Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 211305

Area Forecast Discussion
National Weather Service Blacksburg VA
905 AM EDT Wed Sep 21 2016

An upper low will meander about eastern North Carolina and South
Carolina through late week before finally shifting out into the
Atlantic ocean. High pressure will gradually build in from the
west during the latter half of the week. A backdoor cold front
drops south through the area later Saturday followed by cooler
high pressure Sunday into Monday.


As of 905 AM EDT Wednesday...

Made some minor adjustments in temperatures shaping towards
sfc obs and lamp guidance for this morning, then allowing for a
rise in the east this afternoon. (Clouds cover and scattered
showers will hold temperatures down this morning in Southside.)
Also, modified pops for this morning with latest WSR- 88d trends
and push isolated chances a little further west for this
afternoon. The Hiresw-arw-east, WRF-arw-rnk and HRRR support the
mention of isolated to scattered showers across the southeast
portions of forecast area. Expecting a nice day under sunshine in
the west and northwest portions of forecast area. More changes
later this morning.

As of 315 AM EDT Wednesday...

Looking at lingering low pressure from Julia combined with upper low
over Eastern NC to keep the eastern half of the forecast area in
clouds for most of the day today. Models in general agreement in
showing a sharp gradient to showers, mainly keeping them southeast
of a line from Farmville to Yadkinville. The 00z ECM is a little
more broad in coverage as far west as the Blue Ridge. The 00z NAM
actually seems to have a good handle of ongoing showers east of our
forecast area, but is showing some higher qpf later today across the
northwest piedmont of NC east of Reidsville into Halifax county
Virginia. For the forecast today, am leaning toward a drier scenario
from the foothills west into the mountains with high chance pops in
the extreme southeast cwa to slight chance/20 pops toward
Lynchburg/Martinsville and Yadkinville. High level clouds will
obscure the sunshine at times as far west as the I-81 corridor with
more sunshine in Southeast WV and generally cloudy in the east.
Highs will still be warm with mid 70s to around 80 expected, but
possibly warmer toward Abingdon and Richlands in the lower 80s.
The gradient today will also tighten to allow a breeze of 10 mph
with gusts to 20 mph especially along and east of the Blue Ridge.

Tonight, the upper low remains fixed across the coastal Carolinas.
At the surface the low jogs somewhat southwest. Orientation for best
shower coverage will wrap tighter toward the coast, so will dry
things out overnight with lingering low chance pops in the evening
in the far southeast from South Boston VA to Reidsville, NC.
Otherwise will be clearing in west but remains mostly cloudy in the
piedmont south of Lynchburg, as well as across the NC mountains and
foothills. Lows should stay mild in the east with mid 60s, with
upper 50s to lower 60s west, which is still about 5 to 10 degrees
above normal.


As of 230 AM EDT Wednesday...

During this portion of the forecast, a upper low over South Carolina
will make slow progress to the southeast, all while an upper ridge
builds over the Ohio and Mississippi Valleys. Concurrently, a broad
upper trough will reside over southeast Canada, and southerly flow
on its west side will propel a backdoor cold front into our region
Saturday into Saturday night.

The result of this transition will be even less coverage of isolated
showers across the south and southeastern portion of the region.
Only the Canadian solution at this point has more of a glancing blow
of precipitation for this portion of the forecast area. The forecast
will reflect the last isolated showers departing the far
southeastern sections Thursday evening.

High pressure will provide for limited cloud cover on Friday into
Friday night with no precipitation forecast. The backdoor cold front
at this point is progged to have little if any precipitation
associated with in Saturday into Saturday night, but an increase in
cloud cover is anticipated. Lower dew point air will start moving
into northern sections of the area by late Saturday night.

Temperatures will continue to average about ten degrees above normal
through Saturday night.


As of 130 PM EDT TUESDAY...

Strong upper ridging centered along the Mississippi River to start the
weekend will gradually get pinched back to the southwest as a rather
high amplitude troughing regime develops over the northeast U.S. by
early next week. This will allow increasing northwest flow aloft to
take shape across the region between the departing 500 mb ridging and
eventual upper level low pressure over New England. Cooler high
pressure expected Sunday into Monday. This before yet another
cold front arrives from the northwest on Tuesday with the next
stronger mid level shortwave. However deeper moisture looks quite
limited with both frontal passages given a dry west/northwest flow
aloft so only including slight shower pops later Saturday west and
again Tuesday. Low level flow turning more east/northeast behind
the initial boundary, per the developing wedge could allow for a
slight uptick in shower coverage southern sections Saturday night,
although iffy for much more than clouds/sprinkles at this point
per lower amplitude/drier ensembles.

Subsequent rounds of decent cool advection look to arrive with
each frontal passage into late Tuesday with potential for Sunday
into Monday to remain quite cool if clouds are more widespread.
This timing continues to vary between solutions as each may be too
strong, although thinking highs mostly 70s Sunday-Tuesday, with
50s for lows and possible 40s valleys Monday morning with high
pressure overhead.


As of 735 AM EDT Wednesday...

MVFR ceilings to affect DAN and at times LYH early then become
VFR. A few showers are possible near DAN but coverage is such that
it was not considered to be mentioned in the tafs. The fog never
developed at LWB, and we should be seeing VFR for most of the taf
period. Winds will be breezy along and east of the Blue Ridge with
the gusts reaching 20kts at times between 16-22z.

Tonight the skies will clear from northwest to southeast to a
point, but remain broken at the high cloud level overnight in the
DAN area. Model forecast soundings with easterly flow suggest
potential for low cloud development or advecting in from the east
along with patchy fog. Will keep it optimistic and go no lower
than MVFR at LYH/DAN/BLF/BCB on vsbys with IFR at LWB late

Extended aviation discussion...

Thursday and Friday, outside of late night/early morning fog/low
clouds, expect mainly VFR conditions. The slight chance of showers
will remain just east of KLYH and KDAN through Thursday night.
GFS/ECMWF have been consistent in filling and lifting out the low
to the northeast on Friday.

A back-door cold front will come through the Mid-Atlantic region
on Saturday. High pressure will build in for Sunday. The chance of
precipitation or any sub VFR conditions will increase through the
day Sunday and into Sunday night.




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