Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
954 PM EDT Wednesday Sep 2 2015
our region will remain situated in a hot and humid weather pattern
for this time of year...with daily chances of isolated to scattered
showers...with a few storms...through at least Friday. A backdoor
cold front will cross the region Friday night into Saturday...and
bring an increased coverage of precipitation in advance of it late
Friday into Friday night. Drier and cooler air will work its way
into the area for the latter half of the weekend into the start of
Near term /through Thursday/...
as of 950 PM EDT Wednesday...
Keeping a few showers in the forecast until midnight from Halifax to
Yadkin...but have it dry overnight. Upper vorticity now centered over
the Shenandoah Valley allowing more lift ahead of it into eastern
VA/NC. There are some showers across Ohio which models try to
track southeast toward southeast WV toward morning...but fade it out before
Still expect fog to form overnight in the river valleys.
Previous valid discussion...
On Thursday...patchy morning fog will dissipate by 10am at most
locations. Another upper level disturbance will approach from the
west during the afternoon hours. This one looks to have a track a
little farther south than the system of today. This will have the
impact of bring scattered coverage to northwestern parts of the
area by the afternoon...with isolated coverage expected east to at
least the crest of the Blue Ridge. Isolated coverage across the
Piedmont will occur later in the afternoon. Temperatures will
continue with readings above normal. Highs in the mountain will
range from the low to middle 80s with upper 80s to lower 90s across
the foothills and Piedmont.
Short term /Thursday night through Saturday/...
as of 315 PM EDT Wednesday...
500 mb heights continue to rise over the northeast United States
through Friday night. But at this same time the short wave coming
out of Minnesota tracks over the Great Lakes will contribute to an
elongated region over lower heights from the Great Lakes to the
Carolinas...between two parts of the upper ridge by Friday.
Friday will still have maximum temperatures above normal but by
Saturday morning northeast winds brings in an air mass with 850 mb
temperatures around +14. These cooler temperatures combined with
upslope clouds on eastern slopes will keep maximum temperatures at
or just below normal on Saturday.
Long term /Saturday night through Wednesday/...
as of 100 PM EDT Wednesday...
A bulk of the upper ridge remains over the Southern Plains while
another piece moves across the northeast United States. Sunday and
Monday models still showed relatively lower height over the
southeast United States. During the week the upper ridge flattens
and by Wednesday...a deep trough has progressed into the central
Dry airmass remains over the area Saturday night and Sunday. Models
begin to bring low level moisture back into the region on Tuesday
night and Wednesday. By Tuesday...at the surface...the parent high
moves far enough offshore that the part of the high over the central
Appalachians will be very weak. Change in upper pattern will set up
deeper southwest flow over the region on Wednesday ahead of the
approaching upper trough. Better coverage of pre-frontal showers and
thunderstorms will not be until Wednesday.
Will have a mainly dry forecast for Saturday night through Tuesday
in all but the far southwest counties of the forecast area.
Temperatures will be close to normal on Saturday and Sunday but will
then gradually warm through Wednesday.
Aviation /02z Thursday through Monday/...
as of 725 PM EDT Wednesday...
Upper wave over the Alleghany Highlands early this evening shifts
southeast off the NC coast by Thursday...while another piece of
energy moves from the Ohio Valley to the smokys. At this time...the
terminals in line for at least vcsh this evening are lyh/Dan and
lwb. Radar shows the better convection with mesoanalysis depicting
the better instability over the Piedmont along/east of lyh/Dan. A
smaller area of showers and storms lies east of crw heading southeast
toward lwb...and should weaken toward 01z...so kept it vcsh.
Overnight...the rather humid airmass with less clouds will induce
fog formation...especially the typical lwb/bcb locations.
Elsewhere...the fog if any forms will be MVFR.
Thursday...expect VFR conditions. However...in the
afternoon...showers and storms will fire up over mountains...with
blf/lwb more in line for showers or storms...but still only
scattered coverage. At this time...have them vcsh after 18z...and ceilings
will mainly be VFR 4-6kft.
Extended aviation discussion...
Will see a weak flow pattern with an upper trough extending from
east-west over our area Friday into Sunday. We will see the low
level flow turn more easterly in time. As of now...the terminals
will be VFR during the day...with possible MVFR or worse with fog
at night into Friday night. The easterly flow expected by Saturday
will bring lower clouds in and potential for MVFR ceilings at least
for the mountains...and low end VFR roa/lyh/Dan. With this upper
trough there will be daily threat of showers...so sub VFR in these
By Sunday-Monday the weak trough aloft moves over the southeast
coast while upper ridging elongates over the middle Atlantic. We will
see some drying take place so VFR should occur Sunday-Monday with
the still a threat of fog at night at bcb/lwb.
short term...air mass
long term...air mass