Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 190514

Area Forecast Discussion
National Weather Service Blacksburg VA
1214 AM EST Thu Jan 19 2017

Weak high pressure builds over tonight, then another storm system
moves over the southern Appalachians by Friday. Another storm system
approaches from the southwest early next week.

As of 1130 PM EST Wednesday...

First of several negatively titled upper systems to move into
the eastern U.S. spreading high clouds across the area this
evening. Needed to increase cloud cover quite a bit overnight to
accommodate the current and expected high clouds that will
overspread the area tonight into Thursday. T/Td readings
generally on track, so only minor changes needed with respect to

AS OF 630 PM EST Wednesday...

High pressure is edging into the region. Clouds along western
slopes will erode through the night. Also on the decline are the
winds as the pressure gradient weakens across the mountains.

As high pressure tracks over the area, good radiational cooling
will send temperatures down into the 30s overnight. There could
be colder temperatures across the mountain valleys, however
saturated ground may limit areas dropping into the upper 20s.

AS OF 315 PM EST Wednesday...

High pressure over western Kentucky this afternoon will build east
overhead tonight. Aloft shortwave along the virginia coast will push
further out into the Atlantic ocean. This will allow the upper
ridge to build east tonight. Low temperatures tonight will range
from around 30 degrees in northwest Greenbrier county to near
40 degrees along the southern Blue Ridge mountains. High
pressure over our region Thursday will slide east into Thursday
night. The upper level ridge swings trough the region bringing
drier weather. Moisture and clouds will slowly increase
Thursday afternoon from the southwest. High temperatures
Thursday will average 8 to 18 degrees above normal with readings
from around 50 degrees in the northwest mountains to around 60
degrees in the piedmont.


As of 315 PM EST Wednesday...

We will be under the influence of a progressive and transitory pattern
an upper ridge moves to our east and a closed low over the midwest
opens up to a progressive open wave, high pressure at the surface will
shift to the coast and leave a lingering wedge in place. The upper trof
will then drive a weakening surface low into the Great Lakes and push a
front with good isentropic lift in to the region from the west. This
will spread precipitation across the Appalachians and central mid
Atlantic region Thursday night into Friday.

By Friday afternoon, the upper trof will give way to some ridging and
ending the bulk of precipitation through some lingering sprinkles are
possible. By Saturday the ridging will give way to a developing trof to
our west and increasing dynamic forcing in a moist environment will
bring an increasing chance of precipitation to our region through
Saturday night.

With no change in airmass, expect temperatures to remain above normal
through the period.


As of 315 PM EST Wednesday...

Guidance remains generally consistent with the big picture details
Sunday into the first part of next week with some variation in the
finer details. A large vertically stacked closed low will move across
the deep south and bring a strong and very moist flow of air to the
region. Several spokes of energy rotating around the low will bring
several surges of precipitation to the region from Sunday through
Monday before the system starts to pull away from the area by Monday
night. So while the main baroclinic zone is now expected to be much
closer to the coast, the overall scenario still favors widespread
precipitation with significant orographic enhancement along the Blue
Ridge. Will continue to keep a close eye on how this situation evolves
as the indicated QPF amounts generally in the 1 to 3 inch range by
Monday night may result in some flooding. Instability to drive thunder
will likely reside closer to the baroclinic zone, though with enough
forcing under the cold core upper low some thunder is possible but
confidence not high enough at this point to include in the forecast.
Will keep ptype as all liquid though dynamic cooling under the deep
upper low may generate thickness values favorable for some wintry mix,
but confidence in this is low. Some wrap around precipitation will
liner west of the Blue Ridge through Tuesday before we can get a brief
break ahead of the next system approaching later Wednesday night.

Temperatures will trend down through Tuesday as the cold core low moves
over the region, though readings will still remain above normal through
the first part of next week.


As of 1200 AM EST Thursday...

The first of several negatively tilted upper systems will
approach the forecast area from the south Thursday night. High
clouds will overspread the area in advance of this system, and
are already doing so. Low clouds linger across eastern WV, but
the lack of a significant west wind field has resulted in
scattering out of the low clouds at KBLF, while they hold in at
KLWB. All indications are that these clouds will gradually
dissipate from the south through the night leaving both sites
KBLF. Otherwise, expect BKN-OVC high clouds throughout much of
the TAF valid period at all sites. Any further sub-VFR ceilings
and precipitation will be beyond the end of the TAF valid
period. No issues expected with visibility through the TAF valid
period. Winds diminishing and becoming light and variable
throughout the CWA. The winds will veer to the southeast through
the day Thursday, but speeds are expected to remain mostly 5kts
or less through the TAF valid period.

Medium to high confidence in ceilings throughout the TAF valid
High confidence in visibilities throughout the TAF valid
period. Medium confidence in wind direction, high confidence in
wind speed throughout the TAF valid period.

Extended Aviation Discussion...

Conditions will begin to deteriorate Thursday night from
southwest to the northeast as a wave of low pressure track
across the Tennessee Valley. Expect periods of rain Thursday
night through Friday afternoon, then again Sunday into Monday.
During this time expect sub-VFR cigs and at times vsbys.




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