Special Weather Statement, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
952 PM EDT Sun Apr 12 2020

.SYNOPSIS...
A strong spring storm system will impact our weather tonight
and Monday producing strong gusty winds, heavy rain, and the
potential for strong to severe thunderstorms. Cooler weather
returns for midweek as a series of weak cold fronts drop
southeast across the area.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 945 PM EDT Sunday...

Rain has now overspread most of the forecast forecast area this
evening. Main line of storms and heaviest rain appears to
arrive a little earlier than originally thought, possibly
knocking on the western forecast area border as early as 2 AM -
3 AM.

Temperatures are still rather cool along and west of the Blue
Ridge, with areas in the lower to mid 50s. Upper 50s to mid 60s
east of the Blue Ridge. Still expecting to see temperatures and
dew points continue to slowly rise overnight with strong warm
southerly flow continues to advect warmer temperatures/moisture
northward. Will also begin to see an increase in non-
thunderstorm winds as the low- level jet begins to strengthen
and the pressure gradient tighten as the low pressure to our
west deepens this evening. Still a big question on how much
instability can build in tonight ahead of the front, if any.
More instability will of course heighten the chance of seeing
severe storms. Regardless of instability, still will see a line
of storms/heavy rain push through the CWA. This is a dynamics
driven system and it will not take a very deep storm to tap into
the very strong low- level jet to mix strong winds down to the
surface.

Forecast as of 300 PM EDT Sunday...

What you see out the window at the moment is the proverbial
calm before the storm. There is lots of dynamic energy coming
together in the Nations mid-section, but for the moment our
forecast area is relatively calm. Clouds are streaming into the
area from the southwest along with an increasing coverage of
showers, but the main crux of the activity is not expected until
the overnight period and into early Monday.

As we transition through the evening. The upper flow is
forecast to back ahead of a strong shortwave trough to our
southwest, this wave moving east out of the Ark-La-Tex region
and phasing with a cold energetic northern stream long wave
trough which is sinking southeast from the northern Plains. The
phasing of these two dynamic upper level features is expected to
result in strong surface cyclogenesis, the surface low starting
at 994 mb over Oklahoma this evening and deepening to a 980 mb
low or possibly lower as it reaches the Ohio Valley and Great
Lakes by daybreak Monday. This rapid pressure drop will sharpen
the surface baroclinic zone with the associated cold front
accelerating east across the lower Ohio and TN valleys, and the
Deep South, then crossing the Mid-Atlantic States Monday
morning. The severe thunderstorm potential from the Storm
Prediction Center paints a grim outlook for the southeast U.S
over the next 24 hours, one which will contain life threatening
damaging winds and tornadoes.

For our forecast area there is a myriad of weather threats to
contend with over the next 24 hours. Starting with rainfall,
there is a high likelihood for at least one inch of rain
areawide, and upwards of 2 to 3 inches of rain along the Blue
Ridge Parkway, with the higher amounts favored along the
southern Blue Ridge from Floyd/Patrick counties of VA into the
NC mountains. It is this area where we have highlighted the
greatest risk for flash flooding.

Upslope flow and PWATs exceeding 1.5 inches which is 2-3 Standard
deviations above normal, lend to heavy rain at times across the
southern Appalachians/Blue Ridge. Model blended QPF showing 3+
inches of rain from NC mountains up the Blue Ridge to almost
Roanoke. Per moderate risk of excessive rainfall and flash
flood guidance running lower in the mountains with slower spring
greenup, this easily justifies a Flash Flood Watch for the NC
mtns/foothills to Floyd/Patrick County, VA. Additional notes
about river flooding concerns are highlighted within the hydro
section of this Area Forecast Discussion.

Moving on to the Wind and Thunderstorm Threat.  A 45-60kt low
level jet works in from the southwest/south this evening
enhancing the upslope across the southern Appalachians, and the
low level jet ramps up even more overnight ahead of the surface
cold front. Forecast soundings suggest there will be limited
mixing of these stronger winds initially, but ridges above 4000
ft could easily feel the affects of the LLJ where gusts could
approach 50 kts. At the same time showers with deeper convection
will also be increasing across the area. These showers will
have the potential to mix down some of this higher momentum air
even into the lower elevations. As such, have issued a wind
advisory for the entire forecast area beginning 02Z/10PM this
evening.

