Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 081747
Area Forecast Discussion
National Weather Service Blacksburg VA
1247 PM EST Thu Dec 8 2016
A strong push of cold air will overtake the region today and
tonight behind the passage of an arctic front. This cold airmass
will stick around through Saturday before beginning to moderate
ahead of a cold front that will approach late Sunday Night.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1230 PM EST Thursday...
Adjusted cloud cover for this afternoon with increase
along the eastern slopes of the Blue Ridge. Made some minor
changes in temperatures for this afternoon.
As of 857 AM EST Thursday...
Made some minor adjustments in temperatures with sfc obs and
trends for this morning, then leaned early this afternoon
temperatures towards lav guidance. more changes later...
As of 500 AM EST Thursday...
Hope everyone is ready for a little polar plunge.
Weather change is underway. An Arctic front will cross the
forecast area from west to east today, moving through the
mountains this morning, and across the piedmont this afternoon.
Aside from cloud cover, moisture depth associated with the front
is pretty scant, so no more than a sprinkle or flurry at best with
the actual passage of the front. Low level forcing from
increasing northwesterly upslope wind flow, provide a better chc
for mountain flurries tonight and early Friday with some light
accumulation of snow for the WV Highlands where 1 to 3 inches of
snow is possible for northwestern Greenbrier County, northwest of
Lewisburg. Elsewhere only trace amounts expected, with no
accumulation east of the Blue Ridge were downslope flow and
drying will result in clear skies tonight.
Highs today will occur early, then steadily fall after the frontal
passage. Warmest readings will once again be across southside VA and
the piedmont of NC with highs around 50. Mountain counties will
make an early effort to test 40, but then begin pulling back
toward and then below freezing this afternoon. Winds will also
increase behind the front, wind chills becoming a factor,
especially at the higher elevations.
Strong cold air advection and blustery conditions will be in full
swing tonight, 850 mb temperatures falling to -6 to -12C. This
will result in surface temperatures in the lower to mid 20s east
of the Blue Ridge, near 20 for the Shenandoah, New River and
Greenbrier Valleys, and teens for elevations above 2500 feet, and
potential for upper single digits for elevations above 4500 feet.
Add the blustery NW wind, and wind chills will range from the
teens east of the Blue Ridge to the single digits west of the Blue
Ridge, and sub-single digits (zero to 10 below) for elevations
above 3500 feet.
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.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
As of 430 AM EST Thursday...
Modified Arctic airmass will still be in place Friday with cold
temperatures (some 10-15 degrees colder than 1980-2010 climo
normals) and even colder wind chills especially in the western half
of the forecast area. Moderation to temps then begins later Friday
into the weekend with a frontal system beginning to reach our area
Friday: Abundant sunshine for will help raise temps from very cold
lows somewhat, but it won`t feel that way as northwesterly winds 10-
15 mph lead to daytime wind chills in the teens west to the 20s/low
30s out in the Virginia piedmont. Will have some lingering clouds
and snow showers in the hilly terrain in western Greenbrier County,
though with the snow growth region only partially saturated that
will tend to limit any accumulations in that area to an inch or
less. I`ve shown highs ranging from the mid/upper 20s west of the
Blue Ridge into the North Carolina mountains to the mid/upper 30s in
Friday Night: Ridging continues to build into the region allowing
for winds to generally slacken to light west. 850 mb temps still
will be in the -7 to -12C neighborhood. Clear skies, light winds and
dry air mass should allow temperatures to plummet to lows in the
teens to near 20, coldest west of the Blue Ridge.
Saturday/Saturday Night: Start to begin a moderating trend with
surface high pressure becoming centered over our area Saturday and
continuing to shift east Saturday night. Mid-level flow turns zonal
during this period and should be watching a weak 500 mb trough and
associated weak surface low pass to our north over the Ohio Valley.
South-southwest 850 mb winds of around 25-30 kts advect in warmer
air and increasing high clouds, with our 850 mb temps rising to
around -2 to -4C into overnight. Looking at highs in the 30s to low
40s falling back to lows in the 20s Saturday night.
Sunday/Sunday Night: Southwest flow continues to gradually warm the
column in advance of a 500 mb shortwave trough over the Upper
Midwest, that should induce a surface low to develop/strengthen near
the mid-Mississippi Valley and advance to the Ohio Valley Sunday
night. The 00z GFS and ECMWF are at odds as to how strong the 500 mb
trough with the GFS being stronger and a little faster than the
ECMWF. Though timing shortwaves in fast zonal flow is a challenge, I
opted to lower PoPs down into the slight chance range until Sunday
evening. I focused the Chance PoPs more into Sunday night but that
still may be too fast. Temps should be warm enough for rain at onset
except mixing with snow across the higher elevations above 3000`.
Highs Sunday in the upper 30s to low 40s, falling only slightly to
lows at or a few degrees above freezing.
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 400 AM EST Thursday...
Aforementioned frontal system is depicted generally by most of the
global models to lift over or just northeast of the central
Appalachians on Monday. PoPs were raised into the high Chance/low
Likely range. Compared to the 12z guidance, it appears that thermal
structure has warmed enough aloft to support a p-type of rain given
surface temps above freezing, except perhaps at the highest
elevations, but a general transition to rain is anticipated in those
areas as well.
There still remains less clarity regarding to the system moving in
for Wednesday. 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.
As a whole, this time period will average a few degrees plus or
minus of normal temperatures for this time of year.
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 1247 PM EST Thursday...
Arctic cold front will push east across the region this afternoon
into tonight. Gusty northwest winds and mountains snow flurries
and MVFR snow showers will hinder aviation operations tonight
VFR conditions will prevail tonight into Friday East of the Blue
Ridge. Meanwhile, MVFR cigs with mountains flurries and snow
showers will develop west of the Blue Ridge tonight and continue
Wind direction tonight into Friday will be from the northwest.
Speeds generally 6-12 kts with gusts up to 25 kts. An isolated
gust up to 30 to 35 kts may be possible across the highest
Medium to high confidence in ceilings, visibilities and
winds during the taf period.
Extended aviation discussion...
Cold and blustery continues into Friday afternoon, with MVFR cigs
across the mountains with flurries and tempo MVFR vsby for WV.
Widespread VFR anticipated east of the Blue Ridge. 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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