Severe Thunderstorm Warning 132, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
1231 PM EDT Sat Jul 6 2019

.SYNOPSIS...
A persistent weather pattern continues today. On Sunday night
and Monday a wavy cold front will drop south through the Mid
Atlantic region. High pressure builds south down the
Appalachians Tuesday and Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1215 PM EDT Saturday...

Moisture convergence boundary maxed out across the southern
Appalachians at lunch time, with area of storms moving across
the NC High Country into the foothills, with another scattered
area in the Mountain Empire and across the Alleghanys. However,
deep convection mainly limited to the south, but expect storms
to develop or move east out of the mountains this afternoon.
Upper flow out of the wnw should limit coverage east of the Blue
Ridge at times, but still expecting a good coverage on radar
during the afternoon. As has been the case the last couple of
days, not everyone will see rain, but those who do could get a
quick inch or two under heavy storms. Still not seeing enough
organization or signals to warrant a flash flood watch, but
appears the NC mountains are getting more primed in that
direction if more storms move in from TN.

Temps should reach the lower 90s east of the foothills with 80s
elsewhere, with heat indices approaching 100 across portions of
the piedmont.

Previous early morning discussion...

Nightime Microphysics RGB satellite images show fog and stratus
in the valleys of the central Appalachians as mid and high
clouds dissipate and move into eastern Virginia. Will be adding
patchy dense fog in the New and Greenbrier River valleys where
surface observations were reporting visibility of one half mile
or less.

Subtle short wave over the Pennsylvania/West Virginia border
will continue to drift east today with the trough axis into the
eastern half of Virginia by the time of peak heating and
instability. Mean flow changes to west-northwest so coverage of
thunderstorms in the afternoon may not be as extensive as past
couple of days. Enough westerly component to the low level winds
to limit thunderstorms in the foothills of Virginia and North
Carolina.

Will be going with persistence for highs today and lows tonight.
Will also add fog in for overnight in the mountain valleys and where
the probability for thunderstorms is highest during the
afternoon and evening.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 355 AM EDT Saturday...

A southeast-sagging surface trough/cool front, in conjunction with
potentially convectively-induced weak shortwaves aloft from upstream
MCS activity in broader WNW flow aloft, will serve as a focus for
greater thunderstorm coverage into Sunday. This front looks to
trudge into the northern/central Carolinas by late in the day before
stalling near this general area Monday. Little significant change in
air mass behind this surface front, though an easterly wind
component sets up as ridging builds into the northern mid-Atlantic
region Monday. These modest low-level easterlies draw back moisture
westward upslope against the central Appalachians - likely
contributing to widespread clouds and at least showers for Monday,
though thunderstorm chances are lessened by weak instability. Though
still some limited chances for showers across our southern and
southwestern counties, weak subsidence aloft and surface ridging
building into the VA Piedmont may lead to somewhat drier conditions
by Tuesday.

Heavy rain capable of localized areal/flash flooding, and at least
isolated pulse strong thunderstorms capable of localized wind damage
from wet microbursts, should continue to be the main hazards we're
watching for Sunday. Still weak, but somewhat stronger mid-
/upper-level winds may encourage slightly better storm motions but
still carried heavy rain wording in the zone forecast areawide
Sunday. These trends indicated to various extent in available high-
resolution guidance for Sunday, though CAMs notoriously struggle in
weakly-forced large-scale settings like we've been in. Rainfall
intensity/rain-rates should be more gradual and less intense moving
into Monday, though some localized hydro problems could still arise
with upslope-enhanced rain near the Blue Ridge and in areas that
have received antecedent heavy rains.

Should see a SW-NE oriented area of showers/storms Friday progress
slowly southeast along the frontal zone, likely to capitalize on
tall, skinny and weak/moderate CAPE profiles during the mid-
afternoon to mid-evening. Monday has a similar look to something of
a wedge pattern with lots of clouds and widespread rains with
temperatures reduced in these conditions. Any thunder may be more
embedded in more persistent bands and overall coverage of storms
probably no better than isolated given marginal/weak instability. As
rains end Monday night, may have some areas of fog around with wet
ground but didn't place in the grids at this point. For Tuesday,
kept PoPs at Chance levels from Southside to the Blue Ridge
escarpment, then trailing back up along and west of I-77. Greater
instability Tuesday is generally west of our area into eastern
KY/eastern TN. Still carried slight chance PoP for areas northeast
of I-77, but Tuesday on the whole looks dry for these areas.

