Scientific Forecaster Discussion
fxus61 krnk 190218
Area forecast discussion
National Weather Service Blacksburg Virginia
918 PM EST Mon Nov 18 2019
an upper level disturbance will exit the area tonight while another
one crosses the mid Atlantic on Tuesday. High pressure should
return by Wednesday, but a cold front will arrive later in the
Near term /through Tuesday/...
as of 913 PM EST Monday...
Trend in the latest high-res models and satellite shows low
clouds and fog will maintain its presence through the night. Fog
appears dense at times, especially in the Piedmont per weather
cams and Airport observations. Fog is at times dense in the
mountains, but more patchy. Surface visibility will stay under 3
miles across the Piedmont and areas of dense fog where
visibilities drop to under a half mile will be common especially
toward dawn. Given this, have added a dense fog advisory the
Piedmont of Virginia into Rockingham and Caswell County, NC til 9am.
Patchy nature of fog further west will be handled by a Special
Weather Statement as models showing more mixing out of the lower
visibilities by dawn.
Rain has also moved out, so not changes to the precip forecast
Previous discussion from early this evening...
Not much rain left on radar in the Piedmont of Virginia as main
lifting ahead of shortwave tracks out toward northern Virginia into
the Tidewater. Seeing plenty of lower clouds and fog especially
along/east of the Blue Ridge. There are some models showing
threat of areas of dense fog across the Piedmont overnight, so
may have to issue a dense fog advisory, but having the lower
stratocu in place now is keeping fog at Bay.
The main dense fog this evening has been along The Spine of the
Blue Ridge. As the flow turns west overnight have this fog
abating. Will cover this with an Special Weather Statement for now.
The lingering moisture on the western side of the forecast area
is limited, and not really expecting much if any precip outside
patchy drizzle/perhaps freezing drizzle western Greenbrier, so
took out the snow.
Previous discussion from early this afternoon...
A lingering cool wedge of high pressure and an approaching upper
level disturbance is keeping the mid Atlantic under cloudy
skies with light rain moving across the Virginia/NC border. Pops were
increased a little more to accommodate the latest radar trends.
The rain should exit by early tonight as a negatively-tilted
upper level trough swings overhead. Meanwhile, the flow will
turn to the northwest to bring upslope moisture and a few rain
showers across southeast West Virginia after midnight. Some of
that rain could change to snow in the higher elevations of
western Greenbrier County and maybe near Burkes Garden.
More fog and low clouds are expected overnight into early
Tuesday morning. Another shortwave trough will cross overhead
during Tuesday, which will prolong the chance of upslope showers
across the higher elevations west of the Blue Ridge. Confidence
is low that skies will clear much on Tuesday due to the
shortwave trough, and it would not be a surprise if cloud cover
is still prevalent by midday. Some partial clearing late in the
day may allow Tuesday afternoon high temperatures to reach the
50s in the Piedmont, but the mountains will remain in the 40s.
Short term /Tuesday night through Thursday night/...
as of 115 PM EST Monday...
Winds pick up out of the northwest Tuesday night with about a 30
knot low level jet and modest cold air advection. Warm air advection
for Wednesday night through Thursday will bring 850mb temperatures
back up to near +10 degc ahead of the next front. Will be raising
probability of precipitation for all of the mountains, especially
along the western slopes for Tuesday night into Wednesday morning.
Precipitation will end Wednesday in the morning but clouds will hold
in over the mountains for much of the day. Surface temperatures will
keep rain vs snow threat marginal but may still have minor
accumulations in for highest elevations in southeast West Virginia
and from Grayson County into northwest North Carolina Tuesday night.
Broad upper ridging expected Wednesday and Thursday. Surface high
pressure over the central United States will move east Tuesday
night through Wednesday and will be centered over the mid Atlantic
and Carolinas Thursday morning. The high moves off the southeast
coast Thursday night.
Long term /Friday through Monday/...
as of 115 PM EST Monday...
Next piece of the closed southwest upper low moves east on Friday.
The synoptic scale guidance similar taking this feature into the
Ohio Valley but a spread in solution for the timing remains. The
Canadian/GFS are faster while the European model (ecmwf) brings the trough to the
East Coast Sunday morning. Wpc still trending toward the slower
European model (ecmwf) timing. Next long wave trough is digging in the central and
western United States on Monday.
A cold front crosses the region on Friday. The main axis of
precipitation will be tracking through the mountains closer to
12z/8am which is slower than was advertised by the guidance Sunday.
Will be increasing the probability of precipitation for Friday
The upper short wave coming out of the southwest will develop a
surface low along the cold front. This surface low reaches the area
on Saturday and/or Sunday, with the timing questionable as mentioned
before. High pressure will cover the east behind the system through
Monday. The 850mb front may never drop south through the area this
weekend, leaving the mid Atlantic states in the baroclinic zone and
Clouds and rain will keep maximum temperatures on the cool side
Friday and Saturday as well as limit The Drop in temperatures
overnight. Push of colder air will enter the mid Atlantic region
behind the weekend low. Will be cold enough for snow in the
mountains through Sunday night. Drier air and less upslope will
result in a dry forecast Sunday night and Monday.
Aviation /02z Tuesday through Saturday/...
as of 625 PM EST Monday...
Not looking like a favorable nigh for flying with terminals
stuck in low clouds and development of fog, which could be dense
to LIFR/vlifr at lyh/Dan overnight, and possibly west toward blf
with west flow upslope, while lwb/bcb/roa sink to at least IFR.
The trick will be low IFR clouds vs fog as the low clouds are in
place now, but several models are showing lowering visibilities
overnight, along/east of the Blue Ridge.
Confidence is high on poor flying conditions. Seems models are
starting to lift ceilings/vsbys too fast Tuesday morning so
delayed another 1-3 hours from models having roa/lyh and Dan to
VFR by 15z-16z, and the mountains in the 18-21z time frame.
Extended aviation discussion...
May see some gusty winds Tuesday night from the northwest.
Otherwise VFR mainly east with possible MVFR in the mountains
Tue night-Wed, with westerly flow and possible snow showers.
High pressure builds in late Wednesday into Thursday with VFR.
A front and upper disturbance will bring threat of rain and
sub-VFR for Friday into the weekend.
Virginia...dense fog advisory until 9 am EST Tuesday for vaz033>035-
NC...dense fog advisory until 9 am EST Tuesday for ncz005-006.