Alert archive / Maryland / Flash Flood Watches in 2021

Flash Flood Watch 16, NWS Baltimore/Washington

September 8, 20216 counties in Virginia; 10 counties in Maryland

NWS Baltimore/Washington issued this flash flood watch at Sep 8, 2021, 6:11 PM EDT for 6 counties in Virginia; 10 counties in Maryland. It took effect at Sep 8, 2021, 8:00 PM EDT. It was in force for 8 hr.

The area

The counties it named.

The facts

Issued: Sep 8, 2021, 6:11 PM EDT (22:11 UTC)
In effect from: Sep 8, 2021, 8:00 PM EDT
Expired: Sep 9, 2021, 4:00 AM EDT
In force: 8 hr
Issued by: NWS Baltimore/Washington
Flood severity: None

Counties Anne Arundel County, MD, Baltimore County, MD, Carroll County, MD, Cecil County, MD, City of Baltimore, MD, Frederick County, 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, Loudoun County, VA

The radar

The Sterling radar (KLWX), 51 km from the middle of the area, began a volume at 22:14 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, 10.2 hours before the alert went out and 46 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1137 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 127 m²/s²
0-3 km storm-relative helicity: 137 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 Sep 8, 3:21 PM EDT, 2 hours 50 minutes earlier.

Area forecast discussion, Sep 8, 3:21 PM EDT, 2 hours 50 minutes before

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Hazardous weather outlook, Sep 8, 4:58 PM EDT, 1 hour 13 minutes before

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In the hours before

Local storm report, Sep 8, 3:38 PM EDT, 2 hours 33 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
338 PM EDT WED SEP 08 2021

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

0300 PM     HAIL             2 NW NINDE              38.30N  77.08W
09/08/2021  M0.75 INCH       KING GEORGE        VA   TRAINED SPOTTER

            DIME SIZE HAIL

&&

EVENT NUMBER LWX2105867

KLW

Local storm report, Sep 8, 4:04 PM EDT, 2 hours 7 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
404 PM EDT WED SEP 08 2021

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

0355 PM     MARINE TSTM WIND 8 E SMITH ISLAND        37.97N  75.88W
09/08/2021  E39 MPH          ANZ543             MD   BUOY

            CRS

&&

EVENT NUMBER LWX2105868

DH

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 7, 10:48 PM EDT	Small Craft Advisory	LWX		27 hr
Sep 8, 2:11 PM EDT	Special Marine Warning	LWX		69 min
Sep 8, 2:40 PM EDT	Special Marine Warning	LWX		95 min
Sep 8, 2:58 PM EDT	Severe Thunderstorm Warning	LWX	King George	14 min
Sep 7, 10:46 PM EDT	Coastal Flood Advisory	LWX	Anne Arundel, Baltimore, Harford, City of Baltimore	12 hr
Sep 8, 2:28 PM EDT	Coastal Flood Advisory	LWX	Anne Arundel, Baltimore, Harford, City of Baltimore	11 hr

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.