Alert archive / Virginia / Flash Flood Watches in 2021

Flash Flood Watch 15, NWS Baltimore/Washington

August 30, 202125 counties in Virginia; 8 counties in Maryland

NWS Baltimore/Washington issued this flash flood watch at Aug 30, 2021, 11:48 AM EDT for 25 counties in Virginia; 8 counties in Maryland. It took effect at Aug 30, 2021, 2:00 PM EDT. It was in force for 3 hr.

The area

The counties it named.

The facts

Issued: Aug 30, 2021, 11:48 AM EDT (15:48 UTC)
In effect from: Aug 30, 2021, 2:00 PM EDT
Expired: Aug 30, 2021, 5:24 PM EDT
In force: 3 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

All 33 counties

Anne Arundel County, MD, Baltimore County, MD, Charles County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Albemarle County, VA, Amherst County, VA, Arlington County, VA, Augusta County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Harrisonburg, VA, City of Staunton, VA, City of Waynesboro, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Greene County, VA, Loudoun County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Rappahannock County, VA, Rockbridge County, VA, Rockingham County, VA, Stafford County, VA, Warren County, VA

The radar

The Sterling radar (KLWX), 54 km from the middle of the area, began a volume at 15:49 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 12:00Z, 3.8 hours before the alert went out and 57 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: 843 J/kg
Mixed-layer CIN: -70 J/kg
Mixed-layer LCL: 860 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: 65 m²/s²
0-3 km storm-relative helicity: 63 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 Baltimore/Washington wrote its last area forecast discussion before this flash flood watch went out at Aug 30, 9:08 AM EDT, 2 hours 40 minutes earlier.

Area forecast discussion, Aug 30, 9:08 AM EDT, 2 hours 40 minutes before

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Hazardous weather outlook, Aug 30, 8:43 AM EDT, 3 hours 5 minutes before

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In the hours before

Local storm report, Aug 30, 10:47 AM EDT, 1 hour 1 minute before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1047 AM EDT MON AUG 30 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0950 PM     FLOOD            GORDONSVILLE            38.14N  78.19W
08/28/2021                   ORANGE             VA   NWS EMPLOYEE

            WATER A COUPLE OF INCHES DEEP NEAR 200 N MAIN ST.

&&

EVENT NUMBER LWX2105736

KLW

The office that day

Everything else NWS Baltimore/Washington issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 30, 4:54 AM EDT	Flash Flood Watch	LWX	Albemarle, Amherst, Arlington, Augusta, Clarke, Culpeper and 27 more	62 hr
Aug 30, 2:39 PM EDT	Severe Thunderstorm Warning	LWX	Augusta, Rockingham, City of Harrisonburg	51 min
Aug 30, 2:54 PM EDT	Special Marine Warning	LWX		48 min
Aug 30, 3:59 PM EDT	Severe Thunderstorm Warning	LWX	Fauquier, Prince William, City of Manassas	33 min
Aug 30, 4:01 PM EDT	Special Marine Warning	LWX		119 min
Aug 30, 4:16 PM EDT	Severe Thunderstorm Warning	LWX	Augusta	15 min
Aug 30, 4:29 PM EDT	Severe Thunderstorm Warning	LWX	Fauquier, Prince William, Stafford, City of Manassas	17 min
Aug 30, 5:30 PM EDT	Special Marine Warning	LWX		2 hr
Aug 30, 6:09 PM EDT	Special Marine Warning	LWX		96 min
Aug 30, 7:00 PM EDT	Special Marine Warning	LWX		90 min
Aug 30, 7:53 PM EDT	Special Marine Warning	LWX		18 min
Aug 30, 6:04 PM EDT	Severe Thunderstorm Warning	LWX	Charles, Saint Mary's	25 min
Aug 30, 7:17 AM EDT	Dense Fog Advisory	LWX	Berkeley, Grant, Hampshire, Hardy, Jefferson, Mineral and 1 more	103 min

Nearby

Flash Flood Watches in Virginia, 2021 Flash Flood Watches in Maryland, 2021 Every flash flood watch in 2021

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.