Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
742 am EDT sun Sep 21 2014
low pressure was over Michigan with a cold front trailing into the
middle Mississippi Valley. This front will move east today and
tonight...and will reach the East Coast by Monday morning. Monday
through Thursday...a large high pressure system will cover much of
the eastern United States.
Near term /through tonight/...
as of 400 am Sunday...
Satellite pictures and surface observations showed that fog had
developed in the new and Greenbrier River valleys this morning.
The fog will lift shortly after sunrise.
Timing of the front remains similar in the guidance as past few
runs. Bulk of showers and thunderstorms will come through the
forecast area between 2pm/18z and 8pm/00z. Amount of instability
this afternoon will depend on how much heating there is...how fast
the clouds arrive from the west. Models have enough cape and
surface heating to support thunderstorms. Models also confine a
majority of the precipitation to along and west of the Blue Ridge.
This seems reasonable with the low level winds starting from the
north this morning and backing to the west ahead of the front as
high pressure over the area weakens.
The front comes through the forecast area between 00z/8pm and
06z/2am. Decent pressure rises behind the front with 850 mb
temperatures dropping to around +6 in southeast West Virginia by
Expecting some low level moisture in the western upslope area
after midnight...but BUFKIT forecast soundings showed the moisture
will be shallow. East of the Blue Ridge will clear out late
Short term /Monday through Tuesday night/...
as of 300 am EDT Sunday...
An upper level trough will pivot across the region with northwest
flow and low level moisture keeping clouds banked up against western
slopes through Monday morning. Once this trough axis tracks to the
middle Atlantic coast during the afternoon...dry air will erode
mountain clouds with clear conditions continuing through the rest of
the period. Downslope flow is expected east of the Blue Ridge to
keep clear skies through the entire period.
Following the passing of the upper level trough...a surge of cooler
drier air will move over the area. Dew points will drop into the 40s
Monday afternoon and continue to lower into the 30s across the
mountains Monday night. Overnight lows will range from the upper 30s
in mountain valleys to the upper 40s in the Piedmont. Temperatures
will run 5f-10f cooler than normal Monday and Tuesday afternoon.
Also Monday...pressure rises will bring breezy and gusty conditions
to the area...especially along the Blue Ridge. Gusts along the Blue
Ridge could top out at 30 miles per hour.
Long term /Wednesday through Saturday/...
as of 100 PM EDT Saturday...
The extended period is dominated by a 1032mb surface high that
starts in southern Quebec on Wednesday and will slowly drift south
over the NE states by Saturday. The result of this will be an
easterly wedge flow through the entire period. There is significant
differences in placement of a middle level closed low by the GFS and
the European model (ecmwf) to our west...which will impact how much moisture can get
pulled into the region. At this point trended toward HPC and the
drier GFS solutions and kept just low chance probability of precipitation along and east of
the Blue Ridge from Thursday through the end of the period. Any
precipitation that does fall will likely be just patchy drizzle with little
to no accumulation.
Went below guidance for high temperatures as the models are typically too
warm with an easterly flow. Expect surface highs of middle to upper 60s
across the mountains to low 70s east of the Blue Ridge.
Aviation /12z Sunday through Thursday/...
as of 740 am EDT Sunday...
Satellite pictures showed a clear sky over central and western
Virginia with clouds in the east. Fog was observed along the New
River and Greenbrier River...resulting in LIFR visibilities at
klwb and kbcb.
The fog will dissipate by 14z/10am....but moisture advancing
ahead of an approaching cold front will bring clouds into the
mountains by late morning. Scattered showers will also develop in
the mountains during the afternoon. Low level winds increase with
the approaching front...and gusts 20-25kts are possible by this
afternoon. High confidence that a majority of precipitation along
the front will cross the region between 12z/2pm and 00z/8pm and
that most of the precipitation will be west of the Blue Ridge.
Winds become west to northwest behind the front tonight. Models
were suggesting some low level moisture will bank up against the
western slops of the Appalachians late tonight. Have added MVFR
ceilings at kblf and klwb after midnight.
Extended aviation discussion...
High pressure and drier air in the region Monday through Thursday
will result in mainly VFR conditions. River Valley fog will still
be possible at night.
near term...air mass