Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 300030

Area Forecast Discussion
National Weather Service Blacksburg VA
830 PM EDT Fri Jul 29 2016

Over the next several days, a series of disturbances will progress
across our region, near or along a stalled frontal boundary. This
interaction, along with the heating of the day, will continue to
provide us with a forecast that has chances of showers and storms in
it most days. Temperatures will be slightly above normal for this
time of the year.


As of 830 PM EDT Friday...

A shortwave trough along VA/NC Appalachian Divide continues to
progress east. Deep convection associated with this feature
has been moving east, but weakening. Per downslope westerly winds
east of the divide, expect this activity to continue to weaken
with mainly showers or isolated thundershower possible... the
highest pops across the NC high country.

On the backside of the shortwave, westerly winds will increase
enough to maintain upslope low level cloud cover across the
western portion of the area. Residual debris mid to high level
cloud cover associated with the system will cover much of the rest
of the skies across the area through Saturday morning. Low
temperatures tonight will be comparable to those realized this
morning. Expect low to mid 60s across the mountains with readings
around 70 to the lower 70s across the Piedmont.

On Saturday, yet another upper level disturbance will impact our
region. The trajectory for this one will take a generous portion of
it north of our area. However, enough of it will bring another round
of scattered showers and storms to the area, especially in the
afternoon. Coverage will be greatest across the northern third of
the region. The Storm Prediction Center has updated its Day 2
Convective Outlook to include a marginal risk of severe weather
across those areas of the forecast area generally along and north of
the Roanoke River, east of Roanoke, VA. High temperatures tomorrow
will range from the low to mid 80s across the mountains to the upper
80s to around 90 across the Piedmont.


As of 300 PM EDT Friday...

Mid-summer type pattern continues across the CONUS with main belt of
the westerlies north of the Mid-Atlantic region. Low amplitude
troughing develops across the eastern half of the U.S. with energy
topping the mean western U.S. ridge and dropping southeast into the
trough position. A fairly well-defined short-wave is currently
forecast by model consensus to be lifting northeast toward New
England Saturday night with the best chances for organized rainfall
tracking along with it. Lingering showers and few storms are
possible Saturday evening with slow clearing toward Sunday morning.
Sunday looks to be somewhat drier as slightly drier dewpoints are
forecast to filter into the region. The change will be subtle but
perhaps noticeable as guidance shows mid-60s dewpoints across the
mountains by Sunday morning compared to the upper 60s and low 70s of
recent days. Highs Sunday will range from mid- to upper 80s
mountains to low 90s piedmont with dewpoints drifting upward into
upper 60s to low still muggy. Scattered showers and
thunderstorms again possible in the afternoon under diurnal
heating and localized convergence but coverage should be less than
on Saturday. Will maintain 30-40 pops in Sunday afternoon across
most of the area during favored peak heating hours and diminishing
as usual overnight.

Slight cooling Monday as the frontal boundary slips to our south
becoming stationary over the Carolina and h85 temps drop a few
degrees into the 16-18C range from 18-20C on Sunday. Should yield
highs mid-80s to low 90s with some low 80s possible far west. Still
chances for scattered diurnal thunderstorms generally 20s and 30s
pops with highest over the mountains due to differential heating.


As of 300 PM EST Friday...

Extended range models (GFS/Euro) show upper trough over the
northeast slowly lifting out on Tuesday with surface high pressure
in control and generally dry conditions. Significant exception is
12z Canadian model which brings a strong short-wave across the
central Appalachians late Monday into Tuesday with high chances
for rainfall. Elected to discount that solution for now and go
mostly dry on Tuesday with slightly lower humidity, could even see
a few dewpoints under 60F in the western mountains and under 70F
east, which may actually be noticeable. Temps generally seasonable
for early August. Front drifts back toward the north on Wednesday
with increasing pops and and humidity as heights begin to build
aloft once again. With upper ridge and rising heights continuing
to shift eastward Thursday and Friday should see warmer temps and
higher humidities again with renewed pattern of scattered
afternoon storms but nothing particularly organized.


As of 800 PM EDT Friday...

A mix of MVFR and VFR ceilings can be expected overnight as a weak
upper level shortwave ripples across the central appalachians.
Scattered showers and/or isolated thunderstorm is possible mainly
west of Blue Ridge.

In the wake of the disturbance, a westerly flow will help
maintain upslope IFR/MVFR ceilings along the west side of the
Appalachians, impacting BLF/LWB. This low cloud layer is expected
to lift to VFR by 14Z/10AM on Saturday. Patchy light IFR/MVFR fog
is also possible late tonight into early Saturday morning for
parts of the region.

Extended aviation discussion...

The region will remain in an active weather pattern into early
next week. A nearly stationary frontal boundary will be across or
near the region, all while a series of upper level disturbances
moves along this feature through the area. By Wednesday the front
may move south of the region enough to take the focus for
additional showers and storms with it. VFR conditions are expected
for most of the time. The exception will be temporary sub-VFR
conditions under the heavier showers or thunderstorms, and during
the night with patchy light fog and stratus cloud development over
parts of the region.




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