Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Blacksburg Virginia
940 am EST Tuesday Jan 27 2015
a couple of upper disturbances will affect our weather through
tonight with colder temperatures and gusty winds...along with some
mountain snow showers. High pressure builds in
Wednesday...followed by a clipper for Thursday.
Near term /through tonight/...
as of 935 am EST Tuesday...
Quick update to drop the Winter Weather Advisory across the SW
where basically only seeing flurries and not expecting to see much
added accumulation this afternoon. Also lowered probability of precipitation and adjusted
clouds a bit across much of the west.
As of 700 am EST Tuesday...
Clearing has taken place over the central portions of the forecast
area. Band of light snow has moved east toward I-85-I-95 in Virginia.
Upstream shortwave now over the Cumberland Plateau is aiming to
send most of the snowfall to the smokys this morning...sneaking up
into the NC high country. Accumulations of 1 to 2 inches still
look reasonable across the Tennessee/NC border mountains no major changes to
the previous forecast were made...except adjusting sky cover down
narrow axis of precipitation moving across Southside Virginia early this
morning with some snow...but temperatures running in the middle 30s will
only result in a dusting at most on grassy surfaces.
Upstream...next shortwave diving into Kentucky will slide southeast to
the southern Appalachians by midday. This will bring a shot of snow
showers over the NC mountains northward into southeast WV. Overall...amounts will be
less than 2 inches...but will keep the current advisory for the NC
mountains into Grayson going.
This wave will exit this afternoon with most areas clearing outside
the western slopes. The final piece of energy on the back side of the
upper low across the northeast shifts across the area this evening.
This wave will bring another round of snow showers mainly to the
upslope zones of southeast WV as the main track of the vorticity is further
north. An inch or two could fall with this but not advisory levels.
In addition...models showing good pressure rises with subsidence
with this wave...though surface pressure gradient orientation and 800 mb
winds not favoring a high wind event. Still could see a few hours
this evening with gusts along the Blue Ridge and adjacent areas
reach 40 to 45 miles per hour. Will highlight in the severe weather potential statement.
Will be much colder today in the mountains...thanks to the surge of
Arctic air heading in with gusty winds. Looking at highs in the 20s
over the higher elevations and into southeast WV...to around 30 New River
valley...upper 30s Roanoke...and middle 40s Southside Virginia/northwest NC Piedmont.
Tonight...with winds staying up...should keep enough mixing to
prevent temperatures from dropping really far. Still looking at teens west
to lower 20s east...about 5 to 10 degrees below normal for this time
Short term /Wednesday through Thursday night/...
as of 230 am EST Tuesday...
1029 mb surface high will build east across our region Wednesday.
Low level winds will weaken and become more northerly...thus
ending upslope snow flurries. High temperatures Wednesday will warm
into the upper 20s in the northwest mountains to the middle 40s in the
Wednesday night into Thursday...the surface high center will shift
east of our area...while our next clipper system heads southeast
through the Great Lakes region. Winds will back and increase in
speed. Cloud cover will start to increase from west to east
Wednesday night. Low temperatures Wednesday night are a challenge
with warm advection. Followed superblend for lows with readings from
middle teens in the northwest valleys to middle and upper 20s along the
southern Blue Ridge. A slower arrival of clouds Wednesday night
could allow for cooler valley minimums.
By Thursday morning...the low center is in the Ohio Valley with
trailing cold front southward into western Kentucky. Moisture
arrives early enough in the far west to allow for light probability of precipitation for
snow...before better probability of precipitation to arrive midday into Thursday afternoon.
A rain/snow mix in the west will transition to rain Thursday
afternoon. High temperatures Thursday will vary from the middle 30s in
the northwest mountains to the middle 40s in the Piedmont.
A cold front will move east across our region Thursday evening into
Thursday night. In its wake..upslope snow showers and snow flurries
expected for the western slopes of the Appalachians with blustery
northwest winds. Snow accumulations in the west of an inch or two
may be possible in the western upslope favored locations. Low
temperatures Thursday night will range from around 20 degrees in the
northwest mountains to the lower 30s in the southeast.
Long term /Friday through Monday/...
as of 300 am EST Tuesday...
Below normal temperatures trending to much below through the
extended...along with strong northwest winds Friday and again Sunday
night and Monday.
Upper levels will be evolving to more of a dominant northern stream.
The latest indications point to a colder more amplified eastern trough
developing as per the European model (ecmwf)...and split flow out west with a ridge
for the Pacific northwest and a cutoff low regenerating over the Baja California
The snow showers and blustery conditions will continue Friday. 1036
mb surface high pressure will build east across the region Friday night.
High pressure will remain in control of our weather for Saturday
into Saturday night.
Low pressure will lift north west of the mountains and trailing cold
front will push east Sunday. Moisture ahead and along this frontal
boundary will bring a good chance of precipitation to the region.
The front will push through Sunday night...allowing very strong
northwest winds to usher in a shot of Arctic air and cold
temperatures for the start of next week. The European model (ecmwf) has been
consistent with this message and naefs anomalies now support the GFS
trend toward this solution so confidence is growing in this cold
Aviation /15z Tuesday through Saturday/...
as of 700 am EST Tuesday...
Terminals this period will stay VFR...except at blf/lwb where a
period of MVFR will occur this morning...then again tonight with
next upper disturbance moving across. Winds will be gusty in the
roa/bcb/blf taf...with stronger gusts expect this evening as final
shortwave moves across. Some gusts to 35 kts not out of the
question at airports like hlx-gev.
high pressure on Wednesday will provide a quiet day with VFR
conditions across all taf locations. Another clipper system
arrives on Thursday...bringing a chance of sub-VFR ceilings and
visibilities...with a chance for -shra...-shsn in the mountains.
Another area of high pressure shifts east into the area Saturday
and off the coast Sunday...returning US to VFR.