Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1231 PM EST Friday Mar 6 2015
cold high pressure will build east into the region through tonight
bringing dry weather. This high will track south of US Saturday
into Sunday. A front moves across by Sunday night.
Near term /through tonight/...
as of 1025 am EST Friday...
All advisories and special weather statements have expired. Strong
March sun will act to melt snow today...though some icy roads are
still possible over the mountains and north of Highway 460 in
Otherwise...expect mostly sunny skies as high pressure works in
from the northwest. Satellite showing narrow axis of stratocu
working west through Southside Virginia into the NC Piedmont. This cloud
cover should scatter out through early afternoon.
High temperatures still on track for middle to upper 20s southeast WV/alleghanys to
around 40 in the foothills/Piedmont of NC.
Previous valid discussion...
Surface high pressure building into the area today from the Ohio
Valley. This high will remain over the region tonight. 850 mb
temperatures do not begin to rise again until tonight.
At 500 mb...two short waves in the northern stream pass just
north of the forecast area this afternoon and tonight. Winds will
pick up from the west at 850 mb behind these waves late tonight.
Ridges will stay mixed tonight but valleys will still decouple.
Expect a large diurnal spread between minimum and maximum
temperatures due to the dry air mass and a large temperature
spread between valley and ridges tonight.
Short term /Saturday through Monday night/...
as of 400 am EST Friday...
Winds will shift west southwesterly on Saturday as a low pressure
system advances across the western Great Lakes...allowing
temperatures across the middle Atlantic to moderate as colder air
retreats back to the north. Abundant sunshine will help afternoon
highs warm into the 40s across the mountains and the low to middle 50s
east of the Blue Ridge. The upper level trough supporting the low
pressure system over the Great Lakes will clip the Interstate 64
region Saturday night...and may see a few light snow showers in that
area persist into Sunday...although truly colder air will remain
well to the north.
Warming will continue into Sunday for much of the region as upper
level windflow becomes increasingly zonal. Despite increasing
afternoon clouds...highs temperatures will range from the middle/upper
40s over the mountains...to the middle/upper 50s across the Piedmont.
Models are in good agreement of a weak upper level disturbance
passing across the Tennessee mountains Sunday night...bringing light
precipitation to our area mainly south of Highway 460. This system
will pass quickly...with only a few hundredths of an inch of light
precipitation...falling mainly as rain as overnight as lows hover in
the middle and upper 30s.
Clouds will be widespread Monday as yet another system approaches
from the south...this one a stronger low pressure system developing
along the Gulf Coast. Moisture will radiate northward from the low
Monday evening...reaching the North Carolina mountains after
sunset...and overspreading the rest of our area by midnight Tuesday.
Again...with a lack of cold air flow into our area...Monday night
temperatures will be above freezing for most of the region...with
precipitation falling as rain. The likely exception where
temperatures will fall below freezing will be the Interstate 64
corridor and a few pockets elsewhere in the mountains. As such...
expect freezing rain and sleet for these areas.
Long term /Tuesday through Thursday/...
as of 100 PM EST Thursday...
A split flow pattern continues across Continental U.S.. the two streams are
prognosticated to merge across the western Atlantic...a few hundred miles
off the coast of the Middle-Atlantic States. For our region...this will
allow potentially for interaction from both streams. Guidance the
past few days has not been consistent with how much or how little
our area would be impacted...and likewise with the timing of any
potential weather makers. The latest iterations do show a bit more
consistency with each other regarding timing...but not by track. The
GFS...ECMWF...and Canadian solutions offer a solution of a southern
stream system Monday night through Tuesday night. The European model (ecmwf) trends
the system the farthest north...bringing precipitation to the whole
region Monday night and Tuesday. The GFS keeps the system southeast
of our region...with little if any impact. The Canadian solution has
the system clip the southern third or quarter of the forecast area.
Our forecast will continue to favor that of the European model (ecmwf)...but with
toned down precipitation chances. The low level temperature profile
along with expected surface temperatures do not favor a lot of
wintry weather. For the most part....rain will fall with the
system...but there will be a some pockets of snow across the
northern portions of the area Monday night...with pockets of
freezing rain on early Tuesday in the north as low level profile
warms even more.
Tuesday night into Thursday...the jet orientation does not change a
whole lot...and there are weaker signals within the models that
another...and weaker system may brush the southern half of the area
with patchy light rain during this time period.
After only a slight cooling trend on Tuesday...temperatures through
Thursday will trend milder. By Thursday...high temperatures will
range from the middle to upper 50s across the mountains to the lower
60s across the Piedmont.
Aviation /18z Friday through Wednesday/...
as of 1225 PM EST Friday...
VFR conditions to occur through this period with high pressure
sliding in from the north. A few scattered/broken clouds around 2-5kft
cannot be ruled out as 12z NAM trying to form these around Roanoke
this evening. Majority keeps things VFR so not going to push the
cloud cover given dry airmass in place.
Will see continued VFR Saturday into Sunday with high pressure
sinking to the south. A quick moving system on Sunday night may
bring a chance of MVFR ceilings and precipitation to kdan.
Low pressure passing from the Gulf of Mexico to off the Carolinas
may bring sub-VFR conditions later Monday night into Tuesday.