Alert archive / Virginia / Flash Flood Watches in 2021

Flash Flood Watch 10, NWS Baltimore/Washington

August 17, 202132 counties in Virginia; 9 counties in Maryland; 8 counties in West Virginia

NWS Baltimore/Washington issued this flash flood watch at Aug 17, 2021, 1:54 PM EDT for 32 counties in Virginia; 9 counties in Maryland; 8 counties in West Virginia. It took effect at Aug 17, 2021, 8:00 PM EDT. It was in force for 21 hr.

The area

The counties it named.

The facts

Issued: Aug 17, 2021, 1:54 PM EDT (17:54 UTC)
In effect from: Aug 17, 2021, 8:00 PM EDT
Expired: Aug 18, 2021, 4:42 PM EDT
In force: 21 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

All 49 counties

Allegany County, MD, Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Washington 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 Fredericksburg, VA, City of Harrisonburg, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, Highland 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, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Pendleton County, WV

The radar

The Sterling radar (KLWX), 57 km from the middle of the area, began a volume at 17:55 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, 5.9 hours before the alert went out and 63 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: 226 J/kg
Mixed-layer CIN: -58 J/kg
Mixed-layer LCL: 577 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 83 m²/s²
0-3 km storm-relative helicity: 81 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.7

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 17, 9:38 AM EDT, 4 hours 16 minutes earlier.

Area forecast discussion, Aug 17, 9:38 AM EDT, 4 hours 16 minutes before

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Hazardous weather outlook, Aug 17, 9:02 AM EDT, 4 hours 52 minutes before

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The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 16, 8:17 PM EDT	Areal Flood Warning	LWX	Albemarle, Nelson	7 hr
Aug 16, 8:57 PM EDT	Areal Flood Warning	LWX	Albemarle, Greene, Madison, Rappahannock	6 hr
Aug 16, 9:10 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Nelson	3 hr
Aug 16, 9:21 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Albemarle, Greene, Madison, Rappahannock	3 hr
Aug 16, 11:32 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Arlington, Fairfax	3 hr
Aug 16, 11:47 PM EDT	Special Marine Warning	LWX		88 min
Aug 17, 12:09 AM EDT	Areal Flood Warning	LWX	Loudoun	4 hr
Aug 17, 1:10 AM EDT	Special Marine Warning	LWX		50 min
Aug 17, 1:59 AM EDT	Special Marine Warning	LWX		86 min
Aug 17, 2:17 AM EDT	Areal Flood Warning	LWX	Arlington, Fairfax	4 hr
Aug 17, 2:20 AM EDT	Special Marine Warning	LWX		65 min
Aug 17, 8:07 AM EDT	Special Marine Warning	LWX		83 min
Aug 17, 8:34 AM EDT	Small Craft Advisory	LWX		5 hr
Aug 17, 8:50 AM EDT	Special Marine Warning	LWX		115 min
Aug 17, 9:31 AM EDT	Special Marine Warning	LWX		85 min
Aug 17, 1:18 PM EDT	Small Craft Advisory	LWX		33 hr
Aug 17, 6:10 PM EDT	Special Marine Warning	LWX		70 min
Aug 16, 8:47 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Washington	2 hr
Aug 16, 9:04 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Allegany	2 hr
Aug 17, 12:39 AM EDT	Coastal Flood Advisory	LWX	Anne Arundel	100 min
Aug 17, 8:54 AM EDT	Flash Flood Watch	LWX	Anne Arundel, Baltimore, Cecil, Harford, City of Baltimore	9 hr
Aug 17, 6:40 PM EDT	Coastal Flood Advisory	LWX	Anne Arundel, Baltimore, City of Baltimore	11 hr

Nearby

Flash Flood Watches in Virginia, 2021 Flash Flood Watches in Maryland, 2021 Flash Flood Watches in West Virginia, 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.