Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
724 PM EST Friday Feb 27 2015
cold high pressure will build over the region tonight into
Saturday. Our next weather system will bring a light wintry mix
to the area Sunday into Monday. Temperatures will moderate through
the middle of the week...prior to the passage of a strong cold
front Wednesday into Thursday.
Near term /through Saturday/...
as of 230 PM EST Friday...
High pressure will build from the Great Lakes region to over
Pennsylvania overnight. As it does...a ridge of high pressure will
progress south along the Lee of the Appalachians. Once this is
established...low level flow will switch from light northwesterly
flow....to light southeasterly flow. This will have the impact of
bringing low level moisture back into the region and the formation
of low level cloud cover...especially in areas along and east of the
crest of the Blue Ridge. Moisture looks to be too shallow...and lift
too limited for precipitation. However...the trend will be for
increasing cloud cover through the night...especially after midnight.
Forecast low temperatures range from the single digits over the
mountains to the teens across the Piedmont. These temperatures will
easily help refreezing and water the formed on surfaces today from
snow melt. The most likely areas will be east of the crest of the
Blue Ridge where temperatures reached the upper 30s to lower 40s.
Most areas across the mountains maintain temperatures below freezing
today...but had more sun than clouds which could have prompted some
melting by warming the ground surface above freezing. Only the area
between roughly Richlands and western Greenbrier County probably did
not experience any melting with temperatures in the low to middle
20s and mostly cloudy to cloudy conditions most of the day.
The plan is to issue a Winter Weather Advisory for black ice for our
North Carolina counties east of the mountains. For the Virginia
Piedmont...a Special Weather Statement will be issued that addresses
areas of black ice likely overnight. For the mountains...an Special
Weather Statement for isolated black ice will be issued for all but
the far Western Mountain counties.
On Saturday...the cloud cover that develops tonight is expected to
remain in place through at least the morning hours...and slowly give
way to increasing sun during the afternoon. The influence of the
Arctic high will limit temperatures from getting above freezing
at most locations. Highs in the middle to upper 20s will be common
across the mountains with upper 20s to lower 30s across the
Piedmont. The higher end of this range will be near the Virginia/NC
Short term /Saturday night through Monday/...
as of 330 PM EST Friday...
Broad southwest low level winds between the offshore high and and
approaching cold front on Saturday night through Sunday night.
Models were depicting flow directly off the Gulf on Sunday night.
European model (ecmwf) brings the front through early Monday morning. High pressure
begins to build in behind the front later Monday. Coastal trofing on
Sunday and Sunday night will help maintain The Wedge until the front
comes through late Sunday night into Monday morning. Winds become
gusty behind the front on Monday. Strong cold air advection and
decent pressure rises will result in gusty winds. At this time do
not expect wind gusts to exceed 40 knots.
Increasing cloud cover and warm air advection will limit drop in
temperatures Saturday night. Mav guidance showed rising temperatures
at higher elevations overnight. Cloud cover and wedge will hold back
maximum temperature on Sunday. Went cooler than guidance for both
Saturday night and Sunday. On Sunday night expecting enough mixing
and clouds as well as higher dew points to have only a small drop in
temperatures. Stayed close to mav guidance for overnight lows. Cold
front may be just into far western County Warning Area on Monday
morning. Far western counties may reach low temperature for the
night around 12z/7am. High temperature on Monday will depend on how
fast front moves to the East. Piedmont counties have the potential
to warm up into the 50s before the front comes through. In
contrast...very little rise is likely behind the front in the west.
BUFKIT soundings showed the potential for freezing rain and sleet
until Sunday morning. Hot Springs forecast sounding was slightly
colder and indicated snow though much of Sunday.
Long term /Monday night through Friday/...
as of 315 PM EST Friday...
Will start Monday night off dry as high pressure passes from the
southern Great Lakes to New England...and then builds southward
across the middle Atlantic...hugging the eastern face of the
Appalachians. Chilly northeasterly windflow will keep overnight
lows ranging from the low 20s along the Interstate 64 corridor to
around the freezing mark in northern North Carolina. Warm moist
air will enter from the west overnight as a deep low pressure
system ejects from the central rockies...and rapidly pushes toward
the Great Lakes. The warm moist air overriding sub freezing air at
the surface will make an ideal setup for freezing rain for areas
north of Highway 460...possibly as far south as the North Carolina
state line for a few hours.
