Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201142

Area Forecast Discussion
National Weather Service Blacksburg VA
742 AM EDT Sun Aug 20 2017

High pressure, centered over New England and the mid-Atlantic,
will support relatively dry weather through today. This high
will gradually drift east tonight and Monday, allowing winds to
shift southerly and return deeper moisture into the area.
Another cold front will approach the area by the middle of the
week, bringing with it another chance for showers and storms.


As of 745 AM EDT Sunday...

Main concern this morning is river valley fog across the
mountains, which is locally reducing visibility to a few hundred
feet in spots. Clear skies otherwise and strong heating will
cause this fog to burn off quickly after 9 AM.

Strong heating will support the development of scattered clouds
during late morning/early afternoon, more so across the
mountains. Models continue to hint at a few showers developing
along the Blue Ridge during mid afternoon, possibly a
thunderstorm, however instability appears quite limited due to
warm mid level temperatures, and believe that any rainfall will
be isolated and short-lived. With winds gradually shifting more
southeasterly through the day, afternoon high temperatures are
expected to top out a degree or two above those for yesterday,
ranging from the mid 80s to the low 90s.

Any shower activity is expected to fizzle quickly toward sunset
as daytime heating ends. Winds will continue to shift more
southerly ahead of another approaching cold front, allowing
dewpoint temperatures to gradually notch upward. As such,
believe river valley fog will be a little more widespread on
Sunday night.


As of 300 AM EDT Sunday...

High pressure will push east of the Virginia coast Monday into
Monday night. With some weak southerly upslope flow, solar
heating and marine moisture, scattered showers and thunderstorms
are possible along the Blue Ridge Monday afternoon. Any
afternoon storms will then drift east in zonal flow and fade
over the foothills Monday evening into Monday night.

Cloud cover Monday afternoon should not hinder viewing of the
solar eclipse. The eclipse, coming over the region during peak
heating, may hamper afternoon convection to isolated coverage.
Temperatures during the eclipse may drop 3F to 5F, especially
south of a line from Richlands VA to Mount Airy NC. Temperatures
will rebound following the solar eclipse with daytime highs
ranging from the upper 70s in the mountains to near 90F across

Any convection should end before Midnight, leaving clear to
partly cloudy conditions. Low temperatures Monday night will
range from the lower 60s in the mountains to the lower 70s in
the Piedmont.

On Tuesday, high pressure will move further out into the
Atlantic ocean and lose its hold on the region as a cold front
approaches from the west. Isolated to scattered diurnal
convection may be possible Tuesday afternoon into Tuesday night.
High temperatures Tuesday will be above normal with readings
from around 80 degrees in the west to the lower 90s in the east.
Along and ahead of the cold front, some showers may push into
the mountains Tuesday night. Low temperatures Tuesday night will
generally be from around 60 degrees in the west to the lower
70s in the east.


As of 300 AM EDT Sunday...

A cold front will travel east across the region Wednesday. This
boundary will enter the mountains Wednesday morning and cross
the Piedmont Wednesday afternoon.

This may leave a minimum or shadow of rainfall along the Blue
Ridge and foothills. The best low level jet is north towards DC
and with the winds coming around to the west quickly, the severe
threat will be limited. The exception to the rule will be
across NW NC piedmont and Southside VA late in the afternoon and
into the evening, where instabilities will be high. Best LI
values were around minus 2 to minus 6 in the east.

Following the front Wednesday night, cooler drier air will move
into the region and remain into next weekend. The GFS is
hinting at a shortwave rotating around the upper trough and
generating some convection in the mountains Friday afternoon. As
the high shifts east from the Great Lakes Sunday into Monday,
some moisture may return to the mountains.

Temperatures will likely be cooler than normal by 5F or 10F.
Humidity levels will also be comfortable as dew points drop into
the 50s.


As of 745 AM EDT Sunday...

Main concern this morning is river valley fog across the
mountains, which is locally reducing visibility to IFR/LIFR,
including LWB and BCB. Clear skies otherwise and strong heating
will cause this fog to burn off quickly after after 20/13Z.

Scattered CU will develop during early afternoon, with bases
between 4 to 6 kft. Models hinting at isolated to widely
scattered, short-lived showers developing along the Blue Ridge
during the 20/18Z to 20/23Z timeframe, but not enough coverage
to mention in TAFS. Expect to enter Sunday evening under mostly
clear skies as CU/convection fizzles with the loss of daytime

With winds shifting southerly on Sunday evening, expect
dewpoints to be on a gradual rebound. Another night of mostly
clear skies and light winds are expected to support increased
coverage of river valley fog.

Extended Aviation Discussion...

Moisture will increase Monday and Tuesday as high pressure
weakens and moves offshore ahead of another cold front that
will arrive from the northwest around midweek. However still
appears it should remain mainly VFR Monday into Tuesday with
localized MVFR under isolated to widely scattered convection.
Late night/early morning fog will also be possible each day.
Better potential for sub-VFR will come Wednesday when possibly
more widespread showers and storms arrive with the next cold


As of 400 AM EDT Sunday Aug 20th...

KFCX doppler radar expected to be down for the rest of the
month due to a failing bull gear. Technicians are working on the
radar through this week and the radar will most likely stay
down completely as the repairs are being made.




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