Alert archive / Virginia / Flash Flood Watches in 2011

Flash Flood Watch 3, NWS Baltimore/Washington

April 27, 201126 counties in Virginia; 11 counties in Maryland; 8 counties in West Virginia

NWS Baltimore/Washington issued this flash flood watch at Apr 27, 2011, 9:51 AM EDT for 26 counties in Virginia; 11 counties in Maryland; 8 counties in West Virginia. It took effect at Apr 27, 2011, 10:00 PM EDT. It was in force for 17 hr.

The area

The counties it named.

The facts

Issued: Apr 27, 2011, 9:51 AM EDT (13:51 UTC)
In effect from: Apr 27, 2011, 10:00 PM EDT
Expired: Apr 28, 2011, 3:00 PM EDT
In force: 17 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

All 45 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, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford 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), 43 km from the middle of the area, began a volume at 13:51 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, 1.9 hours before the alert went out and 49 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: 215 J/kg
Mixed-layer CIN: -75 J/kg
Mixed-layer LCL: 636 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 123 m²/s²
0-3 km storm-relative helicity: 150 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.8

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 Apr 27, 2:55 AM EDT, 6 hours 56 minutes earlier.

Area forecast discussion, Apr 27, 2:55 AM EDT, 6 hours 56 minutes before

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Hazardous weather outlook, Apr 27, 4:27 AM EDT, 5 hours 24 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
Apr 26, 8:45 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Rockingham, Shenandoah	45 min
Apr 26, 9:01 PM EDT	Tornado Warning	LWX	Frederick, Shenandoah	29 min
Apr 26, 9:31 PM EDT	Severe Thunderstorm Warning	LWX	Clarke, Frederick, Shenandoah, City of Winchester	9 min
Apr 26, 9:32 PM EDT	Special Weather Statement	LWX	Shenandoah	28 min
Apr 27, 10:11 AM EDT	Gale Warning	LWX		29 hr
Apr 27, 2:13 PM EDT	Small Craft Advisory	LWX		29 hr
Apr 27, 2:51 PM EDT	Special Marine Warning	LWX		39 min
Apr 27, 2:54 PM EDT	Special Weather Statement	LWX	Albemarle, Nelson, City of Charlottesville	51 min
Apr 27, 3:01 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, Nelson	44 min
Apr 27, 3:28 PM EDT	Special Marine Warning	LWX		47 min
Apr 27, 3:43 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, Orange	47 min
Apr 27, 3:54 PM EDT	Special Marine Warning	LWX		26 min
Apr 27, 4:15 PM EDT	Special Weather Statement	LWX	City of Charlottesville	30 min
Apr 27, 4:30 PM EDT	Special Weather Statement	LWX	Orange	30 min
Apr 27, 4:39 PM EDT	Special Marine Warning	LWX		96 min
Apr 27, 4:44 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Orange, Spotsylvania	46 min
Apr 27, 4:50 PM EDT	Special Weather Statement	LWX	Madison	25 min
Apr 27, 5:08 PM EDT	Tornado Warning	LWX	Orange, Spotsylvania	37 min
Apr 27, 5:30 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, Orange, Spotsylvania, Stafford	45 min
Apr 27, 5:46 PM EDT	Tornado Warning	LWX	Prince William, Spotsylvania, Stafford	29 min
Apr 27, 5:47 PM EDT	Special Weather Statement	LWX	Culpeper	28 min
Apr 27, 5:48 PM EDT	Special Marine Warning	LWX		57 min
Apr 27, 6:08 PM EDT	Tornado Warning	LWX	Fairfax, Prince William, Stafford	37 min
Apr 27, 6:17 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax, Prince William	43 min
Apr 27, 6:26 PM EDT	Special Weather Statement	LWX	Stafford	34 min
Apr 27, 6:42 PM EDT	Special Marine Warning	LWX		63 min
Apr 27, 6:47 PM EDT	Severe Thunderstorm Warning	LWX	Nelson	14 min
Apr 27, 6:59 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, City of Charlottesville	33 min
Apr 27, 7:00 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax, Prince William	32 min
Apr 27, 7:19 PM EDT	Special Weather Statement	LWX	Orange	26 min
Apr 27, 7:21 PM EDT	Flash Flood Warning	LWX	Fairfax, Prince William	69 min
Apr 27, 7:27 PM EDT	Severe Thunderstorm Warning	LWX	Greene, Madison, Orange	25 min
Apr 27, 7:28 PM EDT	Special Marine Warning	LWX		65 min
Apr 27, 7:36 PM EDT	Special Weather Statement	LWX	Culpeper	24 min
Apr 27, 7:42 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, Rappahannock	21 min
Apr 26, 8:38 PM EDT	Special Weather Statement	LWX	Allegany	37 min
Apr 26, 8:50 PM EDT	Severe Thunderstorm Warning	LWX	Allegany	22 min
Apr 26, 8:52 PM EDT	Tornado Warning	LWX	Allegany	19 min
Apr 27, 2:56 PM EDT	Special Weather Statement	LWX	Saint Mary's	34 min
Apr 27, 3:16 PM EDT	Special Weather Statement	LWX	Saint Mary's	29 min
Apr 27, 3:37 PM EDT	Special Weather Statement	LWX	Calvert	23 min
Apr 27, 6:38 PM EDT	Tornado Warning	LWX	Charles, Prince George's	37 min
Apr 27, 7:08 PM EDT	Tornado Warning	LWX	Anne Arundel, Prince George's	37 min
Apr 27, 7:16 PM EDT	Special Weather Statement	LWX	Carroll	29 min
Apr 27, 7:24 PM EDT	Tornado Warning	LWX	Charles, Prince George's	36 min
Apr 27, 7:27 PM EDT	Special Weather Statement	LWX	Howard	33 min
Apr 27, 7:31 PM EDT	Tornado Warning	LWX	Baltimore, Carroll, Howard	29 min
Apr 27, 7:34 PM EDT	Tornado Warning	LWX	Anne Arundel, Prince George's	26 min
Apr 26, 8:01 PM EDT	Severe Thunderstorm Warning	LWX	Grant, Hardy, Pendleton	44 min
Apr 26, 8:32 PM EDT	Special Weather Statement	LWX	Pendleton	28 min

Nearby

Flash Flood Watches in Virginia, 2011 Flash Flood Watches in Maryland, 2011 Flash Flood Watches in West Virginia, 2011 Every flash flood watch in 2011

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.