Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
1148 PM EST sun Dec 17 2017
a weak disturbance will cross the region overnight into Monday with
high pressure returning to the region by Tuesday. Another
disturbance will skirt mainly the southern half of the region
Tuesday night into Wednesday. The next strong cold front to impact
our region will cross the area on Saturday.
Near term /through Monday/...
as of 1135 PM EST Sunday...
Should stay fairly cloudy overnight with lower level moisture
trapped below subsidence inversion. Models overall keep it dry
through the night, but model soundings suggest potential for
drizzle or very light at times west of I-77 in WV. Temperatures
will fall just a few degrees with lows mainly in the lower to
mid 30s. Patchy fog also not out of the question in the river
Previous early evening discussion...
Forecast updated to increase pops over the North/East per
radar/observations. High-res models continue to favor the west
through the night for best chance of rain/showers, but overall
should see a weakening trend in coverage. Otherwise, forecast on
Previous discussion from early afternoon...
Patchy light rain, and probably a few pockets of sleet, were
progressing across the region in advance of a disturbance in the
central part of the country. The moisture was doing its best to
reach the surface through a decent dry layer aloft. Enough of a dew
point depression exists that as the column moistens, some
saturation at or below a wet bulb of 32 degrees or colder is
expected for a few parts of the area. The resultant temperature
profile may yield some brief sleet within the mix of the patchy
light rain. Precipitation east of the crest of the Blue Ridge will
even more limited than that across the mountains.
As we head through the overnight hours, the same weather is forecast
during the evening, with perhaps a little snow in the mix over
higher elevations of southeast West Virginia. By midnight, and
lasting into Monday, moisture will be on the decrease, becoming very
shallow, just a little bit above the boundary layer. Any remaining
light precipitation will be very light rain or drizzle across mainly
parts of southeast West Virginia. Despite falling temperatures, lack
of saturation with the dendritic growth zone will be lacking. Any
light precipitation that falls with surface conditions at or below
freezing will be in the form of light freezing rain or freezing
drizzle. This scenario looks probable for perhaps only an hour or
two around daybreak Monday across the highest elevations of western
Greenbrier County, West Virginia. Elsewhere, where the light
precipitation is forecast, temperatures are forecast to remain above
Skies are forecast to remain cloudy across the entire region
overnight. By Monday, enough drier air is expected work its way into
the area to allow for clearing skies east of the crest of the Blue
Ridge where a weak downslope component will help add to the cloud
dissipation. Locations across the mountains will remain mostly
cloudy to cloudy on Monday.
Low temperatures tonight are forecast in the low to mid 30s across
the mountains with mid 30s across the Piedmont. High temperatures
Monday of the upper 40s to the lower 50s are forecast across the
mountains with upper 50s to around 60 across the Piedmont.
Short term /Monday night through Wednesday night/...
as of 110 PM EST Sunday...
Not much of a break on Tuesday between the low level moisture
eroding over the mountains in the morning and the mid and high
clouds spreading in from the southwest in the afternoon ahead of the
next system. With all that cloud cover will be trending toward
cooler guidance in the mountains for maximum temperatures Tuesday.
Clouds and precipitation in North Carolina and southern Virginia
will also limit warm up on Wednesday. Will stay close to cooler
guidance for highs.
Best upper diffluence is on Tuesday night and Wednesday morning in
the right rear quadrant of a 140 knot upper jet. Will be trimming
northern extent of precipitation chances and lean toward the GFS
placement of the best probability of precipitation for Tuesday night
and Wednesday. Partial thicknesses off the European model (ecmwf) and GFS were
showing the potential for mixed winter weather on the northern edge
of any remaining precipitation late Wednesday night and Thursday
morning. But BUFKIT shows precipitation has ended by the time
lower levels get that cold.
Long term /Thursday through Sunday/...
as of 110 PM EST Sunday...
Upper low that entered the Pacific northwest on Wednesday will drop
southeast into New Mexico by Thursday night before tracking through
the Great Lakes on Saturday morning. After that long range models
have significant differences. Wpc favoring the ECMWF and European model (ecmwf)
ensemble which digs the long wave trof over the central United
States and brings the polar northern stream upper low into the
northern Mississippi Valley and western Great Lakes on Sunday and
Surface high pressure crosses Virginia on Thursday, then southwest
winds will increase ahead of the the next cold front. The surface
cold front will pass through the mid Atlantic states on Saturday but
then become parallel to the upper flow on Sunday. Truly colder air
and potential for winter precipitation will not be reaching the
region before Sunday.
Aviation /06z Monday through Friday/...
as of 1140 PM EST Sunday...
Sub-VFR in the mountains will persist through the period, with
blf/lwb at times dropping below 1000ft through 10z. Westerly
flow is going to keep MVFR cigs at blf at least until Monday
evening while lwb may jump above MVFR by the end of the period.
The other taf sites will also have MVFR at times early before
scattering out after dawn.
Through Friday, the bulk of the region will maintain VFR
conditions as a split-flow pattern establishes itself across
conus, with our little part of the world remaining in between
systems. The exception to this rule may be on Wednesday when a
southern stream system may be far enough north to provide
sensible weather to at least the southern half of the region.
Our next cold front may arrive Friday night into Saturday. The
latest model guidance offers increasing, gusty winds both ahead
and in the wake of the front, along with sub-VFR conditions.