Area forecast discussion
National Weather Service Blacksburg Virginia
458 am EDT Friday may 24 2013
Synopsis...
A strong cold front will continue to make its way across our area
this morning...ushering cooler and drier air in from the
northwest. High pressure building in with the front will keep the
unseasonably cool air in the area through the weekend. A warm
front will lift north from the Gulf Coast early next week...followed
by strong high pressure bringing more Summer like weather by middle
to late week.
&&
Near term /through tonight/...
as of 400 am EDT Friday...
The weather pattern through the weekend...especially today...will
look like something we more commonly seen during the winter as
opposed to late may...as a deep upper level low passes from the
Great Lakes toward lower New England. Surface observations
indicate that significantly cooler and drier air is working in
from the northwest as a cold front crosses our area this
morning...and radar indicates upslope rainshowers falling from the
North Carolina mountains into southeast West Virginia. Models are
in decent agreement that these showers will diminish through early
afternoon...with cloud cover breaking up from east to west in the
downslope northwesterly wind flow.
The larger concern however will be strong wind gusts as high
pressure builds in on an 8 mb pressure gradient. With clouds
expected to scatter along the Blue Ridge by late morning...expect
we will see stronger winds aloft mix down to the surface...where
ridges above 3000 feet can see 40 to 50 miles per hour winds through the day.
Wind speeds may reach as high as 35 miles per hour elsewhere.
Highs for today will be significantly cooler...and not expected to
warm much from early morning lows across the mountains. On top of
that...the strong wind gusts will add an extra chill to the
air...so it will be a good idea to keep a sweater or light jacket
handy. Afternoon highs will range from the middle/upper 50s across
the mountains...to around 70 in the North Carolina Piedmont.
This evening and tonight...wind speeds will diminish by sunset as
the pressure gradient relaxes...and temperatures will drop quickly
with mostly clear skies expected for the area. Will be looking for
overnight lows to fall into the upper 30s further east of the
Blue Ridge...and into the low/middle 30s across the mountains. Wind
speeds will remain strong enough through the night to prevent
frost in all but the most sheltered locations...however believe
that enough cold air will reach into Bath and Greenbrier counties
to warrant a freeze warning...especially in the higher elevations.
&&
Short term /Saturday through Tuesday/...
as of 400 am EDT Friday...
Deep upper low and associated anomalous cold 850mb temperatures will begin
to lift to the NE Saturday as upper flow remains slowly progressive
and a broad upper ridge begins to spread from the central U.S. Into
the eastern U.S. The 850mb 0c isotherm will lift NE toward the District of Columbia
metropolitan area by Sat evening. Temperatures will remain well below
normal again Saturday...although increased sunshine...especially
across the mountain areas...will help temperatures recover some from
an unseasonably cold morning with lows of freezing in the higher
elevations of the alleghanys...to widespread middle and upper 30s
across much of the western part of the County Warning Area...especially elevations
above 2000 feet. Expect afternoon temperatures to recover into the 60s west
and lower 70s Piedmont...with some 50s definitely hanging on across
the higher elevations of Bath and Greenbrier counties. Most of the
medium range models depict potential for high clouds to spread from
the plains southeastward toward our region in increasingly strong
middle-level warm air advection. This will continue and increase into Sun morning
which should limit radiational cooling. Strong warm air advection aloft should keep
higher elevations warmer as well. Thus...do not see any need for
frost/freeze headlines Sun morning at this time. Temperatures will
continue to recover Sun afternoon...but likely remain several
degrees below normal again. No precipitation expected through the weekend.
By Monday into Tuesday...a broad subtropical ridge continues to spread into
and amplify from the middle-south into the Midwest. With the upper
trough still lingering across the central-North Atlantic...northwest flow
aloft will prevail across our region. Our attention will focus on a
series of northwest flow disturbances slated to ride over the building
ridge and toward the middle-Atlantic region...especially in the late
Monday-Tuesday period...before the ridge amplifies enough to shove this
conveyer belt of disturbances further north toward PA/NY. The air
mass across the region will become increasingly moist and
unstable...especially Tuesday...as temperatures rise into the 70s and lower 80s
with dewpoints rising into the 50s and low 60s. Will need to watch
for northwest flow/mesoscale convective system thunderstorms and rain activity developing across the upper Midwest/Ohio
Valley to ride southeast along the middle-level baroclinic zone. Not expecting
much quantitative precipitation forecast concern with this activity as the surface air mass will be
slowly recovering from the abnormally low dewpoints in place sun-
Monday...but strong thunderstorm wind gusts will be a
concern...especially as the activity downslopes toward the Roanoke
valley. Still quite a ways out there...but the models have been
pretty consistent in advertising this pattern...so it will need to
be watched. Temperatures should return to normal levels by Monday-
Tuesday...and likely above normal beyond that.
&&
Long term /Tuesday night through Thursday/...
as of 350 PM EDT Thursday
Looks like we will trade the cool upper trough for a Mammoth Ridge
that will overtake the eastern Continental U.S. By Wednesday. For Wednesday
and Thursday...with the passage of a warm front...it will be back
to really warm temperatures and higher humidity with the threat
for airmass showers and thunderstorms mainly during the peak
heating hours.
&&
Aviation /09z Friday through Tuesday/...
as of 200 am EDT Thursday...
Thunderstorm activity has exited the area for the remainder of
the weekend...and will now contend with a strong cold front that
will cross the area this morning. With the cold air building in
behind the front...will see a short period of low MVFR/IFR
ceilings from roa westward...that will gradually improve through
sunrise. By late morning...expect to see low clouds scatter for
these airports...resulting in VFR conditions through the remainder
of the day. Further east...lyh and Dan are expected to remain
VFR.
The main concern for this taf period however will be gusty winds
as the pressure gradient increases to around 8 mb across the
forecast area after sunrise. As such...will be looking at wind
gusts as high as 30 kts for bcb...blf and lyh....and up to 25 kts
for Dan and lyh. Wind direction will be near perfect for terrain
induced funneling at roa...and would not be surprised to see gusts
top out near 40 kts during early afternoon.
Expect to see wind speeds diminish during the evening...however
the pressure gradient will remain tight as low pressure off the
coast of New England deepens. As such...wind gusts across the
mountains will remain as high as 15 to 20 kts through Friday
night... before wind speeds diminish on Saturday.
High pressure to keep US VFR through the weekend. Moisture
increases again next week as the surface high moves east and the upper
ridge strengthens over the Mississippi Valley. Will be getting to
more humid weather again with some thunderstorm threat by Tuesday
and fog issues at night in the valleys.
&&
Rnk watches/warnings/advisories...
Virginia...Wind Advisory from 8 am this morning to 7 PM EDT this evening
for vaz009-012>017-022.
Freeze warning from 2 am to 8 am EDT Saturday for vaz020.
NC...Wind Advisory from 8 am this morning to 7 PM EDT this evening
for ncz001-002-018.
WV...freeze warning from 2 am to 8 am EDT Saturday for wvz045.
&&
$$
Synopsis...nf
near term...nf
short term...rab
long term...PM
aviation...jh/nf
