Alert archive / Maryland / Flash Flood Watches in 2021

Flash Flood Watch 12, NWS Baltimore/Washington

August 27, 20215 counties in Virginia; 8 counties in Maryland

NWS Baltimore/Washington issued this flash flood watch at Aug 27, 2021, 2:56 AM EDT for 5 counties in Virginia; 8 counties in Maryland. It took effect at Aug 27, 2021, 1:00 PM EDT. It was in force for 7 hr.

The area

The counties it named.

The facts

Issued: Aug 27, 2021, 2:56 AM EDT (06:56 UTC)
In effect from: Aug 27, 2021, 1:00 PM EDT
Expired: Aug 27, 2021, 7:44 PM EDT
In force: 7 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

Counties Anne Arundel County, MD, Baltimore County, MD, Cecil County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Montgomery County, 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), 58 km from the middle of the area, began a volume at 06:57 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

Roanoke, VA (KRNK), launched 00:00Z, 6.9 hours before the alert went out and 314 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: 1725 J/kg
Mixed-layer CIN: -11 J/kg
Mixed-layer LCL: 1093 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: 36 m²/s²
0-3 km storm-relative helicity: 51 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 26, 9:46 PM EDT, 5 hours 10 minutes earlier.

Area forecast discussion, Aug 26, 9:46 PM EDT, 5 hours 10 minutes before

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Hazardous weather outlook, Aug 26, 9:11 PM EDT, 5 hours 45 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 27, 3:01 PM EDT	Special Marine Warning	LWX		79 min
Aug 27, 3:05 PM EDT	Severe Thunderstorm Warning	LWX	Arlington, Fairfax, City of Falls Church	40 min
Aug 27, 3:36 PM EDT	Severe Thunderstorm Warning Considerable damage threat	LWX	Arlington, Fairfax	19 min
Aug 27, 4:11 PM EDT	Areal Flood Warning	LWX	Arlington, Fairfax, City of Fairfax, City of Falls Church	3 hr
Aug 27, 4:44 PM EDT	Areal Flood Warning	LWX	Arlington, Fairfax, City of Alexandria	3 hr
Aug 27, 4:46 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax	44 min
Aug 27, 4:48 PM EDT	Special Marine Warning	LWX		66 min
Aug 27, 4:57 PM EDT	Special Marine Warning	LWX		70 min
Aug 27, 5:21 PM EDT	Severe Thunderstorm Warning	LWX	Fairfax, Prince William	39 min
Aug 27, 5:44 PM EDT	Areal Flood Warning	LWX	Fairfax, City of Alexandria	2 hr
Aug 27, 6:30 PM EDT	Special Marine Warning	LWX		71 min
Aug 27, 7:07 PM EDT	Special Marine Warning	LWX		55 min
Aug 27, 2:35 PM EDT	Severe Thunderstorm Warning	LWX	Montgomery	40 min
Aug 27, 3:25 PM EDT	Severe Thunderstorm Warning	LWX	Frederick	30 min
Aug 27, 4:14 PM EDT	Severe Thunderstorm Warning	LWX	Carroll, Frederick	46 min
Aug 27, 4:59 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel	33 min
Aug 27, 5:06 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Carroll	20 min
Aug 27, 5:52 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Harford	53 min
Aug 27, 6:10 PM EDT	Severe Thunderstorm Warning	LWX	Charles	32 min
Aug 27, 6:11 PM EDT	Areal Flood Warning	LWX	Charles, Prince George's	3 hr
Aug 27, 6:13 PM EDT	Areal Flood Warning	LWX	Baltimore, Harford	3 hr
Aug 27, 6:17 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Harford	29 min
Aug 27, 6:28 PM EDT	Severe Thunderstorm Warning	LWX	Calvert, Charles, Prince George's, Saint Mary's	47 min

Nearby

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