Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 172330

Area Forecast Discussion
National Weather Service Blacksburg VA
730 PM EDT Thu Oct 17 2019

High Pressure will build across the area tonight, passing overhead
Friday.  This will result in mainly clear skies and diminishing
winds. Another opportunity for rain is expected as early as
Saturday evening as an area of low pressure moves out of the
Gulf of Mexico and passing off the southeast Atlantic Coast. A
cold front will cross the Mid-Atlantic region Monday night into
Tuesday, providing yet another opportunity for rain.


As of 657 PM EDT Thursday...

Forecast on track with winds beginning to more quickly
diminishing now that sun has set, with exception of ridges.
Minimal upslope low clouds on far wrn slopes, mainly NW
Greenbrier County, and not seeing any enhancement to some
patches of clouds coming across WV with a weak upstream wave, so
while it may still take a while for all clouds to dissipate
along the wrn slopes, do not think they will expand much
overnight, and removed even slight chc mention of a sprinkle in
wrn Greenbrier for this evening. Otherwise manly clear skies,
diminishing winds but not becoming calm except for a few
isolated mtn valleys, thus frost should be limited but there
will be some areas where temps get very close to freezing thus
the advisory headlines for much of the mountains.

As of 330 PM EDT Thursday...

High Pressure will build across the area tonight, passing overhead
Friday.  This will result in mainly clear skies and diminishing
winds. Upslope strato-cu is still possible in the mountains of
WV, but in general, expecting clear skies. Temperatures tonight
will flirt with the freezing mark across areas west of the Blue
Ridge, this may result in frost formation for the valley
locations if the winds decouple. Models maintain a steady breeze
across the ridges for most of the night, so not overly
confident the winds will completely go calm enough for a long
enough period of time in the valleys to promote frost. That
said, still chose the path of least regret and issued a frost
advisory to better advertise the near freezing temperatures and
potential for damage to sensitive plants. We are now getting
late enough in the season that most folks look the other way and
let their annuals take the hit. Our cutoff date for issuing
frost/freeze headlines for the mountains is Oct we
are getting pretty close. As for the eastern CWA, we continue to
entertain headlines until Nov 15th or until a widespread freeze
occurs. That said, temperatures for the foothills and piedmont
will dip into the mid-upper 30s some patchy frost
is possible there too.

After a chilly start Friday morning, temperatures are expected
to rebound quickly, responding to what should be a Sunny Day.
With plentiful sunshine, a diurnal temperature range of 25-30F
is likely...afternoon highs ranging from the upper 40s to mid
50s across the highest elevations to the lower 60s in the
mountain valleys, and mid 60s across the piedmont.


As of 300 PM EDT Thursday...

High pressure over the region Saturday morning should allow for
another opportunity for areas of frost, especially in the mountain
and foothill valleys, but the window of opportunity may be narrow as
clouds advancing in advance of what is now potential tropical
cyclone 16 will begin the enter the southern portion of the forecast
area by 12Z Saturday.

There are still some important differences in the model output on
the track of current potential tropical cyclone 16, and a large
spread in the ensembles members on rainfall amounts. With a good
consensus that a period of upslope flow and isentropic lift in
advance of this feature develops Saturday night/early Sunday, feel
precipitation will fall across much of the forecast area as the
ECMWF and NAM show and leaned toward the higher QPF forecasts. With
a wedge of high pressure at the sfc, do not expect winds to impact
our area. Lowered high temperatures Saturday with this wedge in
place along with abundant cloud cover.

Model trends have been to increase the speed of this system, so
trimmed/removed POPs late Sunday and Sunday night, and accelerated
the clearing on Sunday.


As of 300 PM EDT Thursday...

The long-range deterministic models are generally in good agreement
that progressive, yet fairly high amplitude flow, prevails during
this portion of the forecast. There still are some important
differences in the deterministic models with regard to the timing and
amplitude of a shortwave trof that impacts our area Monday night
into Tuesday night with the 06Z GFS faster compared to ECMWF and
Canadian models. Considering the amplitude of the upper air pattern,
favored a slower solution during this period.

In advance of the associated cold front that passes on Tuesday-
Tuesday night, southerly winds 1-2 standard deviations above average
will help transport moisture to bring a widespread wetting rain to
the region. Behind the front, northwest winds 1-2 standard
deviations above average will create gusty winds that may approach
advisory criteria and will require monitoring for later forecasts.

Temperatures will be above normal ahead of the front Monday, with
temps falling below normal behind the boundary Wednesday.


As of 730 PM EDT Thursday...

High pressure will build across the area tonight, passing
overhead Friday. NW winds are beginning to diminish this evening
and will continue to do so the rest of the overnight and will
remain light from the NW all of Friday under mainly clear
skies. One exception would be the ridges west of KLWB where
scattered to at time broken clouds of 1500-2500ft will persist
through late tonight.

Forecast confidence high.

.Extended Aviation Discussion...

VFR conditions are expected regionwide into Saturday, with the
possible exception of some brief early morning valley fog at
KLWB Sat morning, before tropical moisture accelerates toward
the area from a storm that is forecast to move out of the Gulf
of Mexico and across the Southeast states. This will likely
result in sub-VFR weather Sat night into Sunday...especially for
areas south and east of Roanoke, VA. Increasing northeast winds
are likely as well for locations southeast of Roanoke.

A physical break in the rain is expected Sunday night into
Monday before the arrival of a cold front which will likely be
associated with more rain and sub-VFR Monday night into Tuesday.


VA...Frost Advisory from midnight tonight to 9 AM EDT Friday for
NC...Frost Advisory from midnight tonight to 9 AM EDT Friday for
WV...Frost Advisory from midnight tonight to 9 AM EDT Friday for


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