Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
325 PM EDT Monday Sep 22 2014
high pressure system will move east tonight covering much of the
eastern United States through Wednesday. Low pressure will develop
along the southeast coast Thursday and Friday.
Near term /through Tuesday/...
as of 230 PM EDT Monday...
High pressure to move over the middle Atlantic late tonight. Clouds
this afternoon will erode in the mountains tonight but at the same
time as upper level system moves across the western Carolinas and
closes off...expect the upper levels to moisten up and send some
cirrus north across the eastern half of the forecast area...though
not too confident on density of the cirrus...but think the sky will
be partly cloudy. Big issue tonight will be temperatures...as winds
decouple...and sky in the west to be clear. Think temperatures will be
dropping into the middle to upper 30s across the valleys of Bath and
Greenbrier with most staying above 37f. Patchy frost in the valleys
appears possible so highlight Bath and Greenbrier in the severe weather potential statement for
patchy frost. Not enough coverage to warrant a frost advisory but
evening shift can take another look at trends in
temperature/dewpoint/wind/sky in case threat of more frost increases.
Nonetheless the coolest night we have had since late may...with
upper 30s/lower 40s mountains...to middle 40s-50 east.
During the day Tuesday...upper low/trough stays over the central
portions of the Carolinas...and mainly keeping a stream of high
clouds situated over the Piedmont. High will be mild with upper 60s
to lower 70s across much of the County Warning Area.
Short term /Tuesday night through Thursday/...
as of 240 PM EDT Monday...
Still looking dry Tuesday night but model differences show up in
terms of this upper trough into Wednesday...and how much moisture
spreads west from the east flow around The Wedge. The European model (ecmwf) has been
persistent in showing this and the 12z NAM is coming into this
trend as well...with the GFS still drier. Think the dry low levels
will take a while to moisten up but late Wednesday night-Thursday should see
enough between the high over the NE/middle Atlantic and a coastal
trough/front/low to bring a slight chance to low chance of rain to
the eastern half of the County Warning Area...with clouds increasing. The Wedge in
place will make for a cooler day Thursday...than Wednesday. Highs
Wednesday with more sun will warm into the upper 60s to middle
70s...then with clouds and light rain Thursday expect middle to
upper 60s where its cloudy with rain chances...with lower to middle
70s across the far SW Virginia corridor heading west of Marion and
Lows will also modify during this period...but still cool Wednesday
morning with lower 40s mountain valleys...to middle to upper 40s most
locations...except lower 50s southeast.
Lows Thursday morning will be in the 50 to 55 degree range.
Long term /Thursday night through Monday/...
as of 300 PM EDT Monday...
Considerable uncertainty exists in the extended period as a
fairly complex upper level pattern develops by the weekend with
highly amplified upper ridge over the north central U.S. Extending
into Canada with troughing over the western Atlantic and across
the western states. The 12z Euro is much further west with
Atlantic trough with resultant surface low meandering along the
middle- Atlantic coast Friday-Sat but not far enough west for precipitation
this far inland. But would likely see substantial cloudiness from
this along with the cad-like effects from a very slow-moving
surface high over the northeast. In fact the upper ridge to the
north retards northward movement of this coastal system well into
Sunday. GFS is much less developed with any coastal system with
dry high pressure in control through weekend. Elected to reflect
more optimistic GFS solution at this point with more sun. Temperatures
near to above normal with mainly 70s and 50s for highs/lows. Both
GFS/Euro show surface low or inverted trough developing over the
lower Mississippi Valley by early next week with grids showing
clouds spreading in from SW to NE as early as Sunday night.&&
Aviation /20z Monday through Saturday/...
as of 100 PM EDT Monday...
West to northwest winds are calming down this afternoon and should be
sustained between 5-10kts into the early evening. MVFR ceilings are
holding on at blf...however it will be scattering out by 21z. VFR
conditions should hold through much of the overnight. Seasonably
cool temperatures are expected to result in some patchy river fog
Tuesday morning as the cool air passes over the much warmer
waters. This should result in a few hours of IFR conditions at lwb
and MVFR/IFR conditions possible in bcb for an hour or two right
around dawn. By 14z Tuesday all taf locations will be VFR and will
stay at those conditions through the remainder of the taf period.
High pressure building in to the north will result in winds slowly
shifting from a west/northwest direction today to an easterly direction on
Extended aviation discussion...
High pressure and drier air in the region through Wednesday will result
in mainly VFR conditions. River Valley fog will still be possible at
night as winds diminish and cool air mass decouples. There is still
some model differences regarding a low pressure system forming from the
Gulf Coast later this week. Several models show moisture increasing
overnight Wednesday through Thursday evening which may result in
periods of IFR/MVFR ceilings and visibilities.