Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
436 am EST sun Feb 1 2015
low pressure centered near Kansas City this morning will move east
today and tonight and will be centered near Pittsburgh by
daybreak Monday before moving off the New England coast Monday
afternoon. A strong cold front will trail south from the
low...sweeping across the middle Mississippi Valley today...into the
Ohio and Tennessee valleys tonight...crossing the Appalachians
mountains early Monday morning. Widespread precipitation will
accompany this storm system with snow north of Interstate 70 and
rain to the south.
Near term /through tonight/...
as of 400 am EST Sunday...
Clouds continue to thicken across the forecast area...all of which
are the result of the developing storm system over the middle part
of the country. Our radar indicates some light returns...but most
of this is virga...precipitation that dries up before reaching the
ground. Surface dewpoints remain in the teens...indicative of the
dry low level air.
It may take most of the day before the airmass over our forecast
area saturates enough to permit precipitation to reach the
surface. By that time is should be warm enough for anything that
reaches the ground to be rain. Sounding profiles this morning are
certainly cold enough to support a wintry form early in the
day...but the chance of getting anything to the surface is pretty
small. Certainly can't rule out a brief period of light sleet or snow
this morning...but the chance for measurable is less than 20
The cyclone which has evolved over the central part of the country
is fairly large. The center of the low was near Kansas City this
morning with snow falling from Nebraska to Ohio...and rain falling
from Missouri to the western Gulf Coast. This area of low
pressure is expected to strengthen as it moves east
today...producing heavy snow from Chicago to Toledo...and
moderate rains for the middle MS valley. The area of low pressure is
expected to reach western Pennsylvania by daybreak Monday with a
cold front trailing south along The Spine of the Appalachians.
Ahead of the front tonight...strong warm air advection per
southwest winds will draw moisture from the Gulf of Mexico
northward into the Tennessee Valley and middle Atlantic. This will
result in a widespread wetting rain for our area which will
persist until the arrival of the front Monday morning. Rainfall
amounts of a half /0.50/ to three quarters /0.75/ of an inch are
likely with this rain episode.
Temperatures today...pending cloud thickness...should climb into
the 40s...and remain there for tonight per the strong warm air
advection. The only area which may dip back into the 30s before
daybreak would be the far western County Warning Area where the arrival of the
cold front will signal a downward trend of the temperature per
cold air advection behind the front. Temperatures at 3-5kft above
the surface are forecast to warm to +6 degree c across the entire
County Warning Area tonight...so not expecting any precipitation type issues
during the overnight.
Short term /Monday through Wednesday night/...
as of 330 am EST Sunday...
As the low slides by to our north it will swing a strong cold front
through the area Monday morning...bringing an end to widespread
precipitation and kicking off upslope snow showers for the far
western slopes. Snow fall amounts look to be on the light side and
do not currently see a need for any winter weather advisories.
Expect temperatures to be falling all day west of the Blue
Ridge...but temperatures may rise just a tad before the front moves into
the Piedmont so temperatures will not start falling there until late
As the cold air advection becomes established and downward momentum
Transfer increases...northwest winds will start to howl Monday
afternoon. The low level wind field does increase but the mixed
layer will be fairly deep which will prevent gusts from maximizing.
This is similar to several recent events and we may end up needing a
Wind Advisory along and west of the Blue Ridge...but currently
expect winds to remain below 50kts and not reach warning criteria.
The wind will combine with cold temperatures Monday night to bring
wind chill values into the single digits west of the Blue Ridge.
Cold high pressure will bring an end to the upslope snow showers on
Tuesday as it settles over the region and brings US quiet weather
and below normal temperatures. As the high slips by to our east on
Wednesday we will see temperatures rebound nicely and rise to above normal
levels ahead of the next cold front approaching from the west.
Long term /Thursday through Saturday/...
as of 300 am EST Sunday...
Weather forecast models have not changed much 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 /09z 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