Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 230353

Area Forecast Discussion
National Weather Service Blacksburg VA
1053 PM EST Wed Feb 22 2017

Weak high pressure off the mid-Atlantic coast will stay
situated here through Thursday morning. A frontal boundary
across the Great Lakes into the southern Plains shifts slowly
southeast to the Ohio Valley by Friday. The main cold front
across the midwest will pass through our area Saturday.


As of 1030 PM EST Wednesday...

Dense Fog Advisory until 10AM Thursday.

Rain has ended, but still leaves the forecast area in a moist
stance with the relative humidity near 100%. Combine this with
clearing skies aloft and conditions are ripe for dense fog per
radiational cooling paving the way for a super saturated
boundary layer. Lowest elevations appear to be most suseptive to
fog formation with near calm winds. Light winds at ridge top
level will provide a bit more mix and less of a problem for
elevations above 3000 feet.

For the remainder of the overnight the main forecast focus will
be on the fog. Forecast soundings maintain shallow layer of
moisture near surface with clearing aloft. With weak wind flow,
the stable air will keep this moisture trapped near the surface
until daytime mixing can scour it out Thursday.

Thursday, frontal boundary situated from the Eastern Great
Lakes, southwest to the Southern Plains, in the morning, will
slowly advance south to a PIT-IND-TOP line by late in the day.
Models break the in-situ wedge as sfc flow turns more southwest.
Will see more sunshine in the piedmont in the afternoon, with
sunshine at times in the west followed by more clouds ahead of a
shortwave that passes across KY into Ohio in the afternoon.
This shortwave combined with some low level convergence across
the mountains may lead to some showers and even thunderstorms in
the afternoon, mainly from the Alleghanys southwest to southern
WV, with limited coverage southeast to the foothills. As wedge
erodes, expect temperatures to soar to the lower to mid 70s east
of the mountains, with mid to upper 60s across the west. Some
record high temps may be approached and/or broken. See climate
section below. Even record warm low temperatures will be
possible for Thursday 2/23.


As of 250 PM EST Wednesday...

Thursday night through Friday night, the area will be under a region
of deep south to southwest flow, with its origins from the eastern
Gulf of Mexico. A warm front will lift north of the area Thursday
night. While some patchy light rain will be possible early in the
evening for the area of the region west of the Blue Ridge, coverage
will decrease through the night as the front continues heading north
of the area. Lingering upslope light rain will remain possible near
the crest of the Blue Ridge, especially in areas southwest of Floyd,
VA into the Northern Mountains of North Carolina.

On Friday, most of the area will be precipitation-free, save a few
locations near the crest of the Blue Ridge thanks to local upslope

Friday night into early Saturday, a cold front will approach the
region from the west, and cross the area during the day Saturday.
Look for increasing chance of rain showers with the approach and
passage of this feature. There will also be a slight chance of
thunderstorms with the passage.

By Saturday night, the front will be to our east, and northwest
winds will be on the increase. The northwest winds will yield some
gusts approaching 40 to 45 mph at the highest elevations. Also,
colder air will start working its way into the area. Lingering
upslope rain showers across parts of southeast West Virginia, south
into the Northern Mountains of North Carolina are expected to
transition to snow showers by Sunday morning.

Temperatures Thursday night through Saturday are expected to average
about twenty degrees above normal. Saturday night, behind the cold
front, temperatures will fall to readings near normal.


As of 300 PM EST Wednesday...

Gusty winds will continue into early Sunday behind Saturday`s cold
frontal passage. These winds will weaken quickly during the day and
back southwest as the next upper level trough deepens across the
Central Plains.

This same upper trough will move east and be over the Ohio Valley by
mid-day Monday. A warm front in advance of this system will head
north through our region, bringing a return of patchy light
precipitation to the area during the day Monday. There may be an
issue of a brief period of a wintry mix across the northwest section
of the area early Monday as a potential warm nose develops over a
sub-freezing boundary layer and surface. For now, will keep things
simple by reflecting a rain versus snow forecast based solely on
whether the forecast surface temperatures is above or below

Monday night the system`s associated cold front is expected to cross
the area. Look for the precipitation to become more showery Monday
night into early Tuesday.

Model guidance for the remainder of Tuesday into Tuesday evening is
not clear. The GFS is progressive with the cold front making
significant headway east of the region. The ECMWF is not
progressive, stalling the feature over the area, all while
suggesting another wave will move northeast along this boundary,
keeping a generous coverage of rain across the area Tuesday
afternoon into Tuesday night. Our forecast will reflect a blend of
these solutions. While rain will be forecast Tuesday afternoon and
evening, it will not be to the degree offered by the ECMWF.

For late Tuesday night into Wednesday, model agreement improves with
solutions bringing yet another upper low/trough from the Central
Plains states into the Ohio Valley. Warm frontal rain is expected
late Tuesday night into early Wednesday, with a generous coverage of
showers and some isolated thunderstorms across the area Wednesday
afternoon coincident to the cold frontal passage.

Temperatures Sunday and Monday will be normal for this time of year.
Reading moderate through mid-week with temperatures some ten to
fifteen degrees above normal expected.


As of 1030 PM EST Wednesday...

Dense fog advisory along and just east of the Blue Ridge through
10am Thursday. In spite of clearing aloft, a very moist
boundary layer with RH values of 100% has allowed for the
formation of dense fog with widespread visibilities under 1/2SM
Lack of wind will allow this fog to persist through mid-morning
Thursday before daytime heating begins to mix the boundary layer
and allow for improvement. Until then expect Widespread LIFR.
This is a situation where the valleys and lowland areas will
contain more stratus and fog as compared to the ridges. Ridge
tops will likely remain above the stratus layer.

The fog/stratus looks to burn off Thursday morning with a
return to VFR conditions by the afternoon. However, a weak
frontal boundary will brush the region as an area of low
pressure moves through the Great Lakes region tomorrow. This may
bring a shower to locations west of the Blue Ridge so will
include VCSH after 18Z all sites except KDAN and KLYH. Winds
will be light through the period.

Extended Aviation Discussion...

Thursday night-Friday, we will be well into the warm sector
with VFR conditions and much above normal temperatures. Surface
wind gusts of 20 to 30 kts possible across the higher terrain.

Band of showers and isolated thunderstorms with MVFR conditions arrive
late Friday night into early Saturday along and ahead of a
strong cold front. Drier weather and increasing northwest winds
follow behind the front on Saturday afternoon through Sunday.

Approach of another front Monday will provide increasing clouds
and possibly showers and MVFR cigs to BLF/LWB late in the day.


As of 245 PM EST Wednesday...

Warm temperatures set to occur again Thursday with increase in
westerly flow in the low levels. Question will be cloud cover. At
the moment with some sunshine look for highs and lows to approach or
break records for Feb 23rd.

Thursday 02/23/2017
Site        Record High/Year  Record Warm Low/Year
Bluefield       74 1975          51 1975
Danville        73 1980          50 1981
Lynchburg       74 1943          52 1925
Roanoke         76 1943          54 1925
Blacksburg      69 1980          46 1990


VA...Dense Fog Advisory until 10 AM EST Thursday for VAZ007-009>020-
NC...Dense Fog Advisory until 10 AM EST Thursday for NCZ001>006-
WV...Dense Fog Advisory until 10 AM EST Thursday for WVZ042>044-507.


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