frontal ascent, orographic lift, and heating will
result in scattered showers and thunderstorms especially during the
afternoon. SPC in day two convection has portions of forecast area
in marginal risk for damaging winds with convective clusters. High
temperatures on Tuesday will range from the lower 80s in the
mountains to the mid 90s in the Piedmont. Heat indices will climb
as high as 105 degrees in the far east.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
As of 300 PM EDT Monday...

The upper level ridge will continue to sink south across the
southeastern US through Thursday. Lowering heights means
temperatures will be a little bit cooler each day. However,
temperatures will remain above normal until we can get a cold front
to pass over the region. Unfortunately, there is no frontal passages
expected this week. Afternoon temperatures will run around 5F warmer
than normal with 80s across the mountains and low to mid 90s east.
Dew points will also remain elevated ranging from the mid 60s to
lower 70s. Heat indices values will run 5F-8F warmer than the actual
temperature.

Some heat relief will come in the form of showers and thunderstorms
each afternoon. Even though these storms may knock temperatures
down, they will increase dew points keeping conditions very
uncomfortable. The coverage of storms will increase each day and
start earlier and end later. With zonal flow aloft, storms will
start across the mountains by noon, then drift east over the
piedmont during the evening hours. Forcing both Wednesday and
Thursday is not ideal for widespread strong storms, however with
zonal flow aloft, any waves rounding the ridge could change that.
For now, we will continue to see a typical summer pattern with
scattered afternoon and evening pulse storms.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 215 PM EDT Monday...

The ridge of high pressure will drift off the southeast coast
Friday, allowing an upper level trough to move over the Ohio and
Tennessee Valleys Friday. Models develop a surface reflection along
a lee trough that will bring an increase chance for strong to
severe storms into the region. Models currently are placing the
stronger dynamics Friday north of DC, but with all the
instabilities, heat and moisture in the region, the chance for
widespread severe weather will increase for the area Friday and/or
Saturday. If we do not see widespread significant weather Friday,
then Saturday will be the day. The upper level trough over the Ohio
Valley strengthens Saturday and will push bulk of the energy east to
the coast on Sunday. The upper level trough remains to our west
Sunday and Monday, which keeps the chance for showers and
thunderstorms in the area.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 1250 AM EDT Tuesday...

Earlier convection has about faded out tonight resulting in
widespread debris mid/high cloud canopy over some patchy strato-cu
across the south. Given the current soupy conditions and lingering
instability, cant totally rule out added isolated convection
through daybreak but not enough to include mention attm. Otherwise
mainly VFR expected aside from some river valley fog or shallow
ground fog for areas which received rain Monday evening. Again
appears that KLWB will drop down to a period of IFR/LIFR but less
confidence than usual given degree of mid clouds around and more
tropical nature conditions. Elsewhere could also see IFR at KBCB
and MVFR at KDAN/KLYH right before daybreak. Any fog or stratus
that does form will quickly disperse after sunrise.

Given strong instability would expect greater coverage of storms
Tuesday afternoon compared to the widely scattered activity
Monday. However models continue to vary on expanse and locations
of coverage as ridging aloft appears stronger than earlier
forecast, while focus on residual outflow...southeast lee trough
and upstream pre-frontal zone could lend to multiple clusters in
spots Tuesday afternoon. For now will continue trend in including
a VCTS mention most locations and attempt to refine spots Tuesday
morning that have the best chance of seeing sub-VFR in convection
in the afternoon.

Otherwise mainly VFR with cu buildups expected Tuesday afternoon
ahead of convection before again giving way to debris clouds and
patchy fog Tuesday night.

Extended aviation discussion...

Little change in the overall scenario can be expected Wednesday
through Saturday at this point with the upper ridge remaining just
south of the area and a residual front nearby. This should allow
for periodic daily convective coverage through much of the period.
Appears more widespread sub-VFR possible in convection per a
stronger wave along the front later Thursday with perhaps some
decrease in coverage by the weekend as this feature passes.
However given uncertainty appears at least diurnal MVFR/IFR
possible each afternoon/evening through Saturday for now. Late
night and early morning fog will likely occur at the usual valley
locations, and those chances increase across the entire region if
any rain occurs during the afternoon or evening at any site.

&&

.CLIMATE...
Record high temperatures for Tuesday (7/26)

Roanoke.....101 in 1930
Lynchburg...104 in 1934
Danville.....99 in 2012
Blacksburg...94 in 1987
Bluefield....91 in 1993

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Heat Advisory from noon today to 8 PM EDT this evening for
     VAZ046-047-058-059.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH/RCS
NEAR TERM...KK/PM
SHORT TERM...RCS
LONG TERM...RCS
AVIATION...JH/PM
CLIMATE...PM


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