Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 072022

Area Forecast Discussion
National Weather Service Blacksburg VA
322 PM EST Wed Dec 7 2016

An arctic front will approach the area tonight and cross the region
Thursday, a much colder airmass overtaking the region for the
remainder of the week.


As of 322 PM EST Wednesday...

Weak high pressure will provide us with pleasant weather into this
evening.  Clouds will increasing tonight ahead of an approaching
arctic cold front. This front is the leading edge of some very cold
air, originating from Canada. It is time to find your winter gear
for cold weather.

The 12z models continued the trend of going drier with the front.
WPC has cut back their qpf for us. But with such a cold air airmass,
what little moisture there is associated with the front will all get
squeezed out over the mountains. Incorporated a blend of the NAM and
GFS for POPS tonight into Thursday. In any case, we are only talking
about some very light precipitation, mainly trace amounts,
associated with the arctic front with light snow showers western
slopes and potential for a few light showers, sprinkles and/or virga
along leading edge of the airmass change for the Piedmont toward
daybreak Thursday. Low temperatures tonight will range from the mid
20s in the northern mountains to the mid 30s in the Piedmont.

Cold front cross our area on Thursday with limited moisture.
Expect cloud cover to erode rather quickly in the post-frontal
airmass except in the favored southeast West Virginia counties where
stratocu will linger. By Thursday afternoon, period of strong cold
air advection arrives as 850 mb temperatures fall to -6 to -12C.

It will become windy Thursday afternoon with strong pressure rises
and northwesterly 850 mb winds around 35 knots. Wind speeds will
remain below wind advisory levels. However, wind gusts as high as 35
to 40 mph are possible across the highest terrain. High temperatures
Thursday will vary from the upper 20s in the northwest mountains to
the lower 50s in the Piedmont, Temperatures will fall behind the 850
mb front Thursday afternoon. Wind chills will vary from the teens in
the northern mountains to around 40 degrees in the Piedmont Thursday


As of 322 PM EST Wednesday...

On Thursday night, gusty northwest flow will continue in the wake of
the departing cold front. Across southeast West Virginia, and
perhaps the first tier of neighboring counties in southwest
Virginia, will experience upslope cloud cover and some isolated to
scattered snow showers or flurries Thursday night into and through
the day on Friday. Coverage will gradually decrease during this time
frame, with ultimately western parts of western Greenbrier County
being the last to see and end to the activity as flurries Friday
evening. Any snowfall will be on the light side with western
Greenbrier County experiencing the most snow with an amount by
Friday evening around one inch. The remainder of the region will
experienced limited or no cloud cover, especially in locations east
of the crest of the Blue Ridge during this same time period.

On Saturday, high pressure will build across the region and allow
for weakening winds and very little cloud cover.

Temperatures will trend colder heading into the weekend. Friday
night the area will experience the coldest night of the next seven
nights. Expect lows to be in the teens across the mountains with
reading around 20 or the lower 20s across the Piedmont.

The combination of gusty winds and lower than average low
temperatures will allow the wind chill readings to reach the single
digits across the mountains and teens across the Piedmont late
Thursday night into early Friday morning. At elevations above 3500
feet MSL, wind chills may dip to around five degrees below zero for
a few hours.

Friday night, despite colder temperatures, wind chills will be
slightly milder thanks to weaker wind speeds.

Saturday night, temperatures will be a bit milder than the previous
two nights thanks to the center of high pressure shifting to our
east. This will will allow for an increasing southwest flow across
the area and an increase in cloud cover associated with our next
approaching system.


As of 322 PM EST Wednesday...

During this portion of the forecast, our region, and much of the
central and eastern parts of the U.S. will be within a pattern of
zonal flow or general troughiness, model dependent.  Each of which
offers a series of shortwave troughs moving through the overall
pattern that will impact our region. Timing of the features differ,
with GFS and Canadian solutions about twelve hours quicker
regarding arrival and departure as compared the ECMWF - Sunday
afternoon through Monday morning versus Sunday night through Monday

Low level thermal profiles differ among the guidance with specifics
very questionable this far in time, especially regarding the notable
differences in timing. Given the area will be within a region of
warm air advection in advance of the system, regardless of timing,
is seems reasonable that some location with the forecast area will
be experiencing some for of wintry mix besides a rain versus snow
forecast. However, given the uncertainties at this time, a rain
versus snow, or a rain/snow mix, are the only two p-types being
offered in the forecast at time time regarding this system.

The forecast for Wednesday is equally, or perhaps a bit more,
uncertain. Where the GFS has a substantial amount of coverage of
precipitation from the Gulf to the Great Lakes in association with
the passage of another shortwave trough, ECMWF has a much weaker
system traversing our region. The GFS wants to tie both a northern
stream wave with a piece of energy ejecting out of the western Gulf.
The ECMWF keeps any wave in the Gulf disconnected, the thus has the
drier solution for our area. Our forecast will reflect a rain versus
snow forecast with more weighting placed on the wetter GFS solution.

Temperatures will trend warmer Sunday into Monday with some cooling
Tuesday, before another slight warm-up in Wednesday. As a whole,
this time period will average a few degrees plus or minus of normal
temperatures for this time of year.


As of 1241 PM EST Wednesday...

VFR conditions will prevail this afternoon into tonight for all
terminals. SCT to BKN MVFR clouds may drift into the western
mountains for a few hours this afternoon. Clouds will increase
tonight ahead of an arctic cold front. In the west, MVFR CIG
may develop after 09Z Thursday at KBCB,KBLF and KLWB. Meanwhile,
VFR Conditions expected in the east outside of MVFR light
precipitation. Arctic front will pass through the Mid-Atlantic Region
Thursday. System is moisture starved, but still may produce a few
rain/snow showers in advance of the boundary Thursday morning, and
virga with potential for a few sprinkles across the VA/NC

Medium to high confidence in ceilings, visibilities and winds
during the taf period.

Extended aviation discussion...

After the frontal passage, cold blustery conditions will develop
for Thursday night into Friday, with upslope snow showers along
the western slopes of the Appalachians. MVFR cigs will be found
across the mountains with VFR east of the Blue Ridge. Tempo MVFR
vsbys will be associated with the -snsh. West to northwest winds
behind the front will be strong into Friday with gusts likely
topping 25-30 kts at times. Winds and any residual low level cloud
cover should quickly fade by Saturday as high pressure builds
overhead making for overall VFR conditions this weekend. Next
weather system to follow will be a cold front, models suggesting a
Sunday Night arrival.




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