Severe Thunderstorm Warning 174, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
658 PM EDT Wed Jul 31 2019

.SYNOPSIS...
The weather pattern will be quite stagnant across the
Appalachians and central mid Atlantic region for the next
several days. This will allow an old frontal boundary to combine
with upper level disturbances to keep showers and thunderstorms
with heavy rainfall in the forecast through the first part of
the weekend.
&&

.NEAR TERM /THROUGH THURSDAY/...
As of 245 PM EDT Wednesday...

In similar fashion to yesterday, scattered thunderstorms have
developed early this afternoon aided by forcing from the
lingering frontal boundary. Not a lot of dynamic support for
widespread organized convection, but outflow boundary
interaction and moderate instability will help some storms with
strong gusty winds to pulse up from time to time. Very heavy
rainfall is also possible with the stronger storms and some
localized hydro issues are possible.

Expect the storms to continue into this evening with a typical
diurnal trend, though there looks to be enough synoptic support
to help precipitation linger deeper into the evening and
anticipate that some showers will be wafting around through the
overnight. There will also be some fog especially in the valleys
west of the Blue Ridge.

With little change in the overall pattern and another shot of
short wave energy rotating into the upper trof over the eastern
US, expect another round of showers/thunder on Thursday with a
continued localized severe/hydro threat.

Temperatures tonight will be mild with readings in the 60s.
Highs tomorrow will remain near 90 east of the Blue Ridge,
generally lower 80s to the west.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 330 PM EDT Wednesday...

Little significant change to the synoptic pattern through the
period and beyond. A wet and unsettled weather pattern will
continue to be the rule as a nearly stationary and slowly
eastward moving upper-level trough interacts with a plume of
subtropical moisture (PWAT values between 1.5 to 1.8") around
the periphery of the Bermuda ridge. In addition to the Gulf
moisture this will bring northward well into the eastern CONUS,
as well as watching the tropical Atlantic for possible
disturbances tracking near the east coast. These features will
interact to likely yield several opportunities for showers and
thunderstorms that could result in downpours, especially toward
the late week and weekend.

There remain considerable differences between the ECMWF and GFS
in these later periods as to how slow the trough will shift
eastward and flatten. Though guidance is consistent on large-
scale features, they continue to show limited consensus
in timing and magnitude, which will clearly impact the amount of
rainfall. At this point, no well organized event appears, but
the possibility of localized flooding will increase from
repeated days of showers and thunderstorms, obviously affecting
the same locations at times.

It remains difficult, as is typical in convective regimes to
pinpoint down this far in advance where flooding will become the
most significant problem. In addition, flash flood guidance
still is on the high side currently and rivers are currently
near base flow levels. Flash flood guidance values are likely
to lower as rain continues to accumulate, however. The potential
for at least small basin flooding certainly isn't out of the
question moving forward with time. Somewhat greater concerns for
heavy rains could arise by Thursday into Friday in the
Piedmont, Southside and foothills, as the upper-level trough
axis shifts over our area and leads to weakening mid-/upper-
level winds and resulting slower storm motions. With still a
considerable level of uncertainty in QPF and in flood potential,
it remains prudent to include heavy rain wording in the
forecast for Thursday and Friday across the eastern half of the
area to bring awareness to the potential for increased flooding.
This also meshes with messaging in WPC's Day-2 and Day-3
excessive rain outlooks. Will continue to message heavy rain and
possible flooding in the HWO.

Atmospheric soundings will trend toward saturated with time and
not particularly conducive to severe. Abundant cloud cover and
precipitation will also reduce instability by holding
temperatures down somewhat.

Highs will trend somewhat below normal on the highs with less
sun and more clouds/rain, with warmer lows and increased
mugginess. Highs should hover in the low-mid 80s, and lows in
the 60s.

/Confidence in Forecast Parameters/
Temperatures - Moderate to High,
Precipitation Probabilities - Moderate to High
Winds - Moderate to High,
Thunder threat - Moderate to High.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 345 PM EDT Wednesday...

Little to no change in the overall synoptic pattern across the
U.S. is expected during the longer range periods. A massive
hot upper ridge will dominate the western U.S. with general and
broad troughing in the east. A weak frontal boundary separating
true tropical air from semi-tropical air will likely linger
through the weekend and into early next week across the TN
Valley and into the Carolinas. The flow aloft will be northwest
and a series of weak disturbances will likely traverse the flow
and enhance convection from time-to-time. Given the warm, moist,
atmosphere remaining in place across the region, development of
showers and a few thunderstorms will be easy to come by. As the
upper trough axis drifts a bit further east next week, the
coverage of convection should decrease a bit, but remain in the
chance to high chance category as literally no change in the air
mass or overall synoptic pattern is expected.

The main concern going into the weekend and early next week will
be the growing threat for heavy rain and localized flooding.
With tropical moisture or at least semi-tropical moisture in
place and weak steering currents, thunderstorms/showers will be
efficient rain producers and areas that see repeated rainfall
day-after-day or where thunderstorms persist over a short period
of time, could trigger localized flooding.

