Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
308 am EST Wednesday Nov 25 2015
high pressure will over New England is going to stay wedged
southwest into the area through the end of the week. A cold front
enters the middle Atlantic and Ohio Valley Saturday into Sunday
bringing an increased chance of wetter weather.
Near term /through tonight/...
as of 253 am EST Wednesday...
Dry high pressure will be centered over the northeast today into
tonight...wedging southward into our area. Southeast flow will start to increase
across the mountains later today and tonight. The 00z NAM is most
aggressive with low level moisture overnight and in printing out quantitative precipitation forecast.
Think the stratocu deck will become more pronounced across the southern
Blue Ridge after midnight but not enough at this time to produce any light
drizzle or rain.
For today we will see mostly sunny skies...though some high level
clouds Wills track by at times. It should be warmer over the far
western County Warning Area than Tuesday with southeast flow/downslope warming...while the
light east/northeast flow keeps highs closer to tuesdays in the
east...so overall highs in the lower to middle 50s expected over our
region....with some upper 40s across the Blue Ridge higher terrain
into the alleghanys.
Tonight...with increase in dewpoints and southeast flow as well as a few
more clouds...look for lows to be in the 30s...coldest in the
Greenbrier/Alleghany Highland valleys. Places like Bluefield and
Richlands could stay in the lower 40s.
Short term /Thursday through Saturday/...
as of 300 am EST Wednesday...
Good travel day for Thanksgiving this year to see family and friends
or start your Christmas shopping. High temperatures for Thanksgiving
will range from the lower 50s in the mountains to the lower 60s in
the Piedmont. The surface high center moves east into the Atlantic
Ocean on Thanksgiving day. We still are expecting the development of
southeast to south flow on the west side of a Lee side surface ridge
axis. Initially fighting drier air...these trajectories will
gradually tap Atlantic moisture and bring it into our region. The
upslope flow will result in a general trend towards increasing
cloudiness across the mountains especially along the southern Blue
Ridge. Also...some patchy drizzle will also be possible Thursday
evening into Thursday night in areas close to the crest of the Blue
Ridge. The NAM is most supportive of light precipitation Thursday
night...while GFS is less impressed and drier. Low temperatures
Thursday night will generally be in the upper 30s and lower 40s.
Any patchy drizzle will end quickly Friday morning as the low level
flow become more southwest in advance of an approaching cold
front. High temperatures Friday will be above normal with readings
from the middle 50s in the west to the middle 60s in the east. With the
trend of the GFS and European model (ecmwf) slower with the arrival of the
showers...decreased probability of precipitation for Friday evening into Friday night.
Allowed for isolated showers in the northwest late Friday night.
Low temperatures Friday night will drop the lower to middle 40s. A
cold front will enter the region on Saturday...but lose its
momentum as its parent upper support races away through New
England...and another low pressure wave forms along the front
across the Arkansas. The European model (ecmwf) and GFS are coming into better
agreement this morning...with the best chance for showers
Saturday across the north and northwest. High temperatures
Saturday will vary from the upper 40s in the mountains to the
lower 60s in the Piedmont.
Long term /Saturday night through Tuesday/...
as of 300 am EST Wednesday...
Its a second wave that will head northeast along the stalled
front...and its eastern flank offer the area a potentially generous
period of rainfall through at least Sunday. We also will be watching
a closed low move eastward out of The Rockies. This system has the
potential of helping to maintain the train of moisture into the
region as it ventures eastward and flow off the Gulf of Mexico
intensifies into our region. At the same time...temperatures will
continue to trend above normal.
Guidance though is not as uniform with the solutions of this
feature with the GFS rocketing it eastward and the ecwmf not as
progressive through this time next week. The differences point
towards a strong cold front on our western doorstep by this time
next week via the GFS. The ecwmf is about 30 hours slower with
this sharp eastward push and strong cold frontal passage...
keeping the area in very warm conditions for this time of year
along with rain across much of the area Tuesday and then
Wednesday of next week. Our forecast will be more in line with an
average of these two solutions.
Aviation /08z Wednesday through Sunday/...
as of 1240 am EST Wednesday...
High confidence for VFR at all sites through the taf period.
Expecting little more than high/middle clouds as high pressure
surface and aloft continues to bring good flying conditions to the
region. As the high moves off the northeast coast and develops a
wedge east of the Appalachians later on Wednesday...winds will
come around to an easterly direction but any lower clouds will
hold off until late Wednesday night.
Extended aviation discussion...
Thanksgiving day and night...a strengthening Lee side wedge and
southeast flow will allow for an increase in cloud cover and
possibly some light precipitation along or near the crest of the
Blue Ridge. MVFR ceilings become more probable during this time
frame...mainly along and east of roa/bcb line.
On Friday and Saturday...timing of an approaching cold front will
make the difference as to the evolution of flight categories
across the region. Currently...the most likely scenario is a
gradual dissipation of The Wedge as southwest flow ahead of the
front increases. Isolated to scattered showers with MVFR ceilings
and visibilities are possible...especially across western parts of
the area late Friday into Saturday as the front crosses through.
Threat of showers will persist into Sunday keeping potential sub
VFR conditions around.