Alert archive / Virginia / Flash Flood Watches in 2020

Flash Flood Watch 9, NWS Blacksburg, VA

August 12, 20206 counties in Virginia

NWS Blacksburg, VA issued this flash flood watch at Aug 12, 2020, 4:07 AM EDT for 6 counties in Virginia. It took effect at Aug 12, 2020, 12:00 PM EDT. It was in force for 11 hr.

The area

The counties it named.

The facts

Issued: Aug 12, 2020, 4:07 AM EDT (08:07 UTC)
In effect from: Aug 12, 2020, 12:00 PM EDT
Expired: Aug 12, 2020, 10:42 PM EDT
In force: 11 hr
Issued by: NWS Blacksburg, VA
Flood severity: None

Counties Amherst County, VA, Appomattox County, VA, Buckingham County, VA, City of Buena Vista, VA, City of Lexington, VA, Rockbridge County, VA

The radar

The Roanoke radar (KFCX), 123 km from the middle of the area, began a volume at 08:08 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 8.1 hours before the alert went out and 209 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1124 J/kg
Mixed-layer CIN: -15 J/kg
Mixed-layer LCL: 1414 m above ground
0-6 km bulk shear: 14 kt
0-1 km storm-relative helicity: 24 m²/s²
0-3 km storm-relative helicity: 88 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this flash flood watch went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Blacksburg, VA wrote its last area forecast discussion before this flash flood watch went out at Aug 12, 1:26 AM EDT, 2 hours 41 minutes earlier.

Area forecast discussion, Aug 12, 1:26 AM EDT, 2 hours 41 minutes before

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Hazardous weather outlook, Aug 11, 6:26 PM EDT, 9 hours 41 minutes before

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In the hours before

Special weather statement, Aug 12, 2:10 AM EDT, 1 hour 57 minutes before

Special Weather Statement
National Weather Service BLACKSBURG VA
210 AM EDT Wed Aug 12 2020

VAZ035-046-120645-
Amherst-Appomattox-
210 AM EDT Wed Aug 12 2020

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN APPOMATTOX AND
SOUTHEASTERN AMHERST COUNTIES...

At 210 AM EDT, a strong thunderstorm was located over Stonewall, or
near Concord, moving northeast at 10 mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
Bent Creek...
Riverville...
Stonewall...
Oakville...
Spout Spring...
Tower Hill...
and Madison Heights.

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

LAT...LON 3732 7891 3736 7898 3743 7902 3743 7904
      3742 7904 3742 7907 3743 7909 3764 7895
      3754 7890 3755 7888 3754 7883 3755 7882
      3746 7871
TIME...MOT...LOC 0610Z 217DEG 8KT 3744 7895

BMG

The office that day

Everything else NWS Blacksburg, VA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 11, 8:07 PM EDT	Areal Flood Advisory	RNK	Grayson	96 min
Aug 11, 8:22 PM EDT	Special Weather Statement	RNK	Rockbridge, City of Lexington	38 min
Aug 12, 2:10 AM EDT	Special Weather Statement	RNK	Appomattox	35 min
Aug 12, 2:14 AM EDT	Areal Flood Advisory	RNK	Tazewell	92 min
Aug 12, 2:42 AM EDT	Areal Flood Advisory	RNK	Amherst, Appomattox, Campbell	3 hr
Aug 12, 3:16 AM EDT	Areal Flood Advisory	RNK	Buckingham	119 min
Aug 12, 12:58 PM EDT	Areal Flood Advisory	RNK	Grayson	104 min
Aug 12, 2:25 PM EDT	Areal Flood Advisory	RNK	Carroll, Patrick	3 hr
Aug 12, 2:37 PM EDT	Areal Flood Advisory	RNK	Tazewell	3 hr
Aug 12, 3:11 PM EDT	Areal Flood Advisory	RNK	Giles	3 hr
Aug 12, 3:15 PM EDT	Areal Flood Advisory	RNK	Smyth, Tazewell	3 hr
Aug 12, 3:46 PM EDT	Flash Flood Warning	RNK	Tazewell	4 hr
Aug 12, 4:04 PM EDT	Special Weather Statement	RNK	Franklin, Henry, City of Martinsville	56 min
Aug 12, 4:38 PM EDT	Areal Flood Advisory	RNK	Franklin, Henry, Patrick	3 hr
Aug 12, 6:42 PM EDT	Areal Flood Advisory	RNK	Amherst, Rockbridge, City of Buena Vista, City of Lexington	3 hr
Aug 12, 7:19 PM EDT	Flash Flood Warning	RNK	Rockbridge	3 hr
Aug 12, 3:19 PM EDT	Areal Flood Advisory	RNK	Alleghany, Surry, Wilkes	3 hr
Aug 12, 4:00 PM EDT	Areal Flood Advisory	RNK	Watauga	3 hr
Aug 12, 4:30 PM EDT	Flash Flood Warning	RNK	Watauga, Wilkes	4 hr

Nearby

Flash Flood Watches in Virginia, 2020 Every flash flood watch in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.