Scientific Forecaster Discussion
fxus61 krnk 231144
Area forecast discussion
National Weather Service Blacksburg Virginia
644 am EST Thu Nov 23 2017
high pressure will be in control across the mid-Atlantic region
through Friday before the next cold front moves through on
Saturday. This will mainly be a dry frontal passage, but will
bring a return of northwest breezes and cooler temperatures
before high pressure builds in again for the early part of next
Near term /through tonight/...
as of 315 am EST Thursday...
Surface high pressure to dominate over the next 24 hrs with
weak and dry upper trough to drift across the central
Appalachians later today and tonight. Starting off the morning
very chilly with this morning's lows even colder then previously
anticipated and have adjusted grids accordingly. Lower 20s and
even some teens in the protected valleys of the mountains, with
mid to upper 20s common east of the Blue Ridge as Thanksgiving
day dawns. With very light winds and mainly clear skies, with
the exception of some thin cirrus initially over the Piedmont
but moving east by midday, afternoon temperatures should rise
quickly but will remain on the cool side of average for this
time of year. Leaned toward the warmer side of guidance however,
which gives upper 40s to near 50s mountains to lower 50s
Piedmont. If cirrus hangs tough in the east and remains thick
enough it is possible that 50 will be about as high as it can
get in some spots in the east. Overall should be a very nice
Holiday given lots of sun, light winds, and temps only a little
cooler than average as mentioned.
For tonight, while the NAM hints at some mid to high clouds
drifting in from the west tonight on back side of weak upper
trough, most other guidance suggests mostly clear. Since clouds
look pretty thin right now over Ohio Valley and if anything
should trend toward dissipating as trough moves across US, thus
am leaning toward the colder guidance for overnight lows tonight
given nearly calm winds and mainly clear skies. Lows should
still be a few degrees higher than this morning given slightly
higher 850mb temps.
Short term /Friday through Sunday/...
as of 314 am EST Thursday...
Surface high pressure and a weak short wave will exit off the
mid Atlantic coast Friday afternoon. Meanwhile, a cold front
over the Great Lakes will continue to track east. In between
these weather features is southwesterly flow that will help
afternoon temperatures warm into the mid to upper 50s. Mild
conditions will continue Friday night with temperatures in the
mid to upper 30s, higher elevations in the low to mid 40s.
Prefrontal showers are expected to move across the mountains
Saturday morning, then maybe east over the Piedmont in the
afternoon. Most models are not impressed with coverage of
showers moving east of the Blue Ridge as low level winds become
westerly rather quickly by the afternoon. The GFS is the wettest
of all the models, carrying measurable precipitation across the
entire area Saturday, however amounts are only a few hundreths.
We took a model blend for pops Saturday and did not totally
rule out the GFS with backing flow early. The best chance for
measurable rainfall will be along western slopes of southeast WV with
isolated showers for the rest of the area. The front moves east
of the Piedmont in the evening, ending any chances for rain
across most of the area. Some light upslope precipitation along
western slopes are possible during the evening as the upper
level trough pivots over the region. Temperatures Saturday will
run warmer than normal with 50s west and low to mid 60s east.
Cold air will filter in overnight, however, mixing will keep
temperatures in the 30s.
Pressure rises behind the front and a pressure gradient over
the mountains will bring breezy and gusty conditions to the area
Sunday morning. Winds will begin to relax during the afternoon
as high pressure builds over the region. Models are warmer for
Sunday with highs ranging from the 40s across the mountains to
the 50s east into the Piedmont.
Long term /Sunday night through Wednesday/...
as of 300 PM EST Wednesday...
Northern stream amplifies briefly yet again later in the
weekend as a short-wave tracks well to our north through
southeast Canada. This will usher in another cold front through
the area early Sunday, knocking back highs 10 degrees or more
from Saturday, generally low 40s northwest to low 50s southeast. Precipitation
will be hydrologically insignificant with this front with only
a few upslope showers or snow flurries possible. Temps will drop
off into the 20s Sunday night. This will be followed by an
expansive ridge of surface high pressure for the early part of
next week with temps rebounding upward roughly 5 degrees Monday-
Tuesday. The only hint of possible precipitation at this point
appears to be Wednesday as another front approaches, but this
too looks quite moisture-starved. No end in sight for what is
turning into a very dry month of November.
Aviation /12z Thursday through Monday/...
as of 644 am EST Thursday...
High pressure across the eastern part of the country will
dominate through the valid taf period and into the day Friday.
This will bring light westerly winds and fair weather with VFR
conditions all taf sites through Friday. Cirrus associated with
southern stream energy will shift east and out of the southeast
part of the forecast area by midday today. Satellite imagery
early this morning shows very isolated River Valley fog in parts
of southeast WV but is not expected to impact any taf sites
this morning including lwb. Fog development is not anticipated
tonight either. Winds at taf sites today are expected to remain
at or below 4 kts and will be variable, but with a tendency to
be more out of the west or southwest in the mountains and more
out of the south in the Piedmont.
High confidence in ceilings and visibilities through the taf
valid period. Medium to high confidence in wind direction, high
confidence in wind speed through the taf valid period.
The next cold front with a potential for sub-VFR conditions,
mainly in the west, will cross the area on Saturday. There is
very little moisture with this front and while a few light
showers or sprinkles are possible in the mountains on Saturday
there will be more impact from gusty winds just behind the front
later Saturday and into Sunday. Anticipate gusty winds Saturday
into Sunday in the 15 to 25 mph range for most areas, higher
gusts at higher elevations. Some MVFR ceilings are also possible
on the west side of the Appalachians Saturday into Sunday, but
at this point IFR conditions look unlikely. We should have more
confidence in potential MVFR or IFR ceilings behind this front
High pressure returns on Monday with weaker winds, and no