Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
322 PM EST sun Dec 8 2013
strong high pressure from New England to the central Appalachians
was flanked by low pressure off the Carolina coast and low
pressure over the Tennessee Valley. Low pressure will remain off
the East Coast through Monday with a cold front trailing through
the southeast United States. Another low tracks along the front on
Tuesday...followed by high pressure Wednesday.
Near term /through Monday/...
as of 300 PM EST Sunday...
First short wave at 500 mb lifts from southern Ohio northeast
tonight with forecast area staying in southwest flow on the east
side of the long wave trough through Monday. At the surface a strong
wedge of high pressure separates from parent high by Monday morning
with low pressure of the middle Atlantic coast and over the Tennessee
Valley. Surface low pressure and cold front move east through the
area Monday. NAM and sref never completely erode The Wedge until the
colder air arrives late Monday. This is slower than on the GFS.
Evaporation and slowly falling dewpoints have resulted in
temperatures cooling into the upper teens in the Alleghany Highlands
to the lower 30s across the North Carolina Piedmont and Southside
Virginia. Only Smith and Tazewell counties had temperatures still in
the middle 30s to near 40. The warmer temperatures above the layer
of cold air advances north this evening...with models showing 850
mb temperatures of +6 to +10 by Monday morning.
After a brief break late this afternoon...more freezing rain is
expected. BUFKIT showed blf/tnb rising above freezing at the
surface during the evening...then all but the northern third of
the County Warning Area climbing above freezing after
midnight...then Lynchburg to Hot Springs not getting to freezing
until after sunrise Monday. This is slightly slower timing then
Precipitation amounts tonight into early Monday morning will also be
critical to how much more ice accumulates. Will stay close to wpc
quantitative precipitation forecast forecast. Best coverage of rain and freezing will be in the
00z/7pm to 09z/4am time frame when the precipitation now in
eastern Tennessee through Louisiana that is associated with a
short wave over Louisiana tracks across the area. This still gives
much of the forecast the area the potential for one quarter inch
total ice accumulation so no changes needed for the winter storm
Short term /Monday night through Wednesday/...
as of 300 PM EST Sunday...
Monday night a wave of low pressure tracks from Alabama up the front
into western North Carolina by Tuesday morning. This will prolong
the probability of precipitation across the forecast area and delay
The Retreat of the moisture...especially in the southern County
Warning Area. Temperatures profile on the GFS was slightly warmer
then the NAM but where temperatures were cold enough for
snow...moisture will be deep enough for Crystal growth. For now
keeping the precipitation type just rain or snow.
Mean trough axis pushes through the region on Tuesday night and
Wednesday. As winds become west over the area on Tuesday
night...deep moisture will exit the region. High pressure centered
in the the Mississippi Valley builds in Tuesday night and Wednesday.
Long term /Wednesday night through Sunday/...
as of 300 PM EST Sunday...
During the Wednesday night through Friday portion of the
forecast...our region...along with most of the north central and
northeast portions of the country will be in a pattern dominated by
long wave trough with the associated upper low situated over Hudson
Bay. Closer to the surface...high pressure will make its way
eastward from the middle-Mississippi Valley to over the central
Appalachians. This will keep US in a below normal temperature regime
along with a dry forecast. A shortwave trough within the main
longwave trough pattern will cross the area Thursday...but any
associated precipitation will be light and remain well north of the
region. The most notable impact on our region will be an increase in
wind speed/gusts as 850 mb winds are prognosticated to be anywhere between
25 and 35 kts. There also will likely be an increase in cloud cover
Wednesday night into early Thursday.
During the upcoming weekend...there is considerable differences
between the operational models in regards to the sensible weather
across our region. What is somewhat common among the solutions is
for the Hudson Bay low to move eastward...and thus allowing for a
more zonal flow across our area. Also...both the GFS and European model (ecmwf)
solutions develop a trough across the central U.S. Along with an
enhanced southerly jet that rounds the base of the trough and
translates into the southeast U.S. And eventually middle-Atlantic
region by Sunday. Increasing cloud cover and chances of
precipitation for our region are also common among the models.
What varies significantly is the track...speed...and any
deepening development of a shortwave trough that progresses along
this southerly jet. The GFS is much slower...and allows a greater
period of time for warm air to advect into the region on southerly
winds ahead of and concurrent with the arrival of the
precipitation. For our area this solution offers the potential of
a rain versus wintry mix forecast. The European model (ecmwf) is much more
progressive in timing...so much so...that the parent upper
trough/low ejects eastward with the southern stream energy and
brings much colder air aloft over the region. All this is
happening while the shortwave trough spawns cyclogenesis off the
coast of the Carolinas and our region would have more of a wintry
mix versus snow forecast. The folks at wpc have opted to follow
close to a ensemble GFS/European model (ecmwf) blend. Our forecast will reflect
numbers close to theirs in regard to temperatures and
precipitation chances...and allow the forecast to be a rain versus
snow forecast with at or sub freezing surface temperatures dictate
the areas of snow. There will be no regard given at this time to
what the low level T/dew point profile will be.
Aviation /20z Sunday through Friday/...
as of 1254 PM EST Sunday...
Ice and low ceilings will hinder aviation operations this
afternoon into Monday. Very high confidence for severe clear icing
at all taf sites today...with one quarter to one half inch ice
Wintry mixture of snow...sleet...freezing drizzle and freezing
rain will continue into this evening...then precipitation will
become freezing rain and rain tonight into Monday morning.
Across the north...where colder air in place closer to
lwb...snow/ice pellets will transition to freezing rain. IFR
conditions are expected with the winter precipitation at the taf
sites. Expect all airports to experience ceilings in the 300 to
700 foot range this afternoon...with these low ceilings expected
to last into Monday. Visibilities will also be up and down as
heavier precipitation moves on and off station.
Warmer air will build into the area tonight...raising surface
temperatures and ending severe clear icing from southwest to
northeast. Subfreezing air will linger longest at lyh...which may
not see freezing precipitation end until 09/12z to 09/14z.
Medium to high confidence on ceilings and visibilities. High
confidence in winds during the taf period.
weather will be quite unsettled through the
first part of the week. A cold front will move through on
Monday...bringing improved flying conditions and a short break in
precipitation as high pressure builds in from the west. Rain...in
addition to MVFR/IFR... will return Monday night through Tuesday
morning as an upper trough moves across the region. High pressure
will build in for Wednesday and Thursday with a return to VFR.
Virginia...Winter Storm Warning until 9 am EST Monday for vaz011-013-014-
Winter Storm Warning until midnight EST tonight for vaz010-012-
Winter Storm Warning until 4 am EST Monday for vaz032-043-044-
Freezing Rain Advisory until midnight EST tonight for vaz007-
NC...Winter Storm Warning until midnight EST tonight for ncz001-002-
Winter Storm Warning until 4 am EST Monday for ncz003>006-019-
WV...Winter Storm Warning until 9 am EST Monday for wvz043>045.
Winter Storm Warning until midnight EST tonight for wvz042.
near term...air mass
short term...air mass