Special Weather Statement, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
428 AM EDT Sat Jul 17 2021

.SYNOPSIS...
A cold front approaches the area today with more numerous showers
and thunderstorms. A second front passes through the area Wednesday
and Thursday. The passage of this front will introduce slightly
cooler temperatures, and lower humidity.

&&

.NEAR TERM /THROUGH TONIGHT/...
As 355 AM EDT Saturday...

 Showers and thunderstorms expected today into tonight.

An upper level trough over the East will deepen today into tonight.
A strong shortwave will rotate around the upper trough and move
across the Appalachians this afternoon into tonight. As the trough
sharpens, our region is in an area of upper diffluence this
afternoon. A cold front and a prefrontal trof will travel southeast
today into tonight. Scattered showers and thunderstorms will develop
today with the best chances during the afternoon into this evening.
PWATS increase from an 1.25 inch to nearly two inches so some of the
storms could contain heavy rains. Moderate to strong instability
will develop with heating resulting in the potential for a few
strong to severe thunderstorms. The main threats will be gusty winds
and heavy rains. Deep layer shear does increase a little today with
CAPEs climbing to around 1500 j/KG. The day one convective outlook
place eastern areas in a marginal risk for severe weather. High
temperatures will range from the mid 70s in the mountains to the
lower 90s in the Piedmont.

The cold front will drop southeast into the western slopes of the
Appalachian mountains tonight. Before this happens, strong
prefrontal convection will move east of the Blue Ridge this evening
and may linger tonight especially over the piedmont. The intensity
of this convection and rainfall will decrease around midnight, but
light showers may persist overnight into Sunday morning as a
shortwave trough moves east over the region. Areas of fog will
develop tonight into Sunday morning. Low temperatures overnight will
vary from around 60 degrees in the mountains to near 70 in the
piedmont.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 400 AM EDT Saturday...

A slow moving west-east oriented cold front will sag southward
toward the VA/NC border by afternoon. Broad upper troughing will
remain over the eastern U.S. Scattered showers and isolated
thunderstorms will remain possible in the morning along/near the
frontal boundary. Daytime heating will be confined mainly to
the piedmont and Southside VA by afternoon, which where the
strongest thunderstorms would be expected. Currently SPC only
shows general thunder, but notes in the SWODY2 discussion that
an isolated damaging wind gust cannot be ruled out on a
mesoscale basis. The greater threat for severe and flooding
rainfall continues to be Saturday afternoon, not Sunday.
However, locally heavy rainfall will remain possible Sunday
afternoon, especially across the NW NC mountains and into the NC
piedmont and foothills and as far northeast as Danville and
South Boston.

Cloud cover and precipitation will hold temperatures down to
below normal levels, especially in the west and north Sunday.
Highs will be mostly in the 70s, with even 60s in the mountains.
Lows will be mostly in the 60s. 80s are expected across the
piedmont before the precipitation reaches/develops in those
areas Sunday afternoon.

Monday, the front will sag very slowly southward toward the I-40
corridor. How far south the front moves before stalling and how
quickly that occurs remain big questions for the extended
forecast. Confidence is only moderate with respect to the
frontal boundary moving toward the I-40 corridor by Monday
morning. The GFS continues to be on the fast end of the
spectrum in moving the front south, while the ECMWF remains on
the slow end. Have tapered pops from likely far south to slight
chance far north. Areas along/north of the I-64 corridor could
very well remain totally dry Monday, despite the NBMs high
chance pops in those areas which seem unrealistic per any model.
On the other hand NC counties, and especially the NW NC
mountains will likely see another day of scattered to numerous
showers/thunderstorms. Temperatures will remain below normal
across the entire area, but should recover a bit closer to
normal across the northern areas where there will be more
sunshine and heating. There won't be enough drying of the air
mass for dewpoints to drop below 60, so nights will still be
mild to muggy.

/Confidence Levels in Forecast Parameters/
- Moderate to High Confidence in Temperatures,
- Moderate Confidence in Probabilities of Precipitation,
- High Confidence in Wind Direction and Speed,
- Moderate Confidence in Thunderstorm Potential.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 415 AM EDT Saturday...

Little change expected in the synoptic pattern. Broad upper
troughing will persist across the eastern U.S. with the early
week frontal system stalling across the southeastern U.S., but
remaining close enough to potentially tease the southern parts
of the CWA with deeper moisture and possibly a few
showers/thunderstorms during afternoon heating.

By Wednesday, another frontal system will drop southward from
the Great Lakes into the Mid-Atlantic and Ohio Valley. Moisture
will be more limited with this system than with the early week
frontal system, but given mid-July strong heating, reasonably
abundant moisture, and upper troughing/short wave energy, expect
scattered showers/thunderstorms to develop during this time
frame and drift southward. NBM pops are too low for this
scenario so have raised them at least into the 20-30 percent
range and coordinated with neighboring offices for such. This
front will also linger across NC into TN during the later half
of the week and keep a threat of showers/isolated thunderstorms
in those areas all week, less so further north.

