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FXUS61 KRNK 070944

Area Forecast Discussion
National Weather Service Blacksburg VA
444 AM EST Sat Dec 7 2019


A large area of surface high pressure is centered over the Ohio
Valley. This feature will slide across the northern Mid-Atlantic
and into New England today...then off the East Coast Sunday. A
period of wet weather is expected Monday and Tuesday as a cold
front moves east from the central U.S.


As of 430 AM EST Saturday...

1030 MB surface high extended from the Great Lakes into the
Mid-MS valley. This feature will move east today, building
across the northern Appalachians and into New England. This
orientation will result in a northeast wind today...gusty this
morning over the foothills and piedmont as the pressure gradient
forces a low level surge of air southward along and east of the
Blue Ridge. Weak trough/front along the leading edge of the
building high pressure will get suppressed to the south today
with associated cloudiness this morning fading as we progress
through the day. Clouds banked up against the western slopes
will be the most persist and may linger across the Grayson
Highlands and into northwest NC through the entire day. Cold 
air advection will counter daytime heating resulting with only a
5-10 degree rise today...highs mainly in the 40s. 

For tonight, dry high pressure will be in control, winds light.
The high-resolution models maintain some low level cloudiness 
over western NC and into the Grayson Highlands, but layer should
remain relatively shallow and not yielding any precipitation.
That said, some rime icing possible for terrain which intersects
the cloud base but that should be the extent...otherwise, the 
only impact would be to keep temperatures up a few degrees where
the clouds persist. Elsewhere, the surface based inversion 
should be stronger with mostly clear skies resulting in a colder
night...temperatures dipping into the 20s.


As of 315 AM EST Saturday...

After one remaining day of dry weather on Sunday thank to overhead 
high pressure, the remainder of this portion of the forecast is 
expected to be on the wet side.  

A longwave trough is expected to make slow progression eastward 
through central CONUS. A deep and moist southwesterly flow is 
expected to develop across the region in advance of the upper trough 
associated surface cold front. This region of air will be also 
characterized by associated mild temperatures. However, at the onset 
of the expected precipitation on Sunday night, there may be enough 
pockets of sub-freezing air deep enough in height for the 
development of some sleet for a few locations across the forecast 
area. The one area is expected to be the NC Foothills and the Blue 
Ridge area of SW VA south of Floyd, VA, with another area expected 
to be the higher elevations of SE WV. Little if any sleet 
accumulation is expected. As the night progresses, surface 
temperatures are expected to slowly rise from south to north across 
the area.

Monday into Monday night a generous coverage of rain is expected for 
the area, with the greatest concentrations across the northern and 
western sections of the forecast region. Temperatures will continue 
to be on the mild side for this time of the year. 

For Tuesday, the cold front is expected to cross the area mid-day. 
This will allow for temperatures to continue to be on the mild side 
east of the front. Western sections of the area will see quickly 
falling temperatures in the afternoon, with the potential for some 
pockets of a rain/snow mix at the highest elevations.

For Tuesday night, gusty northwest winds will usher in colder air 
across the region. Rain showers are expected to transition to snow 
showers across the mountains, with enough cold air extended far 
enough east for a mix of rain/snow showers across the Foothills and 
western Piedmont regions.

Temperatures during this portion of the forecast will start around 
or slightly below normal on Sunday, but increase to values averaging 
15 to 20 degrees above normal by Tuesday.

Confidence in this portion of the forecast is moderate.


As of 315 PM EST Friday...

Once the front has moved on, the moist environment of the early
week will be supplanted by drier air and a new surface high 
heading our way from the northern plains. The cold air mass 
behind the front will drop our temps to below normal for 
December, so the end of the week will be chilly.

The next opportunity for active weather will be late Friday or 
early Saturday as a low pressure system comes to us from the 
south. Guidance has been wavering from run to run on the track 
and timing, but there is a good consensus that a surface low 
will bring precipitation around next weekend.


As of 1150 PM EST Friday...

A weak front will continue to sink southward through the region
overnight. Remaining light rain in WV is dissipating as there is
very limited upper-level support and downslope west winds east
of the Alleghany front. The WV precipitation is mainly due to
light upslope, which will dissipate overnight as the winds veer
to the northeast. Low-level moisture will linger west of the 
Blue Ridge with MVFR ceilings likely to continue for many of the
TAF sites overnight, with the exception of KLYH and KDAN, which
should see some periods of VFR. KBLF will be up in the clouds 
and expect IFR conditions with some fog and drizzle to become 
established later tonight. A gradual trend back toward VFR will 
begin after daybreak with all sites VFR toward the end of the 
valid period. However, models hang onto the clouds pretty tough
on Saturday, so have advertised more pessimistic TAFs into the
afternoon than previously indicated. Ceilings may remain MVFR
throughout much of the day west of the Blue Ridge, but
especially along and west of the I-77/New River Valley area. No
precipitation is expected Saturday and fog is not expected
either, so any restrictions to visibility would be entirely the
result of a location obscured by clouds due to elevation.

Winds will veer to the northeast overnight and early Saturday at
all sites, but first across the Piedmont. Speeds will gradually
increase from 5kts overnight to 6-10kts during the day Saturday
with low end gusts possible across the Piedmont by afternoon.

/Confidence in Forecast Parameters/
Ceilings - Moderate to High,
Visibility - High,
Winds - Moderate to High.

.Extended Aviation Discussion...

High pressure should dominate the area Saturday with mostly VFR
conditions. Confidence continues to increase in poor flying 
weather for Monday and Tuesday as a complex low pressure system 
develops to provide low ceilings and rain. The cold front from 
this low pressure system should cross overhead by Tuesday night 
to bring gusty northwest winds for Wednesday.





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