Little change in temperature is expected during the period as
well with low temperatures in the 60s west to the 70s east with
high temperatures held mainly into the 70s mountains and 80s
Piedmont. Humidity levels will be high, so it will basically
feel pretty muggy.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 655 PM EDT Wednesday...

Scattered thunderstorms linger across the region this evening
with added coverage likely to pop up in spots before complete
loss of heating. However with the upper trough overhead and a
surface cold front to the west, may also see enough forcing to
help showers persist a bit later into the evening. In addition,
expect some isolated showers will be around through the
overnight, especially west of the Blue Ridge. Some storms will
produce heavy rainfall and reduce flight categories to MVFR/IFR
over the next hour or two. To cover the situation will keep use
of VCTS, with a Tempo for sites where appears best coverage may
linger, espcly southeast and across the west. Also expect some
fog overnight especially west of the Blue Ridge with valley
locations trending down to IFR/LIFR, so beefed up coverage.

Convection will fire once again on Thursday with mostly showers
developing by midday, leading to deeper convection for most
areas during the afternoon. Since this appears most likely
across the mountains, included a prevailing group for storms
Blue Ridge west during the afternoon.

Winds near thunderstorms will be variable and gusty through
Thursday. Winds outside of storms will generally be light and
variable with more of an east/southeast component by Thursday
afternoon.

.Extended Aviation Discussion...

A cold front will remain stalled over the area through the end
of the week. Scattered to numerous showers and thunderstorms
with periods of sub-VFR ceilings can be expected through
Sunday or Monday with coverage becoming less by early next week.
This pattern will also result in an increase in MVFR or lower
clouds and MVFR fog due to moist low levels.

&&

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

&&

SYNOPSIS...MBS
NEAR TERM...MBS
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...AMS/JH/MBS

Hazardous Weather Outlook
National Weather Service Blacksburg VA
351 PM EDT Wed Jul 31 2019

NCZ001>006-018>020-VAZ007-009>020-022>024-032>035-043>047-058-059-
WVZ042>044-507-508-011100-
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-
351 PM EDT Wed Jul 31 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...This afternoon and tonight.

Isolated to scattered strong to severe thunderstorms will be possible
this evening until around sunset. Damaging wind gusts and localized
flooding will be the main hazards. Marginally severe hail will also
be possible in the strongest storms.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Scattered to numerous showers and thunderstorms are expected each
day, decreasing slightly during the weekend and early next week. The
main concern will be locally heavy rainfall and repeated rainfall
from day-to-day resulting in localized flooding. A few storms could
also be severe at times.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed at times through the period
primarily to help identify wind damage and areas of flooding.

RAB

Special Weather Statement
National Weather Service BLACKSBURG VA
619 PM EDT Wed Jul 31 2019

NCZ005-006-312245-
Rockingham-Caswell-
619 PM EDT Wed Jul 31 2019

...A STRONG THUNDERSTORM WILL AFFECT EASTERN ROCKINGHAM AND WESTERN
CASWELL COUNTIES...

Until 645 PM EDT.

At 619 PM EDT, a strong thunderstorm was located over Lawsonville,
moving east at 10 mph.

Wind gusts up to 50 mph and dime size hail are possible with this
storm.

Locations impacted include...
Reidsville...
Yanceyville...
Bethel...
Providence...
and Jericho.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 3625 7964 3631 7970 3654 7947 3654 7932
      3625 7933 3625 7953 3624 7953
TIME...MOT...LOC 2219Z 247DEG 10KT 3638 7955

RS

Special Weather Statement
National Weather Service BLACKSBURG VA
625 PM EDT Wed Jul 31 2019

VAZ044-058-312300-
Halifax-Pittsylvania-
625 PM EDT Wed Jul 31 2019

...A CLUSTER OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN
HALIFAX AND NORTHEASTERN PITTSYLVANIA COUNTIES...

Until 700 PM EDT.

At 622 PM EDT, a cluster of strong thunderstorms will move northeast
at 15 mph across the area.

Winds in excess of 40 mph and dime size hail are possible with this
storm.

Locations impacted include...
Chatham...
Gretna...
Mt Airy...
Ingram...
and Nathalie.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 3668 7919 3690 7951 3708 7922 3708 7920
      3705 7919 3707 7918 3700 7890 3698 7890
      3698 7889 3699 7886 3697 7880
TIME...MOT...LOC 2222Z 229DEG 15KT 3682 7928

RS

Special Weather Statement
National Weather Service BLACKSBURG VA
656 PM EDT Wed Jul 31 2019

NCZ006-312330-
Caswell-
656 PM EDT Wed Jul 31 2019

...A STRONG THUNDERSTORM WILL AFFECT CASWELL COUNTY...

Until 730 PM EDT.

At 655 PM EDT, a strong thunderstorm was located near Yanceyville,
moving east at 20 mph.

Winds in excess of 40 mph and pea size hail are possible with this
storm.

Locations impacted include...
Yanceyville...
Bethel...
Providence...
Jericho...
and Prospect Hill.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 3625 7946 3654 7947 3654 7914 3624 7916
TIME...MOT...LOC 2255Z 250DEG 16KT 3636 7940

RS

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