The passage of a line of thunderstorms will likely lead to the
strongest wind gusts late tonight and early Monday. The
thunderstorms associated with this line are expected to have a
high potential to produce severe weather due to the dynamic
nature of the atmosphere. These storms will be embedded within
an environment characterized by 1000-1500 J/kg MLCAPE along with
50+ kt effective bulk shear and large 0-1 km hodographs. This
environment will promote an ongoing risk of embedded supercells
and bowing segments capable of damaging wind and tornadoes. The
severe threat will persist until the passage of the surface
front which is expected to clear roughly a Bluefield WV to Boone
NC line by 12z/8AM, Lewisburg/Blacksburg/Roanoke/Mt Airy
corridor around 13Z/9AM, then east of a Lynchburg-Danville line
around 10AM...give or take an hour on the timing. These storms
are expected to be moving between 50-60kts...so the passage will
occur in rapid fashion. That said, even though the crux of the
activity comes through in the morning, embedded deep convection
overnight may mix down some isolated pockets of strong wind
yielding a need for warnings, and the post frontal winds
immediately following the actual line of severe storms may also
promote gusts capable of damage, and thus the reasoning for the
wind advisory remaining in effect until 20z/4PM.

After the front passes, skies are expected to clear rapidly
yielding mostly sunny skies by mid afternoon. The cold air
behind the front is lagging, so there will be a spike in the
temperature once the clouds depart Monday afternoon with highs
potentially testing 80 degrees across the Piedmont. Temperatures
will eventually succumb to the post frontal cold air advection,
but not until Monday night.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM EDT Sunday...

Weak high pressure should build overhead during Monday night, which
will set up a chilly night across the Mid Atlantic. Tuesday morning
appears quiet, but high pressure should give way to an approaching
cold front by late Tuesday. Rain chances should increase on Tuesday
night, and confidence is increasing that the rain will change to
snow showers in the higher elevations. Some flurries may even spread
across a good portion of areas along and west of the Blue Ridge by
Wednesday morning as temperatures dip close to freezing. However, it
appears that most of the Piedmont will remain with just cold rain.

Any appreciable snowfall accumulations from Tuesday night into
Wednesday morning seem to be confined to the higher elevations
across southeast West Virginia and the Alleghany Highlands of
Virginia. There are a few models that push the accumulating snowfall
further eastward toward the I-81 corridor, but it is too uncertain
at this time due to the moisture moving away from the mountains by
midday. Drier air will arrive by Wednesday evening as high pressure
noses over North Carolina. A weak frontal boundary could cross over
West Virginia by Wednesday night, which may allow a slight chance
of light snow showers for the highest peaks of Greenbrier
County.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 PM EDT Saturday...

This forecast period starts with zonal flow aloft and high pressure
building in at the surface. This keeps the weather dry until later
Friday. By Friday, guidance becomes divergent in agreement, leading
to a more ensemble heavy forecast. A shortwave trough passes through
the area later Friday into Saturday, bringing the opportunity for
rainfall into saturday evening. A brief window of dry weather
arrives Saturday into sunday with the return of high pressure before
another shortwave trough passes the second part of Sunday.

Thanks to mostly zonal flow throughout and no foreseeable
significant systems, temperatures look fairly seasonal with highs
each day in the 50-60s and lows in the 40-50s.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
As of 730 PM EDT Sunday...

Deteriorating flight conditions occurring this evening as rain
and rain showers overspread the forecast area. Ceilings are
lowering to MVFR from south to north and eventually into the
IFR category overnight.

