Alert archive / Virginia / Flash Flood Watches in 2011

Flash Flood Watch 13, NWS Baltimore/Washington

August 21, 20115 counties in Virginia; 5 counties in Maryland

NWS Baltimore/Washington issued this flash flood watch at Aug 21, 2011, 11:10 AM EDT for 5 counties in Virginia; 5 counties in Maryland. It took effect at Aug 21, 2011, 2:00 PM EDT. It was in force for 5 hr.

The area

The counties it named.

The facts

Issued: Aug 21, 2011, 11:10 AM EDT (15:10 UTC)
In effect from: Aug 21, 2011, 2:00 PM EDT
Expired: Aug 21, 2011, 6:34 PM EDT
In force: 5 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

Counties Anne Arundel County, MD, Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Prince George's County, MD, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, Fairfax County, VA

The radar

The Sterling radar (KLWX), 46 km from the middle of the area, began a volume at 15:11 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, 3.2 hours before the alert went out and 40 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: 1589 J/kg
Mixed-layer CIN: -99 J/kg
Mixed-layer LCL: 969 m above ground
0-6 km bulk shear: 37 kt
0-1 km storm-relative helicity: 131 m²/s²
0-3 km storm-relative helicity: 125 m²/s²
Significant tornado parameter: 0.6
Supercell composite: 4.9

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 21, 11:05 AM EDT, 5 minutes earlier.

Area forecast discussion, Aug 21, 11:05 AM EDT, 5 minutes before

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Hazardous weather outlook, Aug 21, 9:47 AM EDT, 1 hour 23 minutes before

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In the hours before

Special weather statement, Aug 21, 7:54 AM EDT, 3 hours 16 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
754 AM EDT SUN AUG 21 2011

MDZ006-007-011-211230-
NORTHERN BALTIMORE MD-HARFORD MD-SOUTHERN BALTIMORE MD-
754 AM EDT SUN AUG 21 2011

...STRONG THUNDERSTORM TO AFFECT NORTHERN BALTIMORE...HARFORD AND
SOUTHERN BALTIMORE COUNTIES...

AT 754 AM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 2 MILES
NORTHWEST OF CHASE...MOVING EAST AT 35 MPH.

LOCATIONS IMPACTED INCLUDE PERRYMAN...ABERDEEN AND HAVRE DE GRACE.

WIND GUSTS OF 40 TO 50 MPH CAN BE EXPECTED WITH THIS STORM.

&&

LAT...LON 3944 7606 3940 7616 3934 7622 3937 7626
      3940 7626 3938 7627 3933 7626 3933 7630
      3938 7633 3933 7633 3932 7646 3943 7648
      3957 7609 3954 7608 3950 7611 3948 7606
TIME...MOT...LOC 1154Z 257DEG 29KT 3939 7637

KRAMAR

Special weather statement, Aug 21, 8:04 AM EDT, 3 hours 6 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
804 AM EDT SUN AUG 21 2011

MDZ007-211230-
HARFORD MD-
804 AM EDT SUN AUG 21 2011

...STRONG THUNDERSTORM TO AFFECT HARFORD COUNTY...

AT 805 AM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 2 MILES
SOUTHEAST OF HICKORY...MOVING NORTHEAST AT 30 MPH.

LOCATIONS IMPACTED INCLUDE HAVRE DE GRACE.

WIND GUSTS OF 40 TO 50 MPH CAN BE EXPECTED WITH THIS STORM.

&&

LAT...LON 3950 7632 3960 7640 3969 7620 3965 7615
      3962 7615 3960 7611 3956 7608 3955 7608
TIME...MOT...LOC 1205Z 247DEG 27KT 3957 7627

KRAMAR

Special weather statement, Aug 21, 8:32 AM EDT, 2 hours 38 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
832 AM EDT SUN AUG 21 2011

MDZ007-211300-
HARFORD MD-
832 AM EDT SUN AUG 21 2011

...STRONG THUNDERSTORMS TO AFFECT HARFORD COUNTY...

AT 831 AM EDT...DOPPLER RADAR INDICATED STRONG THUNDERSTORMS ALONG A
LINE EXTENDING FROM HARFORD FURNACE TO ABERDEEN PROVING GROUND...
MOVING NORTHEAST AT 30 MPH.

LOCATIONS IMPACTED INCLUDE HAVRE DE GRACE.

THESE STORMS ARE PRODUCING HEAVY DOWNPOURS AND FREQUENT CLOUD TO
GROUND LIGHTNING. MOVE INDOORS IMMEDIATELY FOR YOUR SAFETY. IF YOU
CAN HEAR THUNDER...YOU ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.

WIND GUSTS OF 35 TO 45 MPH CAN BE EXPECTED WITH THESE STORMS.

&&

LAT...LON 3944 7606 3940 7616 3936 7620 3950 7634
      3963 7631 3969 7621 3965 7615 3962 7615
      3956 7608 3954 7608 3950 7611 3948 7607
      3946 7605
TIME...MOT...LOC 1231Z 228DEG 24KT 3951 7626 3948 7610

JRK

Local storm report, Aug 21, 10:32 AM EDT, 38 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1032 AM EDT SUN AUG 21 2011

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

0557 PM     HAIL             1 ENE CARNEY            39.41N  76.51W
08/19/2011  E1.00 INCH       BALTIMORE          MD   PUBLIC

