Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1243 am EST Sat Mar 8 2014
high pressure will build into the area overnight into Saturday. A
weaker clipper system will bring some light precipitation to
southeast West Virginia Saturday night into Sunday. Mild high
pressure will control our weather pattern until Wednesday...at
which time...our next weather system is expected to impact the
Near term /through today/...
as of 1115 PM EST Friday...
Areas of fog developing across our southeast counties...especially
the NC counties...where ground is moist from early snow/sleet/ice
and winds calm/clearing skies under high pressure. With some
snow/sleet remaining in these areas...and good radiational cooling
occurring...fog is developing. BUFKIT soundings show good
possibility for dense fog in many of these areas overnight. With
temperatures below freezing...this will be freezing fog depositing
a rime ice on exposed surfaces. Black ice is also an additional
problem. Thus...both have been folded into one product...namely a
freezing fog advisory. Add patchy fog further north...but fog is
not expected to be dense enough west of the Blue Ridge to result
in any significant problems and precipitation was minimal with
little runoff/slush remaining...if any.
As of 300 PM EST Friday...
Rain continues to decrease in coverage and intensity across the
southeast part of the forecast area. Drier air is arriving from the
northwest as the responsible upper low makes progress to the east.
The drier air is also bringing a decrease in cloud
cover...especially over the far western parts of the area where
skies have become mostly sunny with notably warmer temperatures as
compared to the rest of the region.
Through this evening...the above pattern will continue so that the
precipitation will exit/erode in time while cloud cover decreases
from west to east. We expected the last of the rain to end near and
east of South Boston Virginia around 900 PM. Skies will be clear across
the entire area by 300 am.
Winds will also be on the decrease overnight...so that many
areas...especially the Piedmont and mountain valleys...will be calm
or very light. These calm winds...combined with the clear
skies...and a generous region of frozen slop across the southern
half of the forecast area will allow for temperatures to fall below
that which guidance offers. Also...this combination will help set
the stage for fog formation...some of which may be
dense...especially over Southside Virginia and neighboring north
central North Carolina late tonight into early Saturday morning.
On Saturday...zonal flow aloft offering warm air advection...and a
weak downslope component...and more sun than clouds will allow for a
mild day. Will keep the southern half of the area slightly cooler
than guidance because of the wintry ground cover. In general...will
have highs of the low to middle 50s across the mountains and upper 50s
to near 60 across the Piedmont. High level clouds will be on the
increase in the afternoon across the west in advance of an
approaching clipper system.
Short term /tonight through Monday night/...
as of 205 PM EST Friday...
Next passing northern stream trough will push a weak cold front
across the mountains Sat night reaching the Piedmont Sunday morning.
Moisture again looks quite limited with this boundary as it pushes
into low level westerly flow and confluence aloft...with best
chances along the western slopes at this point. Weak Lee trough out
east may allow for isolated rain showers across the NE tier east of the Blue
Ridge per latest NAM but quite iffy. Forecast profiles also suggest
things warm enough for mainly rain with perhaps a few snow showers
across the far northwest mountains espcly if precipitation lingers a bit. Otherwise
running with mostly chance probability of precipitation western third into early Sunday for
low quantitative precipitation forecast and mainly dry elsewhere with increasing clouds overnight.
A drier westerly flow follows the front Sunday afternoon into Monday
night with weak high pressure to the south and troffiness to the
north. Fast flow aloft may bring periodic high/middle clouds through
the period with a little more upslope nature low clouds along the
west slopes later Monday into Monday night with a passing weak
surface trough. Temperatures knocked back a bit Sunday under early clouds
and the 850 mb cool pocket...then finally rebounding to well above
normal levels Monday per downslope...warming aloft and sunshine.
Long term /Tuesday through Friday/...
as of 300 PM EST Friday...
Expecting a Big Warm up ahead of a strong closed low...which will
arrive perhaps next Wednesday. The day before the low and the rain
arrive...some of the warmer spots may cross 70f next Tuesday. Both
the European model (ecmwf) and the ever improving Canadian...indicate a low center
around 995 mb will pass just to the northwest of the region late Tuesday
night or Wednesday afternoon...spreading a swath of stratiform rain
ahead of it...before heavier showers and perhaps a few thunderstorms
develop ahead of a strong cold front on Wednesday. It's definitely
getting closer to Spring when 850 mb temperatures can fall about 10c in a 24hr
timeframe...as values are close to -15c at 850 mb through southeast West Virginia by
12z/7a Thursday. Considering the potential strength of the upper
wave with this very cold air...upslope snows getting underway
Wednesday night may persist into Thursday...potentially with
accumulations across southeast West Virginia. Next Friday morning looks very
cold...with lows potentially in the teens at the coldest locations.
Lack of high latitude blocking allows the anomalously cold airmass
to depart as quick as it arrives...with a more temperate weekend to
Aviation /06z Saturday through Wednesday/...
as of 1243 am EST Saturday...
The combination of clear skies...light winds and snow cover/wet
ground will lead to areas of fog this morning. MVFR/IFR ceiling/visible
are possible in Southside where more precipitation occurred Friday.
Kdan/klyh are the taf sites with the best chance for fog while in
the west...chances are less.
Conditions should quickly evolve into widespread VFR early
Saturday and continue into Saturday evening with only some high
clouds around. Winds may gust to 20 kts with downslope flow
Medium to high confidence in ceilings...visibilities and winds
during the taf period.
Extended aviation discussion...
potential for sub-VFR conditions over southeast West Virginia
Saturday night into Sunday as a clipper and associated cold front
cross the area.
VFR returns behind the front for early next week before another
complex storm system approaches from the west Tuesday night and
Wednesday...bringing the possibility of widespread sub-VFR.
Virginia...freezing fog advisory until 8 am EST this morning for vaz043-
NC...freezing fog advisory until 8 am EST this morning for