Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 280611

Area Forecast Discussion
National Weather Service Blacksburg VA
211 AM EDT Thu Jul 28 2016

A wavy front will be nearly stationary from the Mid Atlantic
region to the mid Mississippi Valley through the end of the week.
Weak impulses tracking along the front will combine with deep
moisture to produce periodic rounds of showers and thunderstorms.


As of 945 PM EDT Wednesday...

Atmosphere has generally been worked over in terms of instability
needed for showers/storms. There may be lingering showers and a
few isolated storms overnight but with significantly reduced
intensity due to loss of daytime heating and reduction in
available CAPE. Today`s rainfall will lead to patchy fog
overnight otherwise the main theme for the overnight will be the
high dewpoints (lower 70s most areas and muggy conditions) and a
continuation of the muggy conditions.

As we head to Thursday, models continue to advertise decent
shortwave moving from the TN Valley into the eastern Ohio Valley.
Better upper support with backing winds suggests that higher
threat of showers and storms occurs over the mountains, though
further east is limited some. Any cloud cover tonight into
Thursday from blow off of upstream convection may inhibit stronger
storms in the west, but should be more sunshine in the east. The
Storm Prediction Center Day 2 has a slight risk of severe storms
in our piedmont counties Thursday and marginal elsewhere.

Looking for highs on Thursday to range from the lower to mid 80s
west to lower to mid 90s east.


As of 330 PM EDT Wednesday...

Overall synoptic pattern shows upper ridge across the western states
with broad trough developing across the MS/OH valley as fairly
strong short-wave helps to amplify the trough. This will spin up
a weak surface low...currently forecast by the consensus of
models to pass just to our northwest Thursday night and Friday
with an axis of very high PWATS and the potential for significant
rainfall mainly to our north and west. QPF ranges from less than
0.25 inches far southeast CWA up to possibly 1.50 inches far
northwest. Recently issued WPC Day 2 (12z Thu-12z Fri) Excessive
Rainfall outlook show an area of slight chance for excessive
rainfall mainly north and west as well. Cannot rule out some hydro
issues in our northern counties with this much rainfall but better
likelihood north of the CWA where some Flood Watches have been or
are likely to be issued. At this point no Flood Watches for our
area but will have to monitor closely for any southward shifts in
the expected area of heaviest rainfall. Partial clearing Friday
into the weekend with little significant change in the overall
pattern. Maintaining diurnal thunderstorm chances in the still
moist and unstable air mass. Temperatures near to slightly above
seasonal normals.


As of 330 PM EDT Wednesday...

The generalized pattern over the CONUS will be slow to change in the
extended period as upper ridge builds over the western states an
broad troughing takes hold across the eastern U.S. Expect several
shortwaves will crest the western ridge and help to amplify the
eastern trough early in the period. Meanwhile a surface frontal
boundary will persist in the vicinity of the mid-Atlantic through
the period oscillating somewhat north and south in response to short-
wave activity and modified by rounds of mainly afternoon/evening convection.
The air mass will remain warm and humid through the period with
daily highs near to slightly above normal and lows above normal
due to the high humidity and considerable cloudiness at times. By
Wednesday indications are that H5 heights will begin to rise again
with somewhat drier and hotter conditions for mid-week period.


As of 200 AM EDT Thursday...

Area of showers and thunderstorms with MVFR ceilings and
visibilities over eastern Kentucky and southwest Virginia will
continue to move northeast this morning. Along the Blue Ridge and
into the piedmont of Virginia and North Carolina areas of fog and
stratus will develop. Observations showed high surface dew points
with little to no dew point depression. High confidence of IFR to
LIFR fog at KBCB and KLWB this morning. Medium confidence how far
visibilities will drop at KBLF and KROA. The fog will dissipate
after sunrise with VFR visibility by 14Z/10AM. May take longer for
ceilings to lift back to VFR.

Storms will develop over the mountains during the early afternoon
and then move east into the foothills and piedmont during the mid-
late afternoon. There is a high likelihood for VCTS for all of
the flight terminals in the central Appalachians this afternoon
but timing of MVFR conditions too uncertain to include in the bodyof
the TAFs at this time. Bufkit showed a favorable shear profile
for more organized storms and the potential for microburst winds
within the thunderstorm cores leading to isolated surface gusts of

Coverage of thunderstorms will diminish after sunset in the
piedmont. Scattered showers will continue in the mountains
overnight. Models suggested ceilings will lower to MVFR with deep
westerly winds around 06Z. Have not lowered the ceilings in the
TAFS at this point.

Extended aviation discussion...

An upper ridge of high pressure will remain just south of the
area and a residual frontal boundary will remain over the area through
Monday. This will allow for periodic, mainly diurnally
driven, deep convection. A more widespread sub-VFR potential
exists into Friday per a strong wave of low pressure which will
ripple east along a stalled front. After the passage of this
wave, some decrease in coverage of precipiation is expected over
the weekend. In addition to the thunderstorm threat, late night
and early morning fog will likely occur at the usual valley




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