Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
737 am EDT Tue Sep 26 2017
high pressure over the eastern United States will continue to
bring warm and dry weather to the region through midweek, while
Hurricane Maria stays just off the East Coast. A dry cold front
will move through the Appalachians and mid Atlantic region on
Thursday, with much cooler weather for the end of the workweek
into the weekend.
Near term /through tonight/...
as of 725 am EDT Tuesday...
Cirrus has thinned out across the mountains this morning and
more patchy fog has formed in the mountain valleys but this
should dissipate very quickly within an hour or so after
sunrise. Low stratus can also been seen on nighttime satellite
microphysics curves barely sneaking into the far eastern corners
of Halifax and Charlotte counties, and may try to get into parts
of Caswell, but westward trend seems to have slowed and once
heating of the day gets going and based on model guidance,
expect this to retreat and mix out during the mid morning hours.
Otherwise no other changes to today's forecast.
Previous discusison as of 412 am EDT Tuesday...
While generally dry and warm high pressure remains over the
appalachian region sandwiched in between a cold front across the
Midwest and Hurricane Maria off the Carolina coast, there has
been a slight increase in low level moisture with some areas of
stratocumulus over parts of the mountains, as well as moving in
across the Piedmont with the gradient west of Maria. Patchy fog
has begun developing early this morning where breaks in the
clouds are. Lower stratus just to the east of our area may sneak
in across parts of the Piedmont today, but does not look like it
will make much progress before the heating of the day helps to
mix it and it breaks up or drifts back east. Meanwhile, cirrus
over the mountains should remain thin enough to allow daytime
cumulus to form with dew points in the 60s and afternoon
temperatures reaching into the 80s again except on higher
ridges. This is about 10 degrees or so above average for this
time of year. With some weak convergence along Blue Ridge and
over higher peaks on the west side of Appalachians, would not be
totally surprised if an isolated shower were to form in one or
two spots, most likely along southern Blue Ridge or in southeast WV
from Flat Top to wrn Greenbrier co. Certainly not expecting any
thunder, and most likely no showers will form at all given dry
air aloft. Did add a couple small areas of slight chc pops
however for a few hours this afternoon however.
Otherwise weak Hurricane Maria will remain far enough offshore
to have minimal effects on our area as it continues to move
slowly north through today, other than keeping a northeast wind
direction with speeds in the 10-15 mph for Piedmont areas and
maybe a gust or two approaching 20 mph. Not all that unusually
for late September in any case. Does not look like any
peripheral showers will even reach into our Piedmont areas.
By tonight despite the fact that Maria still will not quite be
ready to shift eastward and away from the coast, low-level
clouds on the far western periphery are expected to pull east
and dissipate per most model guidance and some weakening of the
system, and thus do not expect any low-level cloudiness to
persist over the Piedmont, but more likely to develop in spots again
in mountain valleys, along with patchy fog. This an almost
routine occurrence for this time of year. Mild low temperatures
expected once again.
Short term /Wednesday through Friday night/...
as of 300 am EDT Tuesday...
During this portion of the forecast, a ridge of mild and dry high
pressure will be situated across the area on Wednesday, all while
hurricane/Tropical Storm Maria moves north through the western
Atlantic east of the North Carolina coast. By Thursday, Maria will
be jogging northeast and increasing in speed as a tropical storm,
while a cold front heads southeast across the region. The front will
be very moisture starved, and currently, at best we are anticipating
increased cloud cover across the mountains with little if any
The biggest impact the front will have will be a notable change in
airmass. We will quickly transition from above normal and more humid
than normal conditions, to a pattern that is only slightly above
normal on Friday and Friday night, along with lower humidity
readings. Somewhat windy conditions are anticipated behind the front
Friday into Friday night. Gusts of 25 to 30 mph will be possible at
the higher ridge tops, with weaker gusts across the mountain valleys
and Piedmont region.
Long term /Saturday through Monday/...
as of 203 PM EDT Monday...
500 mb trough digs across the Great Lakes into our area Friday into
Saturday with high pressure starting to shift southward from the
Great Lakes into Sunday. Will be a dry/cooler with temps close to or
below normal. Later Sunday into Monday the flow turns more northeast
as the high wedges southward. Should start to see clouds increasing
Monday especially as the flow turns more east off the ocean. At the
moment confidence in any showers is low, so keeping pops below 15
Aviation /11z Tuesday through Saturday/...
as of 735 am EDT Tuesday...
Early morning IFR conditions at klwb as well as MVFR at kbcb are
expected to lift by 13 or 14z. Otherwise VFR conditions expected
at all taf sites today with high pressure over the NE U.S.
Bringing light northeast winds to the region, except a little
gusty this afternoon at klyh and kdan with hurrican Maria off
the Carolina coast. IFR stratus will be on the doorstep of kdan
but should remain to the east today. A few high cirrus clouds
across the entire region, with some cumulus by this afternoon
in the mountains. Very slight chance for an isolated afternoon
shower on ridges to the west of klwb and maybe near kblf but if
these can even form will unlikely move into vicinity of these
airports so certainly not Worth including in tafs.
Lower cigs may develop again in the Piedmont late tonight into
early Wednesday as Maria makes it closest approach offshore of the
Carolinas. Latest guidance suggests a swath of VFR to MVFR cigs
may advect inland again on increasing northeast flow with at
least a period of sub-VFR possible early Wednesday but most
likely this will again remain east of kdan and klyh. Patchy
Mountain Valley IFR fog likely again by late tonight and early
Extended aviation discussion...
Maria should exit farther offshore Wednesday night into Thursday
ahead of a cold front that looks to cross the region from the
west during the day. Front appears mainly dry with just a band
of upslope aided low clouds possible behind the front Thursday
before much drier Post frontal air swings in on northwest winds
later Thursday into early Friday. Strong high pressure then
follows the boundary with continued VFR outside of added upslope
clouds far west Friday through Saturday.