Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 161441

Area Forecast Discussion
National Weather Service Blacksburg VA
941 AM EST Thu Nov 16 2017

A weak cold front will push east of the region this afternoon
allowing high pressure to gradually build in from the northwest
this afternoon through Friday. Another stronger cold front
will then bring more showers and windy conditions to the region
this weekend. Cold high pressure will build in behind the front
for early next week.


As of 940 AM EST Thursday...

850 mb front now crossing the Blue Ridge responsible for a quick
uptick in winds early this morning with better cool advection
now pushing off the Blue Ridge. Latest short term guidance
showing a lingering 35-40 kt northwest jet through the afternoon
as the 5h trough to the north pivots across so likely to be
close to advisory levels at times along the highest ridges.
However morning raobs show a rather high level inversion that
should keep the better speeds aloft despite an added boost in
pressure rises later on. Otherwise expecting mainly sunny skies
east of the Blue Ridge, and over most of the mountains
excluding the far northwest where added upslope clouds likely to
filter southeast before mixing out. Also given such a warm
start and strong downslope offset of any weak cool advection out
east, raised highs a category in spots with mostly 50s west to
mid 60s east.

Previous discussion as of 605 AM EST Thursday...

Brought up winds and wind gusts per latest observations around
the area and mesoanalysis showing best 8h winds arriving around
10am. Still not windy enough for advisory although some of the
highest ridges of the Alleghanys in Bath County could reach
45-50 mph. Also lowered pops and increased clouds a little
further east early on.

Previous discussion from early morning...

Radar mainly quiet this morning with just a few lingering showers in
Halifax County Virginia, and some very light echoes over the New
River Valley. However, surface obs showing some light rain,
sprinkles over WV, far SW VA as upslope kicks in behind front. High-
res models are showing showers thru mid morning in the far western
slopes  though not expecting more than scattered coverage. We get
clipped by 8h thermal trough of zero to -3C in WV to the Alleghanys
today so some flurries/snow showers will be around but no
accumulation. Another wave this evening passing north may send a few
flurries or rain showers toward Greenbrier/Bath for a couple hours
but overall airmass seems too dry to have any precip.

Winds will be gusty through the morning, but best surge of winds
appears to occur toward dusk as 6 hr pressure rises increase to 6
mb, though 8h jet is about 30-40kts. Have increased gusts late
afternoon to early evening but should stay below advisory levels in
the higher ridges.

Model soundings and pattern suggest clouds sticking around  through
the day in Greenbrier to Bath county with cu field spreading
eastward but more scattered into the Blue Ridge north of Roanoke.
Rest of the area should be mainly sunny. Highs today should be
milder than Wednesday despite post-frontal. Winds will keep it
feeling cooler in the mountains but aid in downslope warming lee of
the Blue Ridge. Looking at upper 40s to lower 50s mountains, but
colder in the higher terrain of the Alleghanys, with 60 to 65 in the
foothills/piedmont and Roanoke.

Tonight, winds stay up as mentioned above, but should start to see
it ease off after midnight in the valleys/piedmont as the surface
high shifts into the Central Appalachians by dawn Friday.

Should see lows in the mid to upper 20s in the valleys and parts of
the piedmont with upper 20s to lower 30s elsewhere= where winds stay
up longer. Also upslope appears to keep some clouds around a little
longer over the WV mountains toward the New River Valley north and
west of I-81, so this may stall temps a little.


As of 200 AM EST Thursday...

During the Friday into Friday night time period, an upper level
ridge is expected to build over the area, all while a broad region
of surface high pressure extends north to south across the U.S. east
coast. By Saturday, both of these features will be shunted to the
east in response to an approach upper level shortwave trough across
the western Great Lakes region and an associated approaching surface
cold front. The resultant weather pattern for our area during this
time period will be for moderating temperatures, increasing cloud
cover, and precipitation along our western extent by late in the day

Saturday night the cold front is expected to race eastward across
the region. The front itself is forecast to present a narrow strip
of moisture coincident to the passage. This feature is expected to
bring measurable, albeit, light precipitation to the entire forecast
area. A more prolonged period of light precipitation is expected
across parts of southeast West Virginia, south into the Northern
Mountains of North Carolina Sunday, then becoming less organized and
sparse heading into and through Sunday night.

Increasing, strong, northwest flow behind the front will be
responsible for this prolonged period of additional light
precipitation. Model guidance is suggesting northwest 850mb winds
will peak in the 40 to 50 kt range on the backside of the departing
front, with decent pressure rises and cold air advection. Confidence
is still high enough for an wind outlook in the Hazardous Weather
Outlook during the Saturday night and early Sunday time period.

As the cold air enters the region, look for scattered snow showers
to become more probable, especially across portions of southeast
West Virginia, south into the higher elevations of neighboring
southwest Virginia, and farther south into the Northern Mountains of
North Carolina.

Temperatures on Sunday will be tricky. While a true diurnal
curve is not expected, neither is an all day temperature
decrease thanks to the the northwest flow cold air advection. A
mix of the two seems most likely, with better chance of some
warming in the east thanks to strong subsidence, and a better
chance of limited temperature movement in the west thanks to a
greater abundance of cloud cover.

On Sunday night, drier and colder air will continue to enter the
region on strong northwest winds, although they will be trending a
little weaker. Look for any lingering isolated snow showers in the
far west to decrease in coverage and finally end during the night.


As of 130 PM EST Wednesday...

Winds should slowly diminish Monday as the upper trough lifts out
and high pressure builds in from the southwest into Tuesday. Another
weak mid level feature likely to pass across Tuesday night into
Wednesday before the high weakens and the split flow begins to tap
return flow moisture resulting in more clouds Day7 but dry at this
point. However will stay below seasonal normals with only a slight
boost in highs on Tuesday at this point.


As of 620 AM EST Thursday...

Upslope clouds will keep MVFR cigs at BLF til 14z, before drier
air mixes out the lower clouds, though VFR cigs off and on in
BLF/LWB can be expected through the day, while it stays
scattered to clear to the east of the mountains.

Northwest to west winds will be gusty with most taf sites
gusting to 20kts through mid afternoon, before waning this
evening, though another surge of winds may bring another 2-4 hr
period of gusts around 20kts to LWB/ROA/BCB around 00z.

High pressure will build in late keeping all sites VFR.

Extended Discussion...

VFR conditions anticipated through Friday. A cold front is
expected to cross through the Mid Atlantic region Saturday
with precipitation and strong winds both ahead of and behind the
front. Gusty winds may continue into Sunday but there is large
spread in the guidance at that time frame. Dry weather expected
Monday into Tuesday.




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