Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1059 PM EST Sat Jan 31 2015
high pressure over the middle Atlantic region will move southeast and
offshore by morning. Low pressure was developing over the central
rockies and will track into the Ohio Valley Sunday night then off
the New Jersey coast on Monday. This system will push a cold front
through our region on Sunday night...which will be followed by high
pressure for Monday and Tuesday.
Near term /through Sunday/...
as of 1040 PM EST Saturday...
Clouds increasing from the west but still thin overall in the
east. Anticipate coverage to increase with skies becoming overcast
across the County Warning Area through dawn. Temperatures had sunk into the 20s in the
valleys and rural areas but once clouds move across temperatures will
slow and steady out...and may even rise in the west toward morning
across the higher elevations per increasing southerly flow.
The previous forecast had this in mind and only minor tweaks are
needed to the temperatures and sky cover through the night with no precipitation
expected...until very light precipitation hugs northwest Greenbrier by 7 am.
Previous valid discussion issued at 4 PM...
Have left a low probability of precipitation in the far northern
County Warning Area late tonight and early Monday. BUFKIT showed a
weak warm nose so the most likely precipitation type will be snow
Have slowed down the precipitation expected ahead of the cold front
on Sunday. Timing on the guidance does not have any precipitation in
the forecast area before 21z/4pm. With all the cloud cover on Monday
have stayed with cooler met guidance for afternoon highs.
Short term /Sunday night through Tuesday night/...
as of 345 PM EST Saturday...
An upper level trough coming across the Mississippi Valley and into
the Ohio Valley will push a surface wave over the southern Ohio
Valley Sunday evening...near Pittsburgh early Monday morning...then
off the middle Atlantic coast by noon. This northeast track across the
Ohio Valley will keep the area in the warm sector through much of
Sunday night into Monday morning. Strong warm air advection will
send 850 mb temperatures to near 8c...keeping ptype as rain for much of
the area into early Monday morning. The cold front will track over
the mountains by sunrise Monday with higher elevations changing over
to snow. By noon...the front is east of the Piedmont and mountain
temperatures begin to crash through the day. As colder air filters
into the region in the afternoon...moisture will become shallow with
any snow accumulations confined to western slopes of southeastern
West Virginia to northwestern North Carolina mountains.
Accumulations along western slopes will range from 1-3 inches
across western Greenbrier to up to two inches across higher
elevations of northwestern North Carolina. If snow bands are able
to setup Monday afternoon...the New River valley and Alleghany
Highlands could see a strip of an inch but in general...less than
a half of an inch. High pressure builds over the Ohio Valley by
Monday evening...therefore snow showers and flurries will not last
long past sunset.
Strong pressure rises (8-12mb/6hrs) behind the front will bring
windy and gusty conditions to the area Monday afternoon into Monday
night. Couple these pressure rises with strong cold air advection
and a 50kt or higher northwesterly low level jet could bring high
wind warnings to counties along and west of the Blue
Ridge...advisories elsewhere. One hitch in this strong wind event is
cloud cover. If clouds remain thick enough once we go into upslope
snow showers...these winds will not be able to mix down. With this
in mind and being a 4th-5th period event...will highlight wind
potential in hazardous weather outlook.
Once every thing blows through Monday night...high pressure takes
residence over the area for a couple of days. Warmest temperatures
likely Sunday night into Monday morning...then drop 30f or so Monday
night into Tuesday morning. Air temperatures Tuesday morning ranging
between 5f-15f above across the west to the lower 20s east. We
expect monday's high winds to drop off by Tuesday morning with
wind chills across the mountains remaining above zero.
Long term /Wednesday through Saturday/...
as of 300 PM EST Saturday...
Expect to start Wednesday with southwesterly winds established
across our area as weak upper level ridging sets up ahead of an
approaching upper level trough and associated cold front. Despite
increasing clouds during the afternoon...we can look forward to a
mild day as afternoon temperatures climb into the middle/upper 40s
across the mountains...and reach to the low/middle 50s east of the Blue
Weather forecast models have not changed much today concerning the
approach of the upper trough and its support of development of a low
pressure system along the southeast coast Wednesday night. As
such...expect the cold front approaching from the northwest to push
rapidly across our area late Wednesday evening...followed by high
pressure passing across the Great Lakes into New England...with the
high then building southward across the middle Atlantic to wedge
against the eastern face of the Appalachians by Thursday afternoon.
Meanwhile...the low along the southeast coast will gradually deepen
and drift northward...radiating moisture inland across the southeast
states into the middle Atlantic.
The big question is to what degree that the coastal low will affect
our weather for Thursday. The GFS forecast model is most aggressive
in pushing moisture across our area...with the Canadian model
similar but not quite as aggressive. On the other end of the
spectrum is the European model (ecmwf) model which does not develop the coastal low
as deeply and therefore keeps our area dry in the wake of the cold
front. Right now...am leaning toward the GFS/Canadian solution...
which will bring light wintry precipitation to our area for
Thursday into Thursday night. All models agree that atmospheric
temperatures will be cold enough for almost exclusively snow for our
entire area. Because of the wide range in precipitation amounts
within the models...have no confidence at this point in the amount
of snow we would receive...but none of the models today are calling
for accumulations that would constitute a winter storm anywhere in
Moisture will decrease late Thursday night as the low continues
northward off the coast. Cool high pressure will pass across the
appalachian chain on Friday...resulting in mostly clear skies and
light winds. Temperatures in the afternoon will remain in the 30s
Aviation /04z Sunday through Thursday/...
as of 1045 PM EST Saturday...
High then middle clouds will increase over the area overnight...with
VFR conditions prevailing along with light winds.
Sunday...southerly flow will increase ahead of a cold front. Still
looking at mainly VFR ceilings around 5-15kft...but will start to see
some MVFR ceilings and light rain heading toward blf/lwb by 00z Monday.
Rain will move across the rest of the area by 06z with MVFR
ceilings at all terminals and MVFR visibilities in the mountains models have
shown some strong low level winds ahead of the front so low level
wind shear may become an issue Sunday evening...but too early for
this storm system over the central U.S. Will track into Ohio
Sunday night and off the middle Atlantic coast Monday
afternoon...swinging a cold front through. This track keeps the
forecast area on the warm side of the system on Sunday night. High
confidence of widespread rain and MVFR or lower ceilings.
Monday...after rain and MVFR conditions in the morning...ceilings
will lift in the afternoon. Expect gusty winds behind this system
with gusts of 25 to 40 knots at higher elevations.
Tuesday and Wednesday...high pressure passes overhead with VFR weather.
Thursday...low pressure moving across the southeast U.S. May
bring sub-VFR conditions and precipitation...possibly snow to the