Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1107 PM EDT Thursday Aug 28 2014
a weak cold front will stall across North Carolina late tonight...
then head back north again for Friday into Saturday. A stronger
upper system will bring a better threat for showers and storms to
close out the Labor Day weekend.
Near term /through Friday/...
as of 1100 PM EDT Thursday...
Backdoor front currently hung up over Southside Virginia and northwest NC...along
a ukf-mwk-mtv-lyh-fvx line. Dewpoints along and south of the front
are in the lower 70s. North of the front dewpoints were in the
upper 50s to lower 60s. Front not expected to make much progress
overnight...may drift to along the Virginia/NC border or just into
northern NC. There has been an ongoing cluster of rain showers/thunderstorms and rain near
Buckingham and Farmville vicinity of the frontal boundary...radar
estimating upwards of an inch of rain falling over parts of
southern Buckingham County during the evening. The hrrr model
shows a gradual drift of this precipitation toward I-95 cooridor during
the overnight with potential redevelopment of rain showers vicinity of the
front from Charlotte Court House east during the overnight.
Aside for the shower threat along the front...not much going on
weatherwise. The northern/western County Warning Area...from the NC mountains into the
nrv of Virginia...and from the the Greenbrier valley of WV east along
the I-64 corridor into central Virginia will reside north of the front
overnight. With dewpoints in the 50s...temperatures should be
about 10 degrees cooler than folks south of the frontal boundary
where readings will be closer to 70.
Overnight...some of the models...especially the NAM...indicate increasing
low level cloud cover per development of easterly low level winds
vicinity of the front...the resultant upslope flow into the Blue
Ridge resulting in cloud development late tonight. At this time will
continue to advertise some stratus in the morning...but prefer to
keep overall sky conditions toned down from the NAM but think
areas over the foothills and Piedmont could be mostly cloudy in
the morning. Patchy fog will form in the mountain valleys late
tonight where skies should stay mostly clear...partly cloudy at
worst. Lows tonight will be a little cooler in the north per drier
air with readings in the middle to upper 50s...while temperatures
will be closer to the 65-70 degree rang in the south.
Friday...front starts working back north across US. Models are
agreement that lift and moisture will be limited over US but cannot
rule out isolated rain showers/thunderstorms and rain in the region. Best lift will be across
the SW Virginia Mountains toward Tennessee...so have 30ish probability of precipitation here. Another area is
over the Raleigh-Durham area and east...so may see some scattered
storms toward Yanceyville. Southeast winds will be keeping temperatures from
getting too high...plus dealing with potential low clouds into
morning over the east. Highs will may work out to be homogeneous
across the entire County Warning Area outside the higher elevations with lower to
middle 80s. Southeast flow downslope warming may increase temperatures over the mountain
Empire but storms firing up in the afternoon should prevent it from
topping out close to the mav guidance of upper 80s.
Short term /Friday night through Sunday/...
as of 310 PM EDT Thursday...
Upper ridge expected to shift east as stronger upper trough moves
from the upper Midwest into the Great Lakes. Models agree that a southern
stream upper shortwave with enhancement in the jet will streak over
the Gulf Coast states and across the western slopes of the Appalachians
Sunday. For Saturday though...mainly looking weak flow aloft with
some convergence across the mountains per south-southeast flow. Models are favoring a
bit of convection with the Lee trough in the east...mainly from the
eastern WV Panhandle southeast toward the Tidewater. Think the airmass
will be unstable and moist enough to trigger a few storms but
overall upper support is lacking so only seeing isolated coverage
over the mountains and north of a Roanoke to Danville line. More sun
Saturday will bring temperatures toward 90 out east with middle 80s west.
Sat night...main axis of convection will run from MS-KY...with
little to no chance of showers east of the Blue Ridge after Friday
evening storms wane. With the upper support tracking closer will
have at least slight chance into the mountains late.
