Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
107 PM EDT Wednesday Aug 27 2014
high pressure will be over the Middle Atlantic States this afternoon.
A weak cold front will move south into the region tonight and will
stall across our area through Thursday and Friday...providing the
focus for occasional showers and thunderstorms. The front will
lift north again on Saturday as a warm front.
Near term /through tonight/...
as of 1140 am EDT Wednesday...
Expect mainly sunny skies this afternoon. Models continue to show
potential for some rain showers/thunderstorms and rain to form across the eastern Ohio Valley
and shift southeast toward the Alleghany Highlands later this afternoon.
Airmass in the region remains pretty dry so not expecting much in
the way of coverage but added isolated threat in Bath/Greenbrier
region. Bumped highs a couple degrees as readings out east already
with 4-5 degrees of forecast highs and with full sun think middle to
upper 80s is possible.
Previous valid discussion...
With dew points increasing and some cloud cover in the
evening...low temperatures will be near the mav
guidance...slightly milder than this morning.
Short term /Thursday through Friday night/...
as of 245 am EDT Wednesday...
Cristobal will exit the picture tracking away from the US
Thursday. A weak cool front will then have a chance to move south
of the forecast area Thursday afternoon/night. This boundary may
develop a surface reflection over North Carolina which could
generate isolated showers and thunderstorms during the afternoon.
With limited moisture and a cap overhead...any showers than form
will have a short life span and fade with sunset.
Thursday night...surface high pressure will be centered over New
England and wedge as far south as North Carolina. This surface
ridge will drift off the New England and middle Atlantic coast on
Friday. Meanwhile Friday...an upper level ridge will be centered
over the southeastern US stretching north into the Ohio Valley and
middle Atlantic region. The forecast area will be on the northern
periphery of this ridge. We will then need to keep an eye over the
Tennessee Valley to see if any short waves will track over the
region. For now...models are not showing any significant short
As high pressure drifts off shore...retreating boundary and
southeasterly upslope component will likely trigger afternoon and
evening convection Friday afternoon. The cap is expected to weaken
over the mountains to increase the chances for convection to
develop. This convection will then drift east to the foothills and
Piedmont late in the afternoon and into the evening. In this pulse
storm environment...a few storms could become strong to severe
with damaging winds the primary threat.
Long term /Saturday through Tuesday/...
as of 210 PM EDT Tuesday...
Airmass change in store as 500 mb ridge builds across the southeast then
shifts eastward through next week. This is going to provide hotter temperatures
for Labor Day weekend with increased humidity. Trough will be
situated over the Midwest Sat...shifting eastward into the Great Lakes
Sunday while shearing out. Frontal boundary is going to lay across
the Ohio Valley. Moisture surging northward from the Gulf Coast should
start tracking closer to our area. Sat will be the driest day for
the official end to the Summer season...but isolated storms are
possible in the mountains
Sunday is going to be a bit wetter as the front tracks closer but
still it looks scattered instead of widespread...best coverage over
the mountains so for those planning outdoor activities be aware for both
storms/lightning and hotter temperatures.
Labor Day itself should be stormy although front will be north of
US...but upper shortwave may pass across the central Appalachians
inducing better lift with increased moisture. The upper heights
flatten somewhat as well. Highs Monday are going to still be very
warm with lower 80s mountains to near 90 southeast...though
increased humidity and SW flow will hinder a big rise in temperatures.
By Tuesday...we are still seeing somewhat flattening of the ridge
north of US...with next upstream trough moving across the upper
Mississippi Valley. Looks more like diurnally driven convection
though 00z European model (ecmwf) shows weak impulse moving across the area Tuesday
Aviation /17z Wednesday through Sunday/...
as of 100 PM EDT Wednesday...
Early afternoon satellite loop shows mainly clear skies over the taf
sites with some cumulus starting to pop to our north...along and ahead of
an approaching cold front. Mesoscale model relative humidity fields seem to capture the
moisture fields well so will lean heavily on them through this taf
period. Believe with loss of heating...any broken ceilings of cumulus will become
scattered during the evening...setting up decent rad cooling early. This
should make for another round of nocturnal fog/stratus mainly west of
the Blue Ridge overnight. Will have to keep an eye out for a surge of
broken ceilings coming in as northwest winds generate some upslope west of the ridge...
and possibly limiting development of IFR/LIFR conditions. A period of
broken ceilings seems likely tomorrow morning as lingering moisture combines with
heating. Winds will generally be north/NE early...with a bit of enhancement to
the east...then becoming northwesterly tomorrow.
the cold front will settle across the central Appalachians
Thursday. Spotty showers and thunderstorms will be possible into
the weekend as weak disturbances pass along the boundary. Brief
periods of sub VFR conditions are expected with the precipitation.
as of 1130 am EDT Wednesday ...
The visibility sensor at kdan...Danville Regional
Airport...remains out of service. A part has been ordered but
appears repairs will not be done until this Friday.