Rain is expected to become heavy at times overnight with an
increasing potential for thunderstorms. Forecast sounding
indicated elevated instability overnight, becoming surface
based by daybreak Monday when a solid line of strong to severe
thunderstorms cross the area associated with a strong cold
front. A 50-65kt LLJ is being forecast by the models, thus
increasing the potential for LLWS until after the frontal
passage. Post frontal, southwest to west winds will also be
quited gusty, continuing into Monday afternoon even though
flight conditions with respect to cloud bases and visibility
will be improving. Models suggest rapid improvement of
cigs/vsbys by Noon Monday.

Forecast confidence moderate to high.

Extended Aviation Discussion...

Turbulent mixing from the wind will gradually diminish Monday
night before ending Tuesday. Clearing, on the other hand, is
expected to be temporary. Lowering cloud bases and potential for
sub-VFR ceilings will spread back into the area from an area of
low pressure that forms along the southeast coast Tuesday-
Wednesday.

Should be VFR Thursday with high pressure arriving from the
TN/OH Valley.

&&

.HYDROLOGY...
As of 330 PM EDT Sunday...

Incoming hydro event looks to be roughly 12-18-hour duration from
around 21Z/5PM this evening through 14Z/10AM Monday, with
heaviest of the rain occuring late tonight and up until the
passage of the cold front Monday morning. Models are generally
consistent in producing 1 to 3 inches of QPF. Highest amounts
look to be focused along the southern and central Blue Ridge.
Question is will this be enough to cause flash flooding and/or
river flooding?

Flash flood guidance in 6 hours shows 2-2.5 inches for flash
flooding and given some heavy rains with higher pwats, plus
convective elements, feel the need for the flash flood watch instead
of a flood watch.

However, this does not mean river flooding is not out of the
question.

Current forecasts for the rivers keeps them below flood stage, with
Alderson along the Greenbrier River coming close to minor flood
stage Monday night.

Looking at Ensemble River forecasts from the GEFS and NAEFS show
potential for minor to moderate flooding along the upper Roanoke/New
and Greenbrier Rivers as well as the upper James. This of course
does not include smaller river/streams and will re-evaluate need to
expand the flash flood watch northward or just have a flood watch
for rivers/streams due the runoff.

Soil moisture running about 40-60 percent above normal across the
mountains, and with less vegetation/greenup, runoff will be
increased, mainly in the mountains. Will have to watch for urban
flooding as well.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until 4 PM EDT Monday for VAZ007-009>020-022>024-
     032>035-043>047-058-059.
     Flash Flood Watch until 9 AM EDT Monday for VAZ015>017-032.
NC...Wind Advisory until 4 PM EDT Monday for NCZ001>006-018>020.
     Flash Flood Watch until 9 AM EDT Monday for NCZ001>003-018-019.
WV...Wind Advisory until 4 PM EDT Monday for WVZ042>044-507-508.

&&

SYNOPSIS...PM
NEAR TERM...BMG/PM
SHORT TERM...PW
LONG TERM...RR
AVIATION...BMG/PM
HYDROLOGY...PM/WP

Hazardous Weather Outlook
National Weather Service Blacksburg VA
236 PM EDT Sun Apr 12 2020

VAZ007-009>014-018>020-022>024-WVZ042>044-507-508-131845-
Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Craig-
Alleghany VA-Bath-Roanoke-Botetourt-Rockbridge-Mercer-Summers-Monroe-
Eastern Greenbrier-Western Greenbrier-
236 PM EDT Sun Apr 12 2020

...WIND ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO 4 PM EDT
MONDAY...

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

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

In addition, severe thunderstorms are possible, which may produce
damaging winds and heavy rain that could lead to localized flooding.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

In addition, severe thunderstorms are possible, which may produce
damaging winds and heavy rain that could lead to localized flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed for tonight into Monday morning.

NCZ001>003-018-019-VAZ015>017-032-131845-
Ashe-Alleghany NC-Surry-Watauga-Wilkes-Grayson-Carroll-Floyd-Patrick-
236 PM EDT Sun Apr 12 2020

...FLASH FLOOD WATCH IN EFFECT FROM 6 PM EDT THIS EVENING THROUGH
MONDAY MORNING...
...WIND ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO 4 PM EDT
MONDAY...

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

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.
   Wind Advisory.

