Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 271827
Area Forecast Discussion
National Weather Service Blacksburg VA
227 PM EDT Thu Apr 27 2017
Chances of showers and thunderstorms begin this afternoon as a
low pressure system passes to the north. High pressure will
build off the Southeast coast during the next few days to bring
well above normal temperatures.
.NEAR TERM /THROUGH TONIGHT/...
As of 1155 AM EDT Thursday...
A low pressure system centered just north of the Great Lakes is
stretching a cold front southward toward the Ohio River Valley.
An outflow boundary from convection the previous day in this
area should move ahead toward the Appalachian Mountains by the
afternoon. The latest high resolution models show scattered
showers and thunderstorms developing over the Tennessee River
Valley and spreading eastward toward locations west of the Blue
Ridge, but the timing has slowed down by a couple hours and is
reflected in this latest update.
The Storm Prediction Center has the entire CWA outlooked for a
marginal risk of severe thunderstorms today. Model CAPE is
forecast into the 1000-1500 J/kg range this afternoon, but
diurnal gains in buoyancy may be muted by increasing cloud
coverage ahead of the cold front. If sufficient solar heating
occurs, low to mid level flow will encourage momentum transport
capable of supporting locally damaging wind gusts.
Loss of daytime heating will result in a demise of the shower
and thunderstorm activity before midnight. The actual surface
front should dissipate overhead as the building upper ridge of
high pressure acts as a road block to prevent any sort of change
in air mass to the forecast area.
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 400 AM EDT Thursday...
A broad and strong h5 ridge will be centered over the southeastern
U.S. in this period with 588 dm heights over Florida building to
591+ dm just off the Carolina coast by Saturday. This will provide a
very warm and fairly humid air mass across the southern Appalachian
region, especially for late April. High temperatures will run 10 to
15F above normal both Friday and Saturday with highs in the upper
70s to low/mid 80s Friday to mid/high 80s Saturday. Not really
threatening records but still unseasonably warm. Precipitation-wise
do not expect to see much, if any. A strong upper trough will be
digging southward into the southern high plains Friday/Saturday
setting the stage for a heavy rainfall event well to our west,
across parts of the southern and central Mississippi Valley. Forcing
for precipitation in our area will be weak with only a chance for
diurnally driven convection which will be widely scattered and not
hydrologically significant. This will allow the last of our flooded
rivers to continue receding. Models indicate decent ML CAPE of 1-2K
Saturday afternoon but only modest shear but could allow a few
strong to near-severe pulse thunderstorms in the afternoon.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 400 AM EDT Thursday...
Very warm and humid conditions continue Sunday with the chance for
showers and thunderstorms, especially along the Blue Ridge. By
Monday, the vertically stacked upper closed low over the Midwest
will move into the Great Lakes region. This will push a vigorous
cold front into the area from the west with a good chance of showers
and thunderstorms through Monday afternoon into Monday night. High
pressure will then build on for Tuesday with cooler weather and
windy conditions. Moisture increases on Wednesday, with better
chances of rain Wednesday night into Thursday.
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 225 PM EDT Thursday...
VFR conditions should persist for most locations this afternoon,
but there will be scattered showers and thunderstorms that could
limit ceilings and visibilities to MVFR temporarily. An old
outflow boundary ahead of an approaching cold front in the Ohio
River Valley will reach the western Appalachian Mountains, which
should serve as the focal point for any convection. The best
confidence for timing of the showers and thunderstorms comes
between 20Z Thursday to 02Z Friday. Winds will gust out of the
southwest this afternoon due to a 40 knot low level jet.
By tonight, shower and thunderstorm activity should dissipate as
the outflow boundary exits to the east. Model guidance shows
ceilings dropping toward MVFR and possibly even lower at
BLF/LWB/BCB during the night, but confidence was too low at this
time to push it downward as much. Patchy fog will also be
possible at LWB and BCB by early Friday morning, while locations
in the Piedmont should remain VFR. All TAF sites should return
to VFR after 12Z Friday with light south winds expected.
Extended Aviation Discussion...
High pressure should build off the Southeast coast during this
weekend. Other than the potential for MVFR/IFR morning fog at
the usual river valley locations, VFR conditions should prevail
through Saturday. As a low pressure system approaches from the
west on Sunday and Monday, the potential for afternoon showers
and thunderstorms will increase. The cold front associated with
this system should reach the Appalachian Mountains by Monday
afternoon and depart offshore on Tuesday morning, so expect the
best chance of MVFR conditions during the frontal passage.
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