Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 270108

Area Forecast Discussion
National Weather Service Blacksburg VA
908 PM EDT Fri Aug 26 2016

High pressure will be the dominant weather feature through the upcoming
weekend, with just a chance for an afternoon shower or thunderstorm
mainly along the Blue Ridge. A weak cold front may slowly slide
southward into the area by the middle of next week and continue the
chance for a shower or storm from the Blue Ridge westward.


As of 845 PM EDT Friday...

Isolated shallow convection over far northeast sections finally
fading out and should dissipate for the most part in the next hour
or two given loss of heating. Still could see an additional
isolated shower pop up elsewhere in spots between now and midnight
per leftover instability/outflow, otherwise leaving it dry overnight.
Guidance again showing some low level moisture under the inversion
aloft rounding the ridge into eastern sections late but this scenario
remains quite iffy. Think moisture more related to possible stratus/fog
development as parameters off soundings even better for fog tonight
so beefed up coverage by daybreak. Things remain very warm and muggy
even after sunset with some temps still in the 80s and dewpoints
in the 60s to mid 70s. Appears this will keep most eastern spots
from dropping out of the 70s overnight with mainly mid/upper 60s
mountains for lows.

Previous discussion as of 325 PM EDT Friday...

Expect any isolated showers or storms to dissipate this evening
followed by quiet weather for the overnight period. Another round of
valley fog looks like a good bet from the Blue Ridge westward toward
daybreak. Lows tonight look to be just a bit warmer than last night
with low/mid 70s in the east to low/mid 60s west.

Warm upper ridge will remain in place over the region through Saturday.
This will allow a large area of high pressure moving through eastern
Canada to wedge down the eastern seaboard tomorrow. This will push a
bit of a backdoor front into the area from the northeast and guidance
suggest this will provide enough lift in the warm and humid airmass for
a low chance for showers/thunder mainly for the southern Blue Ridge
heading into the northwest mountains of North Carolina. Highs tomorrow
will remain several degrees above normal with generally lower 90s east
and mid/upper 80s to the west.


As of 325 PM EDT Friday...

An upper level ridge will remain over the region through early next
week. Expect strong subsidence under this ridge, which will push
afternoon highs 5F-8F above normal with mid to upper 80s west and
lower to mid 90s east. At this time, heat indices values do not
approach triple digits, however with dew points in the upper 60s to
lower 70s, very uncomfortable conditions are expected the next
couple of days. Air quailty may be more of a danger, especially
those with respiratory problems as winds will remain light and
variable. Despite a strong ridge, diurnal heating and increasing
PWATS may allow for a few storms to develop over the mountains each
afternoon, but with almost no support aloft, any convection will be


As of 325 PM EDT Friday...

The upper level ridge over the region this weekend will retrograde
to the west and be replaced by an upper level trough. Embedded short
waves in this trough and a surface lee trough over the piedmont will
increase the chances for afternoon and evening showers and
thunderstorms. Areal showers may be moreso on Friday with a possible
front passage.

Models also continue to hint at a possible tropical disturbance in
the vicinity of Florida next weekend. However, with an upper level
trough along the east coast, the forecast track of this system
should stay south of the area.


As of 640 PM EDT Friday...

Isolated convection across the southern Shenandoah Valley and
northern Blue Ridge likely to persist with added cells popping up
mainly east of KLWB and north of the KROA-KLYH corridor in the
next hour or two before fading. Therefore leaving out any mention
in the tafs pending release coverage/proximity.

Otherwise high pressure to keep overall VFR in place overnight
through Saturday. A shallow boundary/backdoor front will make a
surge into the region from the northeast Saturday but do not
believe coverage will warrant any mention in the TAFs as
isolated/scattered convection will be centered on the southern
Blue Ridge and likely very late in the day. Thus, the biggest
concern will again be with low clouds/fog overnight given moist
dewpoints and light winds. Again appears the greatest likelihood
for MVFR/IFR conditions at KBCB with LIFR at KLWB. Guidance
continues to suggest additional cloud cover along/east of the Blue
Ridge late with trapped moisture under weak onshore flow. This
still looks overdone so will only include a mention of MVFR at
KDAN and KLYH toward daybreak. Lingering fog/stratus will burn off
Saturday morning with VFR conditions into early Saturday afternoon
under a scattered-broken 4-6 kft cumulus field.

Should see a repeat Saturday night with any lingering evening
convection fading after sunset followed by late night mainly
valley sub-VFR in fog/stratus.

Extended aviation discussion...

A weak front will remain over parts of the area Sunday. Isolated
to scattered diurnal showers and thunderstorms still possible into
Sunday evening. 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
VFR. Another front situated north of us Tuesday could enhance the
convective threat, mainly over the mountains and north of ROA/LYH.
Front should cross the region later Wednesday with possible sub-
VFR at times in pre-frontal convection Wednesday afternoon.




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