Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 240202

Area Forecast Discussion
National Weather Service Blacksburg VA
1002 PM EDT Thu Mar 23 2017

High pressure will slide off the coast tonight into Friday. A
warmer southerly flow will develop Friday into the weekend ahead
of a slow moving cold front that will approach the region
Sunday. A series of upper-level low pressure areas will track
across the central and southern U.S. through next week keeping
an unsettled weather pattern in place.


As of 1002 PM EDT Thursday...

Update to lower forecast low temps across the western valleys and
out east given lingering very dry air per evening soundings and
latest obs. This in conjunction with possible development of a weak
bubble of high pressure over the east given ridging aloft, likely to
allow good radiational cooling again tonight despite 850 mb warming
as well as slowly rising dewpoints. Also band of broken mid/high
clouds just west of the mountains likely to fade initially upon
encountering the very dry air aloft so appears will stay clear
longer espcly eastern half. Again expect some 20s in the western
valleys and perhaps outlying areas across the east with overall
low/mid 30s elsewhere, except around 40 across the higher
ridges where better warm advection mixing will occur.

Previous update as of 705 PM EDT Thursday...

Forecast looks to be in pretty good shape through the next few
hours, as clear skies for the first part of the evening allowing
for temperatures to plummet quickly after sunset. I did make
some changes for the late evening into the overnight period.
Leading edge of warm front and a broken to at times overcast
mid-level cloud shield extends roughly NNW- SSE from northern
Illinois southeastward to the eastern Tennessee Valley. This
cloud shield should advance eastward into our western counties
around midnight and continue lifting in a northeastward fashion
across the New River/Roanoke Valleys into the southern
Shenandoah counties overnight, as reflected in past couple RAP
model 700-300 mb RH profiles. Though Virginia Southside towns
into the NC foothills and Piedmont probably stand to radiate
fully the whole night...given that the clouds may be thick
enough to impede or stop radiational cooling entirely elsewhere,
I`ve utilized some of the warmer temperature guidance after
midnight to reflect a slower cooling in cloudy areas. Dewpoints
were also raised upward some overnight, accompanying the
increase in clouds. In the Grayson Highlands and the NC High
Country dewpoints are already on the rise from low afternoon
values are now into the low to mid 20s. Given the trend in cloud
cover, lows in the western counties probably reach lows in the
mid 30s earlier with overnight lows occurring closer to sunrise
in the Piedmont and Southside areas.

Previous near-term discussion issued at 214 PM follows...

Dome of high pressure along the east coast is going move offshore
tonight  into Friday allowing for the area to move into warm
advection. Expect temperatures to drop again tonight to the upper
20s to lower 30s in the east and mountain valleys, except mid to
upper 30s across the higher terrain in the west with southerly winds
picking up more.

Late tonight through Friday, models are showing increasing moisture
in the mid and upper levels tracking from KY/TN into the mid-
Atlantic with some light precip being generated north of our
forecast area. Anticipate some increase in clouds late tonight into
Friday  mainly over the west and north, but still looking at more
sun than clouds Friday as temperature warm into the 60s, except some
50s along the Blue Ridge.


As of 345 PM EDT Thursday...

A pattern transition will be underway this weekend as
predominate northwest flow aloft comes to an end, replaced by
unsettled split flow with series of southern stream storm
systems of Pacific origin to parade across the CONUS. First in
this series of storm systems will arrive Sunday. Until its
arrival, the first half of the weekend will be dry, Saturday
certainly a great day to be outdoors with temperatures in the

Late Saturday, moisture will be on the increase west of the
Appalachians per the approach of an upper low to lifting out of
the Southern Plains. Showers/thunderstorms associated with this
system will be advancing east across the Tennessee Valley into
far southwest VA or southern WV Saturday night. The upper low
will then take a more northward track into the Ohio Valley and
weaken as it encounters the upper ridge along the eastern
seaboard. This will result in a weakening of the thunderstorm
activity as it crosses the mountains, but still sufficient
forcing, instability, to promote high probability of showers
areawide for Sunday. Temperatures Sunday will be just a tad
lower thanks to cloud cover and precipitation, but with
increasing dewpoints, overnight lows will be warmer.

With regard to QPF, models are in fairly good agreement,
advertising 1/2 to 3/4 inch of rain along and west of the Blue
Ridge Sunday, and 1/4 to 1/2 inch east of the Blue Ridge.
Severe weather is not expected for our CWA for this first


As of 400 PM EDT Thursday...

Next in a series of upper-level low pressure areas will move
from the Southern Plains into the Tennessee Valley/Central
Appalachians late Monday into Tuesday. While this system will
again be weakening as it moves toward the western Atlantic upper
ridge, it will have somewhat better dynamics and instability to
work with than the Sunday system. Therefore, a chance of
thunderstorms anticipated areawide for Tuesday afternoon. This
still does not look like a widespread severe weather maker for
our CWA, but slightly better potential for at least some
stronger storms with small hail per warmer temperatures, higher
surface dewpoints and slightly better instability compared to
the Sunday system. Rainfall amounts again appear to be in the
1/4 to 3/4 inch range over all with this event.

A quieter midweek period appears in order as another upper-
level system deepens but slows as it moves into Texas and an
upper ridge amplifies across the eastern U.S. A weak area of
high pressure from the Great Lakes filters into the area for
midweek. By Friday, this aforementioned system will move into
the Mid-Atlantic region as yet another upper-level low pressure
area moves from the southwest U.S. into Texas.

Temperatures will remain mild through the upcoming week with no
significant intrusions of Canadian air. A slight cooling will
be noted midweek, but temperatures will favor the warm side of
normal with highs in the 60s/70s and lows mainly in the 40s to
lower 50s.


As of 709 PM EDT Thursday...

VFR through the period. Initial SKC conditions give way to a BKN
mid-level altostratus deck after 06z and then lifts into
northern Virginia by mid-morning. Should see VFR FEW-SCT cumulus
in the warm sector the rest of the day. Winds light southeast
tonight, then veer and increase to south 5-10 kts, strongest at
Lynchburg and Danville.

Extended Aviation Discussion...

Good flying weather is expected to linger into Friday night before
moisture starts to increase over the weekend ahead of an upper-
level low pressure area moving northeast from the Southern
Plains. Precipitation is not expected until Sunday when sub-
VFR conditions become more of a possibility. Otherwise looking
at overall VFR to start the weekend with most lower cigs
remaining west of the area until later Sunday at this point.
Periods of unsettled weather will continue into the first half
of next week as a series of upper-level lows track from west to
east across the U.S.




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