Area forecast discussion
National Weather Service Blacksburg Virginia
1025 am EDT Tuesday may 21 2013
Synopsis...
low pressure aloft will drift east of the region this morning. A
large low pressure system will track from the Central Plains into
the Great Lakes by Thursday. This system will push a cold front
through the area Thursday...followed by high pressure on Friday.
&&
Near term /through tonight/...
as of 1015 am EDT Tuesday...
northwest winds combined with sunshine will allow visibilities to
improve this morning...thus the dense fog for widespread has
ended. Pocket of fog may linger a hour or so in the deeper
sheltered location. Shortwave over Southside this morning will
travel east into eastern Virginia this afternoon. RUC and WRF
indicated that the best chance for thunderstorms this afternoon
will be along the southern Blue Ridge. Made some minor
adjustments in temperatures and dew points.
As of 500 am EDT Tuesday...
Many locations reporting visibilities one quarter mile or less.
Have issued a dense fog advisory. Conditions will improve after
8am.
Radar showed isolated showers in north central North Carolina this
morning...moving southeast. Have kept chance of precipitation out
of the forecast for this morning. Did leave in areas of fog.
Short wave was over the forecast area early this morning. Most
models have feature moving into eastern Virginia by this
afternoon. RUC and WRF models suggest most likely location for
thunderstorm development will be along the southern Blue Ridge
this afternoon. Then in eastern Kentucky and West
Virginia...moving into our southeast West Virginia counties and
through the northern County Warning Area this evening. Do not
envision more than scattered coverage this afternoon or tonight.
850 mb winds turn to the northwest briefly afternoon following the
short wave then back to southwest for tonight. Northwest flow and
850 mb temperatures around +16 will result in decent warm up for
the foothills and Piedmont...especially in areas that have sun
this morning. Guidance looked reasonable for afternoon highs.
&&
Short term /Wednesday through Friday/...
as of 300 am EDT Tuesday...
Closed upper low and sharp trough over the Midwest will make slow
eastward progress against strong ridge off the Atlantic coast but
eventually will shove a surface front through the County Warning Area Thursday
afternoon. Until then area will remain under southerly flow with
generally abundant moisture but weak to disorganized forcing. May
see a pre-frontal squall line across the Ohio Valley Wednesday afternoon
which will likely be weakening as it approaches far western County Warning Area
Wednesday evening/night. Still maintained at least high chance probability of precipitation in the
mountains ahead of any possible line Wednesday afternoon where
differential diurnal heating and upslope enhancment will be focus
for most likely activity with lower chance probability of precipitation across the Piedmont.
Some storms potentially strong with cape approaching 1000 j/kg but
limited shear should preclude much in the way of severe storms.
Again could be with locally heavy rainfall as precipitable waters remain in the
1.2 to 1.5 inch range ahead of front and storms could be slow-
moving.
Probability of precipitation diminish overnight Wednesday with loss of heating but renewed
convective activity likely on Thursday with passage of surface
front. Not looking for much in the way of severe as best support
well to north of County Warning Area but a few strong storms and more pockets of
heavy rainfall possible. Probability of precipitation decreasing Thursday night and Friday as
drier northwest flow takes over. Left chance probability of precipitation Friday as cooler air aloft
enhances instability lessening trend. Mild temperatures will predominate
ahead of the front with 80s Wednesday and even Thursday but substantially
cooler weather expected behind the front for Friday and beyond.
&&
Long term /Friday night through Monday/...
as of 345 PM EDT Monday...
Both the GFS and European model (ecmwf) are delivering a good intrusion cooler air by
12z Friday with 850 mb temperatures slipping to +5c. The upper trough is forecast
to slide across New England on Friday with cool northwest flow
prognosticated from the Great Lakes to the middle Atlantic.
Cooler northwesterly flow also suggests the air will be dry...thus
have removed all mention of precipitation for the weekend. That said...as
high pressure passes ovhd Saturday and rolls off the East Coast
Sunday...moisture could sneak back in the picture as early as Sunday
afternoon. At this time...will go with an optimistic forecast and just
advertise increasing clouds for Sunday...and hold off on next
opportunity for showers until Monday.
Both Saturday and Sunday mornings look cool with early morning lows
in the 40s in the mountains to the lower 50s in the Piedmont. If
winds decouple and skies remain clear...some of the sheltered
mountain valleys may slip into the upper 30s.
&&
Aviation /14z Tuesday through Saturday/...
as of 730 am EDT Tuesday...
Pockets of fog will continue to lift this morning as winds
increase. Low clouds should lift by late morning.
Isolated to scattered thunderstorms will develop again this
afternoon. Probability at any one Airport is too low to include in
the tafs at this time. Fog formation overnight will be dependent
on which locations get rain this afternoon and which clear out
during the evening.
The region stays in a warm...moist airmass through Thursday.
Areas of fog with MVFR visibilities is likely each night and each
afternoon and evening there will be scattered thunderstorms.
Next front approaches on Thursday with more showers/storms
developing. High pressure and better flying conditions are
expected on Friday behind the front.
&&
Rnk watches/warnings/advisories...
Virginia...none.
NC...none.
WV...none.
&&
$$
Synopsis...air mass
near term...ams/kk
short term...pc
long term...PM
aviation...ams/kk
