Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
122 PM 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 100 PM EDT Sunday...
kfcx 88d showed some scattered showers moving into the western
portions of forecast area. Adjustment probability of precipitation across the far west to
account for this convection this afternoon. Modified temperatures
with latest observation and trend. Raised high in the east a few degrees
with sunshine. More changes this afternoon.
As of 933 am EDT Sunday...
made some minor adjustments in temperatures and cloud cover for
this morning. Low pressure center off the North Carolina coast
this morning will lift north into tonight...as cold front in the
Ohio Valley approaches from the west. The hrrr...NAM and hiresw-
arw still keep the best chances of convection in the west. More
changes later this morning...
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 Wednesday 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 /Thursday through Saturday/...
as of 100 PM EDT Sunday...
A strong surface high over the NE states on Thursday will slowly
drift westward to the Great Lakes by the weekend. This will lead to
a prolonged easterly flow across the region. High temperatures will
be 5-10 degrees below normal ranging from the middle to upper 60s
across the mountains to lower 70s east of the Blue Ridge.
Models are starting to agree on a weak upper level disturbance
forming across the southeast states late in the week...however there is
still major differences on placement which will affect how much
moisture can get pulled up into the region. The GFS continues to be
much drier than the European model (ecmwf). Due to the model differences...only
slight chance probability of precipitation in from the Blue Ridge eastward.
Aviation /18z Sunday through Thursday/...
as of 122 PM EDT Sunday...
A cold front along the Ohio River will drop southeast this
afternoon into tonight. Scattered showers and isolated
thunderstorm in the mountains will spread east this afternoon into
tonight. Low level winds should increase with the approaching
front...and gusts 20-25kts are possible this afternoon into this
evening. High confidence that a majority of precipitation along
the front will cross the region between 18z/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. MVFR ceilings are
expected at kblf and klwb overnight into Monday morning. Drier air
will push south across the region Monday afternoon into Monday
High confidences on ceiling and visibilities during taf period.
Medium to high confidence on wind during the period.
Extended aviation discussion...
High pressure and drier air in the region Monday night through
Thursday will result in mainly VFR conditions. River Valley fog
will still be possible at night.