Special Weather Statement, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
209 PM EDT Sun Jul 11 2021

.SYNOPSIS...
Scattered showers and thunderstorms will continue each afternoon
and evening. Ridging builds in from the east tomorrow and will
keep most precipitation and lightning over the western mountains.
The airmass will remain hot and humid overall.

&&

.NEAR TERM /THROUGH MONDAY/...

As of 130 PM EDT Sunday...

The Mid Atlantic region was in between strong ridging over the
western Atlantic and a digging closed low over the Midwest. This put
us in southwesterly flow aloft, with the jet stream and vorticity
maximums to our west. At the surface, the main surface low was back
in IL/IN with a wavy warm front extending through Ohio and the
Virginias. A cold front was over the southern Plains, making for a
broad warm sector.

We are on the eastern envelope of the stronger storms today, but we
have enough instability (MLCAPEs around 1500-2000 J/kg) and forcing
for ascent so that airmass thunderstorms are giving way to more
organized multicells. These more organized storm structures
will continue to feed off of existing outflow boundaries in the
region from previous or ongoing convection, and form broken
QLCS lines through this evening. Convection overall so far looks
similar to yesterday, and some areas will see more than one
round of rain/storms. Training along with deep warm cloud depths
and PWATs in excess of 1.50" will increase rain efficiency, and
heavy rainfall leading to flash flooding is possible. The added
downward momentum transfer of this mass will support damaging
winds in the strongest storms, especially in bowing segments.

Convection will begin to taper off tonight, similar to last night,
with the loss of heating. The warm frontal boundary will lift north
overnight. Expect another night of widespread fog and stratus late
tonight into the earlier morning hours Monday, in particular over
the river valleys. Overnight lows will be warm again and in the
lower to mid 60s along and west of the Blue Ridge, and in the upper
60s/lower 70s to the east.

On Monday ridging will push in from the southeast, especially
from 7H up. It will be another hot and humid day, with highs at
our slightly above climate norms. The ridge will limit our
thunderstorm activity somewhat west of the Blue Ridge. Still
expecting some showers and thunderstorms to form in the heat of
the day, especially over the mountains, but the severe threat
will be diminished.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...

As of 130 PM EDT Sunday...

During this portion of the forecast, the region will remain between
high pressure off the coast of the Carolinas, and a trough/low
somewhere across the central portions of the country. The question
mark in this pattern remains how much capping influence will the
high/ridge have versus how close in proximity will the upper trough
and surface be to act as a focus for convection initiation. The
answer regarding at least the trough position will be an increasing
favorable position for convection initiation as the feature makes
gradual progress eastward Monday night through Wednesday. The trend
will make showers and storms more probable across the far western
sections of the region, especially during the afternoon and evening
hours. However, but Wednesday night, the trough both washes out and
continues its progression into parts of New England, allowing for
any surface front to also wash our, and/or retreat back to the north
by daybreak Thursday.

Temperatures during this portion of the forecast will average a few
degrees above normal, with Tuesday slightly warmer than Wednesday.

Confidence in the above weather scenario is moderate to high.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...

As of 1145 AM EDT Sunday...

For the first half of this portion of the forecast, while we will
remain within a warm and moist atmosphere, any frontal boundary
north of the region is expected to remain well north of the region.
This will limit the focus for convection to weak orographical
convergence and areas of differential heating, all while
encountering some degree of capping from the western Atlantic high.
The result will be isolated to scattered coverage of showers and
storms that should dissipate quickly at sunset.

As we progress into and through the upcoming weekend, the upper
level low across the Upper Mississippi Valley is expected to open
into a more progressive wave, and head east to along the border of
southern Quebec and Ontario. Its associated cold front is expected
to approach, and possibly reach our area. This feature will bring
lifting mechanism needed (the front and better divergence aloft) to
support better coverage of showers and storms, and slightly cooler
high temperatures. Showers and storms will have a better chance of
continuing past sunset, along with the potential for redevelopment,
especially across western sections of the area, nearest the cold
front.

Temperatures during this portion of the forecast will be within a
couple of degrees plus or minus of normal conditions for this time
of year. However, high temperatures will trend slightly cooler
through the period while low temperatures may inch upward slightly.

Confidence in the above weather scenario is moderate to high.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...

As of 200 PM EDT Sunday...

Showers and thunderstorms have developed and have already
affected a number of TAF sites, and expect widespread TSRA
through the evening. This will mean MVFR ceilings/visibilities
or perhaps lower if right under a thunderstorm with heavy rain.
The mean wind forecast is from 215 at 15 kts, so expect general
thunderstorm cell movement from the southwest to northeast this
afternoon. Away from any thunderstorm activity, expect VFR.

-TSRA diminished overnight, but low level moisture remains and
 there will be more fog and low stratus which will improve
 after 12-13Z Monday. Additional -TSRA is expected tomorrow but
 will mainly affect LWB and BLF with ridging building in over
 the east.

Extended Aviation Discussion...

Daily afternoon and evening showers and thunderstorms look to
continue for the Monday through Friday timeframe. Thunderstorm
activity will mainly be confined to the mountains Monday through
Wednesday as ridging and subsidence aloft starts to build from
the southeast. Better chances for storms arrive Thursday and
Friday as our next front nears the area.

&&

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

&&

SYNOPSIS...SH
NEAR TERM...SH
SHORT TERM...DS
LONG TERM...DS
AVIATION...SH

Hazardous Weather Outlook
National Weather Service Blacksburg VA
215 PM EDT Sun Jul 11 2021

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>044-507-508-121815-
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-
215 PM EDT Sun Jul 11 2021

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...This afternoon and tonight.

Strong thunderstorms will affect the area through this evening, and
may produce damaging winds and flash flooding due to heavy rainfall.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

There is a low probability for widespread hazardous weather.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

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Special Weather Statement
National Weather Service BLACKSBURG VA
327 PM EDT Sun Jul 11 2021

NCZ001-002-018-VAZ009-012-015-112015-
Ashe-Watauga-Alleghany-Grayson-Wythe-Smyth-
327 PM EDT Sun Jul 11 2021

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT
NORTHWESTERN ALLEGHANY...NORTH CENTRAL WATAUGA AND ASHE COUNTIES IN
NORTHWESTERN NORTH CAROLINA...EASTERN SMYTH...WESTERN WYTHE AND
CENTRAL GRAYSON COUNTIES IN SOUTHWESTERN VIRGINIA...

At 326 PM EDT, radar indicated strong thunderstorms were located
along a line extending from near Marion Wytheville to near Flatridge
to near Lansing. Movement was northeast at 20 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Wytheville...
Jefferson...
Rural Retreat...
West Jefferson...
Lansing...
Mouth Of Wilson...
and Mount Rogers National Recreation Area.

Locally heavy rain will quickly reduce visibility and result in
ponding of water on roadways, standing water in low lying areas, and
minor flooding of creeks, streams, and areas of poor drainage.
Drivers are urged to slow down and use extra caution to avoid
hydroplaning.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 3636 8180 3634 8177 3634 8171 3636 8172
      3639 8173 3640 8174 3643 8172 3646 8172
      3647 8170 3648 8170 3670 8146 3692 8147
      3703 8112 3702 8111 3703 8109 3683 8103
      3627 8145 3634 8184
TIME...MOT...LOC 1926Z 237DEG 18KT 3689 8139 3668 8133 3648 8146

RAB