Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 282058 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Blacksburg VA
358 PM EST Mon Nov 28 2016
A series of weather systems will bring warm and breezy conditions to
the region, along with periods of widespread rainfall, for the next 2
days. Rain will develop ahead of a cold front tonight through early
Tuesday, followed by a low pressure system moving out of the lower
Mississippi valley with more rainfall on Wednesday. Cooler high
pressure will then build in with dry weather expected for the end of
the work week and into the weekend.
.NEAR TERM /THROUGH TUESDAY/...
As of 330 PM EST Monday...
Satellite imagery continues to show thickening clouds over the region,
and returns on radar have yet to reach the ground. But its only a
matter of time before we saturate and get some decent precipitation
going ahead of the front approaching from the west. Believe orographic
effects will generate showers along the Blue Ridge ahead of the main
body of showers with the front, but much of the region will wait until
later tonight for the onset of precipitation. It looks like a solid
shot for precipitation west of the Ridge, but guidance varies a bit on
the integrity of the precipitation shield to the east and will go with
the trend shown in the meso models and taper shower activity off during
the afternoon. Not overly impressed with convective potential as
mid/upper lapse rates are modest and any CAPE is of the long/skinny
variety. While an embedded rumble of thunder is possible, will leave
this out of the forecast for now. Rainfall amounts of 1 to 1.5 inches
can be expected with this shot of precipitation along the southern Blue
Ridge through Tuesday, but amounts up to one half inch will be more
The big concern through tomorrow will be the very strong low level
southerly jet ahead of the front. While the core of strongest winds
will slide by to our west, we will still be within the broad energized
wind field and some very string gusts are expected. This being a warm
advection scenario gusts will have trouble reaching the surface, and
once precipitation begins and lapse rates become less steep downward
momentum transfer will be limited. Will continue the current wind
advisory form the northwest mountains of NC up through the Mountain
Empire of VA as this is a favored area for high winds in this type of
regime, but other locations from the Blue Ridge westward will also be
quite windy through tonight above roughly 3500 feet MSL. As the
strongest winds pull away late tonight, the high wind threat will
diminish by daybreak Tuesday.
Temperatures look to be rising overnight so expect an early low in the
mid 40s to lower 50s, with temperatures by daybreak Tuesday about 5 to
10 degrees warmer. Highs Tuesday will then generally be in the
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 330 PM EST Monday...
Initial round of precipitation will be winding down late Tuesday
with front over eastern VA. Still looking for a 2nd wave of
precipitation to develop in response to strong shortwave rounding
the base of upper midwest closed low. Have kept high chance pops in
overnight but increasing to likely by Wednesday morning. Heaviest
rainfall appears to be during the day Wednesday with WPC and various
model blends suggesting a range between 0.75 to 1.50 inches across
the CWA. No issues expected with p-type as warm advection pushes h85
temps into +10 to +12C and none with hydrology as these amounts will
be insufficient to overcome the incredibly dry antecedent conditions.
Precip event winds down into Thursday with cooler and drier air
working in behind the front. Expect a wide range in high temps
during the day with 40F to 60F SE. Could be brief changeover to snow
in the favored upslope areas but not impressive at all in terms of
wind, cold advection and pressure rises for this activity. H85 temps
only fall off into upper 20s in far NW to mid-30s SE.
.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 330 PM EST Monday...
Friday looks dry and seasonable with highs low 40s NW to low 50s SE
and a Saturday possibly a transition day toward wetter conditions
late weekend. Highs near climo for early December. Still
considerable divergence persisting in the model solutions for the
latter part of the extended. 00Z/28 Euro came in quite wet for
weekend with a deep trough located over Texas and the Gulf opening up
with strong moisture return along with favorable dynamics. Latest
12z/28 operational EC run maintains similar solution with this
fairly bullish scenario for additional precipitation. This in
distinct contrast to last few GFS/CMC runs which keep western trough
much further west, back across AZ or northern Mexico with a flat
zonal flow across the east and little to no northward moisture
return through Sunday. Latest PMDEPD discussion is favoring the run-
to-run consistency of the GFS and maintaining high pressure over our
area through Sunday and suppressing significant precipitation well
to the southwest. Have raised PoPs into chance range starting early
Sunday but confidence is not particularly high.
.AVIATION /21Z MONDAY THROUGH SATURDAY/...
As of 1225 PM EST Monday...
Expect VFR tafs early in the period with a rapid trend to MVFR/IFR
conditions tonight as a front approaches from the west. Expect
precipitation with lower cigs to spread in from west to east, but
some showers will develop in upslope southeast flow along the
southern Blue Ridge ahead of the main precipitation. However, a
bigger concern is the low level jet ahead of the front with a core
in excess of 70kts. The main thrust of the jet will brush our area
as it ride up to our east, but the overall wind field is broad and
there will be a sharp increase in low level winds overnight. Will
include a mention of wind shear due to speed at KBLF and KLWB
since they are closest to the core of highest winds, but a
significant increase in low level wind speed can be expected at
sites through tonight. Believe once precipitation sets in and
lapse rates become less steep this will act to limit downward
momentum transfer so will indicate higher winds before onset of
precipitation. This will have to be monitored closely since a
slower arrival of precipitation will create a larger window for
higher winds to mix down, and any discreet convective elements may
also be more efficient in mixing winds down.
With a lot of flow parallel to the front, it will be in no hurry
to clear the region and may well end up stalling out in our
vicinity. This will allow poor flight conditions to linger through
the end of the TAF period, though winds will be lessening as the
core of stringer winds aloft pulls off to the north.
Extended aviation discussion...
Initial wave of rainfall will exit late Tuesday with leftover
sub-VFR conditions in place before a more significant batch of
rain arrives later Tuesday night and continues into Wednesday
evening. This likely to keep widespread sub-VFR ceilings and
visibilities in place until a cold front passes through the region
early Thursday. Drier air behind the front should result in a
return to VFR east of the mountains while upslope sub-VFR cigs
likely linger across the southeast West Va locations, where rain
or snow showers appear possible. Broad northwest flow looks to
keep this scenario in place on Friday as well with upslope driven
sub-VFR cigs western mountains and mainly VFR to the east.
-- Changed Discussion --As of 330 PM EST Monday...
Wind gusts at the higher elevations will be increasing and become
very strong with values approaching 50 mph especially at locations
above 3500 ft. At lower elevations, gusts on the order of 20 to 25
mph will be more common. Areas east of the crest of the Blue Ridge
will experience minimal gusts. Wind gusts are expected to diminish
with the onset of precipitation as lapse rates become less steep
and limit downward momentum transfer.
Relative humidity values will be steadily increasing and be well above
50 percent by this evening, and remain well above 50 percent through
A series of weather systems will bring widespread wetting rainfall to
the region during the next 2 days. Rain will develop ahead of a cold
front tonight through early Tuesday, followed by a low pressure system
moving out of the lower Mississippi valley with more rainfall on
Wednesday. Total rainfall through midweek is expected to be in the 2 to
3 inch range along the southern Blue Ridge into the mountains of North
Carolina, but amounts of 1 to 1.5 inches will me more common elsewhere.
-- End Changed Discussion --
VA...Wind Advisory until 7 AM EST Tuesday for VAZ007-009-015.
NC...Wind Advisory until 7 AM EST Tuesday for NCZ001-018.
WV...Wind Advisory until 7 AM EST Tuesday for WVZ042.