Alert archive / Virginia / Flash Flood Watches in 2012

Flash Flood Watch 6, NWS Baltimore/Washington

July 20, 201228 counties in Virginia; 11 counties in Maryland; 8 counties in West Virginia

NWS Baltimore/Washington issued this flash flood watch at Jul 20, 2012, 4:26 AM EDT for 28 counties in Virginia; 11 counties in Maryland; 8 counties in West Virginia. It took effect at Jul 20, 2012, 12:00 PM EDT. It was in force for 10 hr.

The area

The counties it named.

The facts

Issued: Jul 20, 2012, 4:26 AM EDT (08:26 UTC)
In effect from: Jul 20, 2012, 12:00 PM EDT
Expired: Jul 20, 2012, 9:30 PM EDT
In force: 10 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

All 47 counties

Allegany County, MD, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Prince George's County, MD, Saint Mary's County, MD, Washington County, MD, Arlington 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, King George County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Rappahannock 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), 44 km from the middle of the area, began a volume at 08:28 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, 8.4 hours before the alert went out and 50 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: 525 J/kg
Mixed-layer CIN: -20 J/kg
Mixed-layer LCL: 1690 m above ground
0-6 km bulk shear: 16 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: 47 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 Jul 20, 4:15 AM EDT, 11 minutes earlier.

Area forecast discussion, Jul 20, 4:15 AM EDT, 11 minutes before

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Hazardous weather outlook, Jul 20, 1:49 AM EDT, 2 hours 37 minutes before

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In the hours before

Special weather statement, Jul 19, 10:45 PM EDT, 5 hours 41 minutes before

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Local storm report, Jul 19, 11:08 PM EDT, 5 hours 18 minutes before

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Local storm report, Jul 19, 11:37 PM EDT, 4 hours 49 minutes before

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Local storm report, Jul 19, 11:56 PM EDT, 4 hours 30 minutes before

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Special weather statement, Jul 20, 1:06 AM EDT, 3 hours 20 minutes before

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Local storm report, Jul 20, 3:00 AM EDT, 1 hour 26 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
Jul 19, 8:43 PM EDT	Special Weather Statement	LWX	Loudoun	47 min
Jul 19, 9:07 PM EDT	Special Marine Warning	LWX		83 min
Jul 19, 9:16 PM EDT	Special Marine Warning	LWX		38 min
Jul 19, 9:28 PM EDT	Special Weather Statement	LWX	Arlington, Fairfax, City of Alexandria, City of Fairfax, City of Falls Church, City of Manassas and 1 more	47 min
Jul 19, 9:34 PM EDT	Severe Thunderstorm Warning	LWX	Arlington, Fairfax, Prince William, City of Alexandria, City of Fairfax, City of Falls Church and 1 more	41 min
Jul 19, 9:58 PM EDT	Special Marine Warning	LWX		92 min
Jul 19, 10:20 PM EDT	Special Weather Statement	LWX	City of Alexandria	25 min
Jul 19, 10:24 PM EDT	Flash Flood Warning	LWX	Arlington, City of Alexandria	3 hr
Jul 19, 10:26 PM EDT	Special Marine Warning	LWX		25 min
Jul 19, 10:31 PM EDT	Special Marine Warning	LWX		82 min
Jul 19, 10:36 PM EDT	Special Marine Warning	LWX		114 min
Jul 19, 11:04 PM EDT	Special Marine Warning	LWX		86 min
Jul 19, 11:07 PM EDT	Special Marine Warning	LWX		78 min
Jul 20, 7:11 PM EDT	Special Weather Statement	LWX	City of Manassas Park	49 min
Jul 20, 7:44 PM EDT	Flash Flood Warning	LWX	Fairfax, Fauquier, Loudoun, Prince William	85 min
Jul 19, 9:20 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Howard, Montgomery, Prince George's	40 min
Jul 19, 9:49 PM EDT	Special Weather Statement	LWX	Howard	26 min
Jul 19, 10:01 PM EDT	Special Weather Statement	LWX	Howard	29 min
Jul 19, 10:06 PM EDT	Flash Flood Warning	LWX	Anne Arundel, Baltimore, City of Baltimore	3 hr
Jul 19, 10:17 PM EDT	Flash Flood Warning	LWX	Baltimore, Carroll	3 hr
Jul 19, 10:45 PM EDT	Special Weather Statement	LWX	Anne Arundel, Prince George's	45 min
Jul 19, 11:16 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Calvert, Prince George's	29 min
Jul 20, 1:06 AM EDT	Special Weather Statement	LWX	City of Baltimore	24 min
Jul 20, 3:36 PM EDT	Special Weather Statement	LWX	Allegany	39 min
Jul 20, 6:19 PM EDT	Special Weather Statement	LWX	Grant, Hardy	41 min
Jul 20, 6:59 PM EDT	Special Weather Statement	LWX	Hardy	46 min
Jul 20, 7:03 PM EDT	Flash Flood Warning	LWX	Grant, Hardy, Pendleton	115 min

Nearby

Flash Flood Watches in Virginia, 2012 Flash Flood Watches in Maryland, 2012 Flash Flood Watches in West Virginia, 2012 Every flash flood watch in 2012

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.