Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 222321

Area Forecast Discussion
National Weather Service Blacksburg VA
721 PM EDT Sun Oct 22 2017

A strong cold front will move through the region late Monday
preceded by a period of heavy rain, then cooler temperatures for
mid week. A similar scenario will play out in the extended
forecast with a warming trend Thursday through Saturday,
followed by a cold frontal passage late next weekend associated
with showers, and cooler temperatures to close out October.


As of 715 PM EDT Sunday...

Only minor updates this evening to temperatures and dew
points. The timing of rain to entering NW NC after midnight
then spreading north by sunrise remains the same. Models are
showing a strong low level jet that could warrant a wind
advisory across the Mountain Empire of SW VA and the NW NC
mountains overnight. However, guidance does not bring these
strong winds to the surface as column becomes very saturated.
Elevations above 3500 feet may see wind gusts up to 45 mph
during the morning hours Monday.

As of 300 PM EDT Sunday...

An active period of weather is expected in the near term period, as
water vapor satellite imagery shows an elongated upper trof from the
upper Mississippi Valley southward to the Gulf Coast. Water vapor
imagery is also indicating the first signs of a wave forming along
this trof in northeast Oklahoma which the short range models
strengthen, and lift northeast as a dynamic negatively-titled trof
late on Monday.

Low level moisture is beginning to return to the area with mid to
upper 50 dew points nosing into the piedmont early this afternoon.
Many of the high-res models, including the HREF, bring stratus and
light precipitation, especially in the southern Blue Ridge, after 03Z
tonight on easterly upslope flow.

Trended toward the warmer guidance for lows tonight, especially in
the mountains, but longer period of radiational cooling east of the
Blue Ridge may allow temps to fall near guidance.

Good surge of moisture, with PWATS projected to be 1.5 - 1.7 inches
surges into our area in advance of the approaching upper level
system. These values would make the top 15 for the month of October
at BCB and exceed 200% of normal. With the cold front not passing
until after 00Z...expect 8-12 hours of upslope precipitation
especially in NW NC, where SREF plumes show a wide range of precip
amounts from 1.25 to 5 inches. With dry antecedent conditions and
fairly fast movement to the precipitation expected, will not issue
any flood/flash flood headlines, but minor flooding is expected.

Another concern for Monday is the threat for isolated tornadoes and
locally damaging winds. While instability is minimal, 0-6KM Bulk
shear values are expected to be greater than 50 kts on Monday.
Models are also in good agreement in developing a meso-low to our
south, and lifting it into western Virginia late Monday
afternoon/early evening, enhancing low level helicity values. Will
continue to address the threats for minor flooding and isolate
tornadoes/wind damage in the HWO and briefing slides.

Breaks in the clouds in the eastern portion of the forecast area
(DAN/LYH) may allow temps to exceed guidance, but went near
guidance elsewhere for highs.


As of 330 PM EDT Sunday...

Heavy rain will end by midnight Monday night followed by partial
clearing as the cold front moves east of the forecast area.
Initial post frontal environment will bring some cooling and
drying, but a more substantial drop in thickness will not take
place until late Tuesday and Tuesday night associated with the
upper level trough. This suggests Tuesday will remain relatively
mild, especially east of the Blue Ridge where temperatures may
test 70 degrees with some sunshine. Cold air advection
associated with the upper trough will be more prominent across
the mountains west of the Blue Ridge Tuesday afternoon, and then
areawide for Tuesday night into Wednesday. Model soundings
indicate very little moisture aloft for precip Tuesday except
for maybe the far west.

From Tuesday night into Wednesday and Wednesday night, forecast
attention will be focused around a cold upper level trough which
will be passing overhead with 85h temps of minus 2 to plus 2 deg
C. Any lingering moisture with the trough will be mainly
confined to the mountains west of the Blue ridges with lingering
low level cloudiness and potential for some sprinkles or
flurries depending on the boundary layer temperature at the
time. QPF numbers are minimal, a trace to a few hundredths, so
not expecting anything measurable with respect to snow.


As of 345 PM EDT Sunday...

High pressure will build back across the southeast United States
for the end of the week promoting warming temperatures Thursday
through Saturday with high confidence for fair dry weather
associated with sunny skies both Thursday and Friday.

For the weekend is looks like we are going to repeat the current
scenario with the development of an amplified upper level trough
over the central United States which will move east pushing a
cold front through the area over the weekend.

The GFS is still the faster of the models bringing the front
through Saturday night whereas the ECMWF is 24 hours slower
holding off on any appreciable rainfall until later Sunday.
Attm will maintain threat for showers Saturday through Sunday,
but nothing more or less until models can resolve the timing.


As of 720 PM EDT Sunday...

VFR conditions will prevail through midnight, but flying
conditions will rapidly deteriorate after 05Z (1 AM EDT) with
IFR clouds and vsbys due to showers arriving south of a line
from BLF-ROA after midnight, then advancing north to included
mountain sites (BLF-BCB-ROA-LWB) by sunrise. Showers will expand
in coverage during Monday morning with IFR to MVFR vsbys and
cigs persisting through the day.

Low level wind shear (WS020/16035KT) maybe an issue across the
mountains between midnight and noon.

High confidence in ceilings and visibilities throughout the TAF
valid period.

Extended Aviation Discussion...

A deep upper trough and associated strong cold front will move
into the region from the west Monday night/early Tuesday with
sub- VFR conditions in rain/showers along with increasing wind.
Colder, blustery, unsettled weather with perhaps largely MVFR
conditions across the mountains will linger through the later
half of next week. MVFR showers may return by early next week.




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