Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/26/19
Area Forecast Discussion
National Weather Service Blacksburg VA
1053 PM EST Wed Dec 25 2019
.SYNOPSIS...
High pressure will be over the area through Friday
associated with mild dry weather. The next cold front
with any appreciable threat of rain is not expected to
arrive until the weekend with the best chance for rain
occurring Sunday.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 1050 PM EST Wednesday...
Have lowered minimum temperatures for parts of the New River
Valley and around Tazewell/Burkes Garden based on current
conditions. No other changes needed.
For our forecast area, much of the weather discussion the next
few days is much ado about nothing. High pressure is expected
to remain in firm control with very few if any weather hazards.
The regional soundings pretty much sum up the weather...Dry.
With the exception of the boundary layer, and above 300 MB, the
soundings looked like a desert. Above 300 mb there was enough
moisture to support some thin cirrus and contrails. Within the
boundary layer there was enough moisture to support the patchy
morning fog and valley haze.
With high pressure overhead, strong subsidence will prevent
little air movement thus promoting little or no change in
airmass. If anything low level pollutants such as smoke/smog
will become more prevalent decreasing air quality, but doing
little to change the overall weather condition which features
the dry conditions.
Temperatures during the day will favor readings about 15-20
degrees above normal, with overnight lows above normal along
the ridges, but close to normal in the valleys where the strong
surface based inversion will allow for cold/frosty overnight
minimums. Similar to yesterday, some of the deeper mountain
valleys such as the lower Greenbrier...confluence of the New
River near Hinton...may be harder to mix out due to the strong
inversion, thus fog/stratus more favorable there at night and
delaying any daytime warmup until the lower cloud element
lifts/dissipates late morning or early afternoon.
Bottom line, persistence seems to be the best forecast with
mainly clear skies. The higher level, but thin, cirrus may act
to mitigate some of the wild temperature swing, but still
anticipating a fairly large diurnal/nocturnal temperature
difference with lows in the 30s to highs in the 60s. The higher
ridges which will be near or above the inversion will see less
of a swing with overnight lows about 10 degrees warmer than the
valleys, and comparable to the valleys during the day.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 200 PM EST Wednesday...
An upper level shortwave trough is expected to be heading eastward
through the Upper Mississippi River Valley during the day Thursday.
As we progress from Thursday into the start of Saturday, the
shortwave trough is expected to continue heading eastward, pushing
through the northern extent of the upper ridge. This in turn will
help reposition the center of the surface high farther south to just
off-shore the mid-Atlantic region of the U.S. By Saturday, another
shortwave ridge is expected to develop across the eastern U.S. in
response to a deepening upper low/trough over the Central High
Plains states.
No meaningful precipitation is expected during the first transition
when a shortwave repositions our surface high further south. However,
some very light, isolated precipitation is possible late Friday into
Friday evening along the western slopes. Temperatures are expected
to continue to average some fifteen to twenty degrees above normal.
By Saturday night, we transition from dry to wet. The low/trough in
the center of the country is expected to make headway eastward. As
it does, low level southerly flow off the Gulf of Mexico is expected
to increase in velocity and depth and advect plenty of moisture into
our region. Rain chances gradually increase overnight Saturday into
Sunday morning. The most significant rainfall won`t arrive until
later Sunday, which falls into the extended period of the
forecast.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 PM EST Tuesday...
Deep closed upper low over the upper Midwest on Sunday lifts
northeast toward the Great Lakes and New England and weakens by
Wednesday. Guidance is in a little better agreement now on timing of
cold front which this large scale upper level trough will drag
through the Appalachians from west to east. Front should arrive in
west by early to midday Sunday, and exit the Piedmont by Sunday
evening. 12Z ECMWF and especially Canadian still slower than GFS.
Not a deep tap of Gulf moisture ahead of this front and it moves
through rather quickly with better dynamics/lift mainly to the north
of our region, so not expecting heavy amounts of rainfall Sunday
into Sunday evening. Forecast soundings do not indicate much if any
threat of thunder, so have not included it yet but worth keeping an
eye on between daytime timing of front and dew points surging well
into 50s ahead of it.
Airmass behind front not cold enough to turn any precip to snow
showers with upslope flow until maybe Monday night at earliest, and
moisture will be limited by then. Westerly to northwesterly
flow could continue into Tuesday as upper trough may be slow to lose
its influence on our region. In fact, some solutions, like recent
ECMWF cycles, indicate very brief westerly flow behind front and
quick return to southwest flow as upper low weakens over Great Lakes
and no additional short wave energy riding around south side of
broad upper trough, thus really no threat of any linger upslope wit
that idea.
In fact, this also makes a different in terms of gradient behind
front, with GFS-like solutions suggesting fairly strong west to
northwest winds into Tues morning, while the ECMWF and Canadian
ideas indicate a short-lived gradient behind front quickly weakening
on Monday. Even with GFS solution, still likely not looking at
headline criteria winds behind front, but for now am keeping some
gusts up through Monday night into the 30-40mph range with knowledge
that generally guidance under does this. However, these may need to
be adjusted back down a bit if with time the solutions come around
more consistently with ECMWF and Canadian approach of flatter mid
level flow and weaker surface gradient.
Dry high pressure likely to control the weather Tuesday into
Wednesday next week, but still plenty of differences in terms of
potential return of some overrunning moisture with Gulf tap soon
after that depending on which model one believes. This all dependent
on nature of next closed upper system somewhere over SW US around
this time and strength of the surface high over Mid-Atlantic region.
Think this will be dry enough airmass over all that if there is any
overrunning moisture as early as Wed it will have a hard time
precipitating into this air mass until later in the week if at all.
&&
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
As of 605 PM EST Christmas Day...
High pressure surface and aloft will continue to provide good
weather for aircraft operations through this TAF period. Expect
light winds and VFR conditions under high clouds with potential
for some nocturnal IFR fog/stratus development late tonight,
primarily in the valleys west of the Blue Ridge, including KLWB
and possibly KBCB. Any fog/stratus burns off Thursday morning
with VFR all sites through Thursday afternoon.
Extended Aviation Discussion...
Widespread VFR weather conditions are expected through early
Saturday. An approaching front will bring increasing clouds
and the threat for rain Saturday night and Sunday with sub-VFR
possible for the later half of the weekend.
&&
.CLIMATE...
Below are record maximum and minimum temperatures for Christmas
Day.
We won`t be any where near the record minimum temperatures, but
this gives you an idea of how cold it can be.
Dec 25
Site MaxT Year MinT Year LoMax Year HiMin Year
Bluefield 66 2015 -13 1983 2 1983 58 2015
Danville 74 2015 3 1983 28 1989 61 2015
Lynchburg 72 1982 -4 1983 13 1983 59 2015
Roanoke 68 1982 -4 1983 11 1983 55 2015
Blacksburg 68 1964 -8 1983 13 1983 51 2015
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...PM
NEAR TERM...AMS/PM
SHORT TERM...RR
LONG TERM...SK
AVIATION...MBS/PM
CLIMATE...RAB