Temperatures will warm above freezing areawide by late Tuesday
morning as the warmer southwesterly flow aloft mixes down to the
surface...causing any freezing to change over to liquid. Latest
round of weather forecast models agree that the heaviest rainfall
associated with a warm front lifting west of the Appalachians will
remain outside our area on Tuesday...although scattered showers with
brief periods of heavy rain will still be possible. Tuesday
afternoon highs will range from the middle 50s across the mountain
Empire...to the upper 30s near Interstate 64. Tuesday night lows
will fall into the upper 30s and low 40s most locations.
By Wednesday morning...the low pressure system will be located over
southern Canada...and will drag a strong cold front toward the
appalachian chain. Forecast models vary in the timing of the front's
arrival into our area...with the general consensus leaning toward
the front reaching our southeast West Virginia counties during the
evening. As such...expect Wednesday temperatures to be the warmest
we have seen in weeks...with highs ranging from the low/middle 50s
for the mountains...and the upper 50s to middle 60s for the Piedmont.
Atmospheric moisture across our area ahead of the front will be
significantly above normal for early March...so will be keeping our
eye on the potential for widespread heavy rain for Wednesday
evening/Wednesday night...especially if the cold front becomes
stalled across our area as some models suggest. While we should see
a significant reduction in the snowpack across our area before the
heavy precipitation arrives...expect there will still be areas of
frozen ground due to the prolonged cold weather of recent weeks...
which will cause much of the rain to translate directly into runoff
rather than soak into the ground. Will continue to monitor the
evolution of this system through the weekend for the potential of
flooding Wednesday night.
The cold front will represent the leading edge of yet another Arctic
airmass...which will advance from the Central Plains up the Ohio
River valley on Thursday. Downslope northwesterly flow will lead to
drying conditions and diminishing cloud cover across our area...with
afternoon highs ranging from the 30s west to the 40s east.
Aviation /00z Saturday through Wednesday/...
as of 700 PM EST Friday...
VFR conditions are in place areawide as satellite imagery indicates
mostly clear skies this evening but for a few cumulus left across the
mountains. Wind speeds remain north northwesterly in the 5kt to
10kt range as high pressure continues to nudge east south of the
Overnight...high pressure will continue to push east...crossing
the appalachian chain and expanding southward across the middle
Atlantic to hug the eastern face of the mountains by dawn. This
will result in winds becoming increasingly northeasterly through
the night. Toward sunrise...the northeasterly flow will begin to
draw marine moisture across the Piedmont into the mountains...
resulting in areas of IFR/MVFR ceilings that will linger through
the morning. May see an isolated pocket of freezing drizzle develop
as well...but do not expect enough coverage worthy to make
mention in the tafs.
On Saturday...wind flow will continue to veer southeasterly
across the mountains/easterly across the Piedmont as the center of
high pressure shifts off the New England coast. The layer of
MVFR/IFR ceilings will be thin...so expect it to break up to
scattered in and out low clouds...with ceilings holding longest
along the Blue Ridge. Middle and high clouds will increase through
the day in advance of an approaching cold front.
Precipitation will begin to move into the area late Saturday
night...starting off as snow for most locations but gradually
changing over to sleet or freezing rain as warm air aloft builds
northward along the appalachian chain. Temperatures will warm
above freezing from south to north through the day Sunday...
causing all freezing precipitation to change over to rain. MVFR/
IFR ceilings and reductions in visibility due to precipitation are
expected areawide. A sharp cold front will cross the area Monday
afternoon with northwest winds increasing.
On the heels of the Sunday/Monday system will be yet another
potentially potent system that may impact all or parts of the
region Tuesday into Wednesday.
NC...Winter Weather Advisory until 4 PM EST Saturday for ncz003>006-
short term...air mass