Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 251137

Area Forecast Discussion
National Weather Service Blacksburg VA
737 AM EDT Thu Aug 25 2016

High pressure over the region shifts slowly east today into tonight.
The upper ridge will remain overhead through the end of the week.


As of 300 AM EDT Thursday...

High to mid clouds from the Ohio Valley convection will continue to
spread eastward across the region this morning. The combination of
low level moisture and light winds has resulted in patches of low
clouds and fog this morning. These low clouds and fog will lift by
mid to late morning.

The center of the upper high slides across the Appalachians and
Tennessee Valley this afternoon into tonight. Building heights aloft
will keep most showers and thunderstorms limited. The day one
convective outlook places our area in general thunderstorms with
slight risk of severe to our northwest in the Ohio Valley and Great
Lakes Region. A weak shortwave rotating through the region could
generate a few morning showers in the northwest mountains, then
isolated to scattered showers and thunderstorms may develop this
afternoon across the higher terrain. High temperatures this
afternoon will range from the upper 70s in the mountains to the
lower 90s in the Piedmont. Heat index values are expected to remain
below heat advisory criteria this afternoon. Any convection will
diminish quickly this evening with loss of heating, leaving clear to
partly cloudy skies tonight. With light winds, patchy of low clouds
and fog will develop tonight into Friday morning especially in the
valleys. Low temperatures tonight will vary from the lower 60s in
the west to around 70 degrees in the east.


As of 430 AM EDT Thursday...

The main story through the period will continue to be a strong
subtropical ridge that will drift from the Midsouth into our
region by the weekend. The weak front that will move into the
area today will drift slowly south into the Carolinas and
basically wash out by the weekend. Heat, moisture, and instability
are certainly sufficient for diurnally driven showers and
thunderstorms, but upper-level forcing/dynamics are nil under the
strong upper ridge. Most models indicating a scattering of
convection/qpf across the region focused near the dissipating
frontal boundary or more notably across the northwest NC
mountains. Thus, have focused slight chance to low chance pops in
these areas. Over the weekend, the front will continue to
dissipate to our south/southwest as a new similar front moves into
the region by Sunday. Have continued advertising diurnal slight
chance to low chance pops mainly western mountains areas through
the period. With weak dynamics and very little forcing, the severe
threat is little to none with manily pulse thunderstorms. Duration
should be limited, so heavy rain should also not be a problem.

Temperatures will average well above normal through the period.
Expect a fairly good jump in maximum temperatures between today
and Friday as 850mb temps surge into the +20C to potentially as
high as +24C (per GFS) range Friday. This will yield maximum
temperatures in the lower to mid 90s across the Piedmont and well
into the 80s elsewhere. These readings are a good 10 degrees above
normal. Minimum temperatures will also be on the increase through
the period as dewpoints/RH values continue to increase toward 70F.
Look for lows to average a good 10 degrees above normal as well
into the weekend with 60s mountains to lower 70s Piedmont.


As of 450 AM EDT Thursday...

The upper-level ridge will begin to weaken as we progress into the
mid part of next week but will also be the key to steering a
tropical system that is forecast by most models to track into
south Florida early in the week. Although the track is now
relatively similar among the models, there are vast differences in
the intensity. While the GFS shows a weak tropical low drifting
slowly north to northeast across FL into southeast GA and
eventually the Carolinas through the week, the ECMWF develops a
tropical storm/hurricane, which it similarly moves northeast,
albeit much quicker than the weaker GFS system. Meanwhile, as the
upper high weakens and shifts south of our area, another weak
front is progged to drift into the region by midweek. Much of the
time, our region will likely remained sandwiched in between the
frontal precipitation to our north/west and the tropical system to
our south. However during the later part of the week, the tropical
system could begin to impact at least the southeastern parts of
our CWA and with the pattern in place, there is always at least
some concern of a predecessor rain event. At any rate, considerably
uncertainty remains and such considerations still remain just
beyond this forecast period. Therefore, will continue the trend
established in the short term period of slight chance to low
chance diurnally driven pops and well above normal temperatures
moderating only slightly closer to normal by the end of the period
as cloud cover and moisture increase, the upper high weakens, and
850mb temps drop back a few degrees.


As of 730 AM EDT Thursday...

VFR conditions will prevail through most of the TAF valid period
as high pressure both surface and aloft moves slowly east across
the region. The main exception to VFR conditions will be patchy
dense fog and localized IFR-LIFR vsbys/cigs through 13/14Z this
morning at the usual spots, namely KLWB and KBCB and again after
07Z Fri morning. Otherwise, extensive mid/high clouds will spread
across the region again today in association with a weak cold
front that will drift from northwest to southeast across the area.
The associated cloud bases are expected to 035 to 050, namely VFR.
An isolated -shra cannot be completely ruled out as activity is
drifting southeast along the front from WV. However,
forcing/dynamics are very weak under the upper high. The front
will drift south of the area by Fri morning leaving the region
with just scattered mid cloud/high clouds and again the potential
for patchy fog late tonight. Winds are expected to veer more to
the west today at speeds of 4-7kts, becoming calm most areas after

Medium to high confidence in cigs through the TAF valid period.
Medium to high confidence in vsbys through the TAF valid period.
Medium to high confidence in wind speed/direction through the TAF
valid period.

Extended aviation discussion...

Storms will again be isolated and mainly confined to the mountains
on Friday as upper ridging strengthens, while a weak surface front
stalls to the south. Brief MVFR conditions could occur where any
convection does develop but appears mainly VFR given spotty nature
to any showers.

The front washes out during the weekend, but another weak front
will drift into the area Sunday. Isolated to scattered diurnal
showers and thunderstorms still possible each day. Coverage will
be limited in area and duration.

Monday high pressure bubbles in but still a very humid airmass to
keep isolated mountain storms around in the afternoon, but mainly




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