Sunday looks active as the shortwave shifts across Kentucky into northern
WV...with strong convergence and lift. Will see high chance/likely
probability of precipitation. Looks like cloud cover could arrive soon enough to keep
instability lower...but enough upper support/shear in the west where
a few storms could produce gusty winds. Highs Sunday will range from
the upper 70s mountains to upper 80s southeast.
Overall...Labor Day weekend looking very warm/hot/humid. Saturday
not too bad rain wise...but stay cool while drinking plenty of water
if outdoors. Sunday appears poor for outdoor activities.
Long term /Sunday night through Thursday/...
as of 300 PM EDT Thursday...
Much of the long term period will be influenced by a mean upper
ridge that will initially reside along and off the southeast
coast...which gradually retrogresses and expands westward into the
Gulf Coast states by the end of the forecast period.
Southeastern ridge will initially be strong enough to deflect any
northern stream energy away from the Blacksburg forecast area...with
main baroclinic zone remaining from the northern plains east into
and through the Great Lakes into New England.
However...tap of tropical moisture riding around periphery of
southeastern ridge likely to remain over/near the Blacksburg
forecast area through at least Monday or Monday night...maintaining
threat for mainly diurnally driven scattered showers and
thunderstorms...some of which may be accompanied by locally heavy
rain considering relatively high precipitable water values expected
over the area.
Gradual retrogression of upper ridge into northern Gulf Coast region
during the midweek period should be sufficient to allow winds aloft
to veer such that influence of tropical moisture tap gradually
wanes...only to be replaced by more aggressive southward intrusion
of northern stream energy and associated scattered showers/storms in
advance of an accompanying decaying cool front into the middle
appalachian and middle Atlantic region in Tuesday-Wednesday timeframe.
Push of Post-frontal slightly drier air may be strong enough to
reduce threat for precipitation across areas north of Interstate 64
by Thursday...but with at least a chance threat for showers/storms
redeveloping by afternoon across the southwestern mountains closer
to decaying frontal boundary and proximity to higher Theta-E air.
Plenty of cloud cover and dewpoints primarily in the 60s should
ensure that temperatures remain close to seasonal averages...mainly
middle 70s to lower 80s across the higher elevations by day with upper
80s across the Piedmont...with mainly 60s at night. Intrusion of
slightly cooler/drier Post-frontal air from the northeast may allow
temperatures to be a few degrees cooler on Thursday.
Aviation /03z Friday through Tuesday/...
as of 730 PM EDT Thursday...
Clear skies across the taf sites this evening. High confidence of VFR
conditions through much of the evening and overnight. Expect some
patchy fog again Friday morning. MVFR/IFR conditions may exist for
a few hours at blf/lwb/bcb...while the remaining taf locations
should remain VFR through the entire taf period. Patchy fog across
the mountains will quickly burn off after sunrise returning those
locations to VFR for the remainder of the period. Scattered
showers and thunderstorms are possible late afternoon/early
evening as a warm front lifts north...however the convection is
expected to be widely scattered so there is currently no mention
of thunder or precipitation in the tafs. The winds will shift to an
easterly direction early in the day on Friday and eventually
become southerly by late in the taf period...with wind speeds
Widely scattered showers and thunderstorms will affect the region
again on Saturday mainly during the late afternoon and early
evening. Should one of these storms develop near a taf location it
could result in a brief period of sub VFR conditions.
An area of low pressure is forecast to move through the Great
Lakes Saturday night and Sunday...the associated cold front
trailing south and moving across the Ohio/Tennessee valleys. Showers and
thunderstorms will likely be associated with this front...this
activity spreading east into the central Appalachians Sunday and
Monday. Shower coverage Sunday/Monday is expected to be more
widespread as compared to Friday and Saturday.
as of 100 PM EDT Thursday ...
The visibility sensor at kdan...Danville Regional Airport...remains
out of service. A part has been ordered. Repairs will be done this Friday.