&&

EVENT NUMBER LWX1101554

JRK

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 21, 4:42 AM EDT	Small Craft Advisory	LWX		44 hr
Aug 21, 7:48 AM EDT	Special Marine Warning	LWX		87 min
Aug 21, 12:05 PM EDT	Severe Thunderstorm Warning	LWX	Augusta, Highland	25 min
Aug 21, 12:18 PM EDT	Special Weather Statement	LWX	Shenandoah	27 min
Aug 21, 12:32 PM EDT	Special Weather Statement	LWX	Augusta	28 min
Aug 21, 12:33 PM EDT	Special Weather Statement	LWX	Clarke, Loudoun	27 min
Aug 21, 12:44 PM EDT	Special Weather Statement	LWX	Page	31 min
Aug 21, 12:54 PM EDT	Special Weather Statement	LWX	Page	36 min
Aug 21, 1:00 PM EDT	Special Weather Statement	LWX	Loudoun	30 min
Aug 21, 1:09 PM EDT	Special Marine Warning	LWX		96 min
Aug 21, 1:12 PM EDT	Severe Thunderstorm Warning	LWX	Fauquier, Loudoun, Prince William	48 min
Aug 21, 1:19 PM EDT	Special Weather Statement	LWX	Fauquier	26 min
Aug 21, 1:24 PM EDT	Severe Thunderstorm Warning	LWX	Fauquier, Loudoun, Prince William	51 min
Aug 21, 1:25 PM EDT	Special Weather Statement	LWX	Page, Rappahannock	35 min
Aug 21, 1:40 PM EDT	Severe Thunderstorm Warning	LWX	Clarke, Loudoun	50 min
Aug 21, 1:50 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax, Fauquier, Loudoun, Prince William	40 min
Aug 21, 1:58 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax, Fauquier, Prince William, City of Manassas	47 min
Aug 21, 2:05 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, Madison, Prince William, Rappahannock, City of Manassas and 1 more	40 min
Aug 21, 2:13 PM EDT	Special Marine Warning	LWX		92 min
Aug 21, 2:17 PM EDT	Special Marine Warning	LWX		118 min
Aug 21, 2:25 PM EDT	Special Weather Statement	LWX	Arlington, Fairfax, City of Alexandria, City of Fairfax, City of Falls Church	35 min
Aug 21, 2:27 PM EDT	Special Marine Warning	LWX		2 hr
Aug 21, 2:28 PM EDT	Special Weather Statement	LWX	Albemarle, City of Charlottesville	32 min
Aug 21, 2:46 PM EDT	Special Marine Warning	LWX		89 min
Aug 21, 2:50 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, City of Charlottesville	21 min
Aug 21, 3:01 PM EDT	Special Weather Statement	LWX	Orange, Prince William, Spotsylvania, Stafford, City of Alexandria, City of Fredericksburg and 2 more	29 min
Aug 21, 3:02 PM EDT	Special Weather Statement	LWX	Arlington, City of Alexandria, City of Falls Church	28 min
Aug 21, 3:11 PM EDT	Severe Thunderstorm Warning	LWX	Arlington	49 min
Aug 21, 3:12 PM EDT	Severe Thunderstorm Warning	LWX	Arlington	48 min
Aug 21, 3:38 PM EDT	Special Marine Warning	LWX		97 min
Aug 21, 4:02 PM EDT	Special Weather Statement	LWX	King George, Spotsylvania, City of Fredericksburg	28 min
Aug 21, 4:11 PM EDT	Special Marine Warning	LWX		94 min
Aug 21, 4:19 PM EDT	Special Marine Warning	LWX		86 min
Aug 21, 4:23 PM EDT	Special Marine Warning	LWX		97 min
Aug 21, 5:39 PM EDT	Special Marine Warning	LWX		96 min
Aug 21, 7:31 PM EDT	Special Marine Warning	LWX		33 min
Aug 21, 7:53 PM EDT	Special Weather Statement	LWX	Albemarle, Arlington, Clarke, Culpeper, Fairfax, Fauquier and 21 more	7 min
Aug 21, 7:54 AM EDT	Special Weather Statement	LWX	Harford	36 min
Aug 21, 8:04 AM EDT	Special Weather Statement	LWX	Harford	26 min
Aug 21, 8:32 AM EDT	Special Weather Statement	LWX	Harford	28 min
Aug 21, 1:11 PM EDT	Special Weather Statement	LWX	Baltimore, City of Baltimore	34 min
Aug 21, 1:14 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Harford, City of Baltimore	46 min
Aug 21, 1:20 PM EDT	Special Weather Statement	LWX	Howard	25 min
Aug 21, 1:28 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Baltimore, Howard, Montgomery, Prince George's	47 min
Aug 21, 1:29 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, City of Baltimore	46 min
Aug 21, 1:39 PM EDT	Flash Flood Warning	LWX	Baltimore, City of Baltimore	3 hr
Aug 21, 1:54 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Baltimore, Harford, City of Baltimore	51 min
Aug 21, 2:01 PM EDT	Tornado Warning	LWX	Anne Arundel	29 min
Aug 21, 2:19 PM EDT	Tornado Warning	LWX	Baltimore	26 min
Aug 21, 2:23 PM EDT	Special Weather Statement	LWX	Howard	37 min
Aug 21, 2:39 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel	36 min
Aug 21, 2:51 PM EDT	Special Weather Statement	LWX	City of Baltimore	24 min
Aug 21, 3:35 PM EDT	Special Weather Statement	LWX	Anne Arundel	25 min
Aug 21, 4:06 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Calvert, Prince George's	39 min
Aug 21, 4:38 PM EDT	Special Weather Statement	LWX	Calvert	37 min
Aug 21, 4:48 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Calvert, Prince George's	27 min
Aug 21, 12:59 PM EDT	Special Weather Statement	LWX	Jefferson	31 min

Nearby

Flash Flood Watches in Virginia, 2011 Flash Flood Watches in Maryland, 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.