In addition, severe thunderstorms are possible, which may produce
damaging winds.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.
   Wind Advisory.

In addition, severe thunderstorms are possible, which may produce
damaging winds.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed for tonight into Monday morning.

NCZ004>006-020-VAZ033>035-043>047-058-059-131845-
Stokes-Rockingham-Caswell-Yadkin-Franklin-Bedford-Amherst-Henry-
Pittsylvania-Campbell-Appomattox-Buckingham-Halifax-Charlotte-
236 PM EDT Sun Apr 12 2020

...WIND ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO 4 PM EDT
MONDAY...

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

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

In addition, severe thunderstorms are possible, which may produce
large hail, damaging winds, isolated tornadoes, and heavy rain that
could lead to localized flooding.

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

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

In addition, severe thunderstorms are likely, which may produce
large hail, damaging winds, isolated tornadoes, and heavy rain that
could lead to localized flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed for tonight into Monday.

PW

Special Weather Statement
National Weather Service BLACKSBURG VA
1117 PM EDT Sun Apr 12 2020

NCZ003-019-020-130330-
Yadkin-Surry-Wilkes-
1117 PM EDT Sun Apr 12 2020

...A SHOWER WILL AFFECT SOUTHWESTERN SURRY...NORTHEASTERN WILKES AND
NORTHWESTERN YADKIN COUNTIES...

At 1116 PM EDT, a shower was located over Ronda, moving northeast at
50 mph.

Winds in excess of 40 mph and locally heavy rain are possible with
this shower. The shower could intensify to a thunderstorm.

Locations impacted include...
North Wilkesboro...
Elkin...
Wilkesboro...
Fairview...
Jonesville...
Dobson...
and Ronda.

LAT...LON 3615 8118 3646 8091 3638 8064 3607 8094
TIME...MOT...LOC 0316Z 220DEG 44KT 3624 8096

DS

Special Weather Statement
National Weather Service BLACKSBURG VA
1137 PM EDT Sun Apr 12 2020

NCZ003-VAZ032-130345-
Surry-Patrick-
1137 PM EDT Sun Apr 12 2020

...A LINE OF SHOWERS WILL AFFECT CENTRAL SURRY AND SOUTHWESTERN
PATRICK COUNTIES...

At 1135 PM EDT, radar indicated showers were located along a line
extending from Pine Ridge to State Road. Movement was northeast at 70
mph.

Winds in excess of 40 mph and locally heavy rain along Interstate-77
is possible with these showers. The showers may intensify to
thunderstorms.

Locations impacted include...
Mount Airy...
Elkin...
Flat Rock...
Dobson...
Mountain Park...
Bottom...
and Pine Ridge.

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

LAT...LON 3633 8087 3634 8088 3651 8079 3656 8072
      3656 8061 3658 8061 3660 8062 3661 8062
      3665 8055 3664 8054 3666 8050 3642 8063
      3625 8087
TIME...MOT...LOC 0335Z 222DEG 63KT 3650 8070 3630 8085

DS

Special Weather Statement
National Weather Service BLACKSBURG VA
1159 PM EDT Sun Apr 12 2020

NCZ003-VAZ016-017-032-130430-
Surry-Patrick-Floyd-Carroll-
1159 PM EDT Sun Apr 12 2020

...A LINE OF SHOWERS WILL AFFECT CENTRAL SURRY...SOUTH CENTRAL
FLOYD...SOUTHEASTERN CARROLL AND WESTERN PATRICK COUNTIES...

At 1158 PM EDT, radar indicated showers were located along a line
extending from near Laurel Fork to Toast to near Burch. Movement was
northeast at 50 mph.

Winds in excess of 40 mph and rainfall rates of 2 to 4 inches per
hour are possible with these showers. The showers could intensify to
thunderstorms.

Locations impacted include...
Mount Airy...
Elkin...
Fairview...
Flat Rock...
Dobson...
Floyd...
and Ararat.

Do not drive your vehicle through flooded roadways.