Still a pretty warm and humid day for Sunday with highs in the 80s
to low 90s. Though there's not much air mass change for Monday
behind the front boundary, it'll be somewhat cooler - in the 70s to
lower 80s with little if any daytime sun - but still on the muggy
side. Temperatures should recover back into the mid 80s in the VA
Piedmont into the southern Shenandoah and Roanoke Valleys, but will
run in the upper 70s to low 80s across the NC foothills/southern
Blue Ridge and along/southwest of I-77.

Forecast confidence is overall moderate.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
As of 300 PM EDT Friday...

Model trends still show some degree of mid level drying behind this
Sunday/Monday wave but no change in low level moisture and still
enough instability for diurnal showers/thunderstorms to develop each
day at least through Thursday and perhaps through Friday as well. It
does look like a stronger upper wave more associated with the
northern stream, vs convectively induced, could sweep across the
Great Lakes and northeast U.S. Thursday into Friday which could add
further to the drying. Will this wave have enough influence to
enhance activity ahead of it and this far south, which is most
likely to be Thursday, and then suppress activity behind it for most
likely next Friday? Or will it have much influence on temperatures?
Hard to say, but model trends in general have been to downplay the
degree of drying and decreased convective coverage during the week
and so for now will keep at least chance PoPs going all next week,
although a little lower for Friday compared to Tues through Thurs.
Temperatures will remain about the same and perhaps just a bit below
seasonal values, with lots of 80s across the region, maybe sneaking
into the low 90s again in parts of the Piedmont by later in the week.

Finally, there are some indications in medium range models of
tropical development in the northern Gulf of Mexico by some time mid
next week along a weak frontal boundary, especially with the ECMWF
model. This will need to be monitored of course, and even though the
previous run of the ECMWF suggested this could eventually get pulled
up the spine of the Appalachians, that scenario currently looks
unlikely given many solutions from other models and their ensemble
members. If there is to be any impact at all in our region it would
be well over a week away, if at all.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
As of 1225 PM EDT Saturday...

Similar to the last two days, will see storms across the
mountains early, then shifting to the foothills/piedmont through
the afternoon. Coverage again will not be organized or high
enough to have predominant thunderstorms in the tafs, but will
have tempo groups at a few taf sites, namely LYH and BLF and
perhaps LWB where radar/meso model trends favor a better chance
of storms here.

Expect VFR outside of the storms, and sub-MVFR potential in
storms.

MVFR to IFR fog and stratus is expected to develop again after
midnight. Locations that have rain in the afternoon and evening
will have a higher probability of getting IFR to LIFR conditions
overnight.

Confidence is above average for thunderstorm chances this
afternoon and evening. Confidence is average for location of
storms today. Confidence is lower on how low cigs/vsbys get
tonight, and when they lift Sunday. Looking at showers/storms
increasing in coverage by end of the taf period, especially
north of a BLF-LYH line.

.Extended Aviation Discussion...

Scattered to numerous showers and thunderstorms are expected
again Sunday afternoon and evening. Storms will be associated
with MVFR/IFR visibilities due to heavy rain, cloud bases
favoring VFR. Aside from the convective threat, some late
night/early morning fog/stratus is possible Sunday night
depending on degree of overnight clearing, especially in
mountain valleys.

Monday through Wednesday remains unsettled with the passage of
a wavy cold front from the north. Pattern is beginning to
resemble a weak wedge with rain and MVFR conditions.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

SYNOPSIS...AMS
NEAR TERM...AMS/WP
SHORT TERM...AL
LONG TERM...SK
AVIATION...AMS/PM/WP

Hazardous Weather Outlook
National Weather Service Blacksburg VA
548 AM EDT Sat Jul 6 2019

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>044-507-508-071000-
Ashe-Alleghany NC-Surry-Stokes-Rockingham-Caswell-Watauga-Wilkes-
Yadkin-Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Grayson-
Carroll-Floyd-Craig-Alleghany VA-Bath-Roanoke-Botetourt-Rockbridge-
Patrick-Franklin-Bedford-Amherst-Henry-Pittsylvania-Campbell-
Appomattox-Buckingham-Halifax-Charlotte-Mercer-Summers-Monroe-
Eastern Greenbrier-Western Greenbrier-
548 AM EDT Sat Jul 6 2019

This Hazardous Weather Outlook is for north central North Carolina,
northwest North Carolina, central Virginia, south central Virginia,
southwest Virginia, west central Virginia and southeast West
Virginia.

.DAY ONE...Today and tonight.

Scattered to numerous thunderstorms will be slow moving. This may
cause localized flash flooding.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Showers and thunderstorms Sunday may produce locally heavy rain that
results in flash flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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