Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
323 PM EDT Thursday Sep 18 2014
high pressure over the area will weaken and slide east offshore
tonight. A weak cool front will drop southeast across the region
this evening into tonight. Strong high pressure will build to the
north late tonight into Saturday before passing offshore on Sunday.
A cold front will cross the area from the northwest on Monday
bringing a better chance of showers to start the week.
Near term /through Friday/...
as of 250 PM EDT Thursday...
Broad upper-level trough will remain over the region tonight into
Friday...while a weak upper-level disturbance passes through in the
flow aloft. A weak cold front will slide south across the region
this evening into tonight.
Showers should drop southward and fade this evening into tonight as
the onset of a deepening east to southeast flow develops in response
to strong high pressure building in from the north. Moisture banked
up along the mountains with depth to support mention of spotty -ra
and certainly drizzle/fog by daybreak. Cool tonight with low
temperatures ranging from around 50 degrees in the mountains to near
60 degrees in the southeast.
A broad area of high pressure will move over New England and wedge
south down the East Coast on Friday. An easterly flow will create
areas of fog and drizzle along the eastern slopes of the Blue Ridge
into the early afternoon. Although limited...afternoon heating
combined with mixing may erase drizzle/fog through the
afternoon...while some light showers developing over the region into
the evening. Increased cloud cover for Friday and raised probability of precipitation
especially along the southern Blue Ridge. Friday afternoon
temperatures will be colder than normal with areas keeping
precipitation through the day. Lowered high temperatures on Friday
with readings from the middle 60s in the mountains to the lower 70s
in the Piedmont.
Short term /Friday night through Sunday night/...
as of 250 PM EDT Thursday...
Model trends have sped up the next front arriving Sunday now instead
of Monday. Until then...expect the high pressure over the New
England coast to wedge southwest into our area Friday night into
Saturday. Another cloudy sky can be anticipated across the Blue
Ridge and either side late Friday night...but skies clear out
A cold front shifts southeast over the region Sunday...with main
lift and shortwave energy staying across the Ohio Valley. This
shortwave then pivots southeast across WV Sunday night..and could
bring a few showers here. May see enough instability with the front
Sunday to allow for thunderstorms. Overall chance of precipitation is
20/30...higher into WV.
Temperatures this period will modify to seasonal levels...with lows in the
50s and highs in the 70s...except lower to middle 80s southeast Sunday.
Long term /Monday through Thursday/...
as of 200 PM EDT Thursday...
This period is shaping up to be dry and seasonal. Another shortwave
drops southeast across the Tennessee Valley Monday and could bring isolated
showers to the entire areas as flow backs aloft some. Then high
pressure across the Midwest pushes east over the middle Atlantic
Tuesday- Wednesday. Temperatures behind this system early next week will cool down
some...but not looking as chilly as earlier thought...with 800 mb
Highs will run from the 60s west to 70s east...with lows mainly in
the 40s...with some 50s across the Piedmont.
Aviation /20z Thursday through Tuesday/...
as of 140 PM EDT Thursday...
Scattered to broken MVFR clouds this afternoon into tonight. Heating this
afternoon will result in some buildups of cumulus across the mountains
where isolated MVFR afternoon rain showers are possible. Coverage will be
to limited to include in taf locations.
Cumulus fields scattering out by evening underneath a leftover middle
deck. This supports mainly VFR into early tonight as the weak
boundary shifts south and high pressure starts to build in from
the north. Flow turns more easterly later tonight as stronger high
pressure builds in with widespread MVFR/IFR ceilings likely developing
after midnight with the onset of stronger wedging. Think some
drizzle also possible along the Blue Ridge espcly kroa/kbcb near
dawn with patchy dense fog mixed in and across the deeper western
valleys late. Isolated MVFR convection and clouds are possible
Friday with the light upslope flow.
Medium to high confidence in ceiling and visibilities during the
taf period. High confidence in winds during the period.
Extended aviation discussion...
High pressure will dominate the weather through the end of the
week with little or no precipitation. Expect mainly VFR
conditions outside any fog at night and potential for some low
level stratus along and east of roa/bcb...though the high
pressure should be strong enough to keep moisture limited.
Presence of subsidence inversion aloft will likely result in
cloud layer persisting between 040-060kft...so it will not be
Next upstream trough and front expected to arrive by early next
week with a threat of showers mainly late Sunday night into Monday.
May see some MVFR ceilings/visibilities within a band of showers during that
period but appears most of the time will continue to see VFR.