LAT...LON 3627 8087 3645 8072 3670 8061 3701 8027
      3677 8033 3644 8053 3624 8087
TIME...MOT...LOC 0358Z 216DEG 44KT 3668 8055 3649 8064 3632 8078

DS

Special Weather Statement
National Weather Service BLACKSBURG VA
1224 AM EDT Mon Apr 13 2020

VAZ017-032-033-043-130500-
Henry-Franklin-Patrick-Floyd-
1224 AM EDT Mon Apr 13 2020

...A LINE OF STRONG SHOWERS AND A FEW THUNDERSTORMS WILL AFFECT
CENTRAL FLOYD...NORTHWESTERN HENRY...PATRICK AND SOUTHWESTERN
FRANKLIN COUNTIES...

At 1223 AM EDT, radar indicated strong showers and a few
thunderstorms located along a line extending from Rocky Knob Summit
to near Meadows Of Dan to near Woodville. Movement was northeast at
45 mph.

Winds in excess of 40 mph and locally heavy rain of 2 to 4 inches
per hour are possible with these storms.

Locations impacted include...
Stuart...
Ferrum...
Woolwine...
Endicott...
Critz...
Mabry Mill...
and Philpott Dam.

Do not drive your vehicle through flooded roadways.

LAT...LON 3655 8046 3665 8040 3683 8042 3705 8003
      3688 7994 3663 8011 3655 8039
TIME...MOT...LOC 0423Z 239DEG 39KT 3682 8037 3669 8034 3653 8045

DS

Special Weather Statement
National Weather Service BLACKSBURG VA
104 AM EDT Mon Apr 13 2020

NCZ004-VAZ032>034-043-130530-
Stokes-Henry-Franklin-Patrick-Bedford-
104 AM EDT Mon Apr 13 2020

...A LINE OF STRONG SHOWERS AND A FEW THUNDERSTORMS WILL AFFECT
CENTRAL STOKES...HENRY...CENTRAL BEDFORD...EASTERN PATRICK AND
FRANKLIN COUNTIES AND THE CITY OF MARTINSVILLE...

At 102 AM EDT, radar indicated strong showers and a few
thunderstorms located along a line extending from near Northwest
Smith Mountain Lake to Philpott Dam to King. Movement was northeast
at 75 mph.

Winds in excess of 40 mph and locally heavy rainfall with rates
around 2 to 4 inches per hour are possible with these storms.

Locations impacted include...
Martinsville...
Bedford...
Rocky Mount...
Danbury...
Ferrum...
Big Island...
and Moneta.

Do not drive your vehicle through flooded roadways.

LAT...LON 3626 8044 3675 8019 3718 7988 3755 7937
      3751 7933 3663 7984 3654 7996 3654 8002
      3649 8003 3626 8035
TIME...MOT...LOC 0502Z 221DEG 66KT 3717 7981 3679 8006 3631 8035

DS

Special Weather Statement
National Weather Service BLACKSBURG VA
111 AM EDT Mon Apr 13 2020

NCZ002-003-019-VAZ015-016-130530-
Surry-Wilkes-Alleghany-Grayson-Carroll-
111 AM EDT Mon Apr 13 2020

...A SHOWER WILL AFFECT EASTERN ALLEGHANY...NORTHWESTERN SURRY AND
NORTH CENTRAL WILKES COUNTIES IN NORTHWESTERN NORTH CAROLINA...SOUTH
CENTRAL CARROLL AND SOUTHEASTERN GRAYSON COUNTIES IN SOUTHWESTERN
VIRGINIA...

At 110 AM EDT, a shower was located over Doughton Park, or near
Sparta, moving northeast at 75 mph.

Winds in excess of 40 mph and rainfall rates around 2 to 4 inches
per hour are possible with this shower. The shower may intensify to
a thunderstorm.

Locations impacted include...
Sparta...
Ennice...
Stone Mountain State Park...
Baywood...
Whitehead...
Abshers...
and Lambsburg.

Do not drive your vehicle through flooded roadways.

LAT...LON 3633 8116 3639 8122 3663 8106 3660 8072
TIME...MOT...LOC 0510Z 219DEG 67KT 3641 8113

DS