Another frontal system approaches in a similar manner by the
weekend. As the upper troughing cuts off in the south central
U.S. and the general flow across the Mid-Atlantic region becomes
more zonal, warm air and deeper moisture will creep back
northward during the later half of the week allowing
temperatures to warm back well into the 80s with 70s mountains
and muggy overnight lows in the 60s to lower/mid 70s locations
such as ROA. Chances for showers/thunderstorms will also be on
the increase across the entire region by the end of the week.

/Confidence Levels in Forecast Parameters/
- Moderate to High Confidence in Temperatures,
- Low to Moderate Confidence in Probabilities of Precipitation,
- Moderate Confidence in Wind Direction and Speed,
- Moderate Confidence in Thunderstorm Potential.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
As of 137 AM EDT Saturday...

MVFR to IFR fog will develop in the western river valleys this
morning but may be hinder by high cloud cover. KLWB with light
winds and low level moisture has the best chance for LIFR fog
after 08Z/4AM. The morning fog will dissipate by 13Z/9AM on
Saturday.

Numerous Sub-VFR showers and thunderstorms will develop after
noon. The highest probability of precipitation will be across
the mountains. Confidence is high enough to bring showers with
VCTS at ROA/BCB west in the afternoon, with less in the east so
leaving VCTS at LYH/DAN. when it rains expect MVFR to IFR
cigs/vsbys. Winds will be erratic and gusty near thunderstorms
this afternoon into this evening.

Areas of fog and low clouds will develop late tonight into
Sunday morning especially where it rained.

Above average confidence for ceiling, visibility and wind.

Extended Aviation Discussion...

Showers/storms will continue into Sunday with sub- VFR ceilings
and visibilities. By Tuesday the boundary will be south of the
region with cooler and drier weather and a return to widespread
VFR conditions. Scattered MVFR storms are possible Wednesday and
Thursday. Some drier air will arrive for Friday.

&&

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

&&

SYNOPSIS...AMS/KK
NEAR TERM...KK
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...KK/WP

Hazardous Weather Outlook
National Weather Service Blacksburg VA
353 PM EDT Fri Jul 16 2021

NCZ001>006-018>020-172000-
Ashe-Alleghany NC-Surry-Stokes-Rockingham-Caswell-Watauga-Wilkes-
Yadkin-
353 PM EDT Fri Jul 16 2021

This Hazardous Weather Outlook is for north central North Carolina
and northwest North Carolina.

.DAY ONE...This afternoon and tonight.

There is a low probability for widespread hazardous weather.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Numerous showers and thunderstorms are expected Saturday through
Monday. Heavy rainfall leading to localized flash flooding will be
possible.

For the period Tuesday through Thursday, the probability for
widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

VAZ007-009>020-022>024-032-WVZ042>044-507-508-172000-
Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Grayson-Carroll-
Floyd-Craig-Alleghany VA-Bath-Roanoke-Botetourt-Rockbridge-Patrick-
Mercer-Summers-Monroe-Eastern Greenbrier-Western Greenbrier-
353 PM EDT Fri Jul 16 2021

This Hazardous Weather Outlook is for southwest Virginia, west
central Virginia and southeast West Virginia.

.DAY ONE...This afternoon and tonight.

There is a low probability for widespread hazardous weather.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Numerous showers and thunderstorms are expected Saturday and Sunday.
Locally heavy rainfall leading to flash flooding will be possible.

Some of the thunderstorms on Saturday afternoon and evening may be
strong to severe. Damaging wind gusts are the primary threat.

For the period Monday through Thursday, the probability for
widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

VAZ033>035-043>047-058-059-172000-
Franklin-Bedford-Amherst-Henry-Pittsylvania-Campbell-Appomattox-
Buckingham-Halifax-Charlotte-
353 PM EDT Fri Jul 16 2021

This Hazardous Weather Outlook is for central Virginia, south
central Virginia and west central Virginia.

.DAY ONE...This afternoon and tonight.

There is a low probability for widespread hazardous weather.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Numerous showers and thunderstorms are expected Saturday and Sunday.
Heavy rainfall leading to localized flash flooding will be possible,
especially Saturday night and Sunday.

Some of the thunderstorms on Saturday afternoon and evening may be
strong to severe. Damaging wind gusts are the primary threat.

For the period Tuesday through Thursday, the probability for
widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

Special Weather Statement
National Weather Service BLACKSBURG VA
435 AM EDT Sat Jul 17 2021

WVZ043-507-508-170930-
Western Greenbrier-Summers-Eastern Greenbrier-
435 AM EDT Sat Jul 17 2021

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT WESTERN GREENBRIER AND
CENTRAL SUMMERS COUNTIES THROUGH 530 AM EDT...

At 435 AM EDT, radar indicated strong thunderstorms were located
along a line extending from 6 miles northwest of Bingham to Bluestone
State Park. Movement was northeast at 35 mph.

Locations impacted include...
Hinton...
Rainelle...
Rupert...
Quinwood...
Renick...
Sandstone...
and Falling Spring.

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 3826 8043 3822 8036 3811 8036 3804 8024
      3753 8101 3758 8109 3763 8107 3771 8094
      3771 8093 3770 8091 3768 8088 3782 8094
      3787 8075 3795 8081 3799 8077 3804 8083
      3806 8080 3806 8087 3810 8088 3808 8071
TIME...MOT...LOC 0835Z 223DEG 30KT 3813 8087 3761 8097

RAB