Alert archive / Maryland / Flash Flood Warnings in 2021

Flash Flood Warning 42, NWS Baltimore/Washington

August 16, 2021Allegany County, Maryland

NWS Baltimore/Washington issued this flash flood warning at Aug 16, 2021, 9:04 PM EDT for Allegany County, Maryland. It was in force for 2 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 16, 2021, 9:04 PM EDT (01:04 UTC)
Expired: Aug 16, 2021, 11:14 PM EDT
In force: 2 hr
Issued by: NWS Baltimore/Washington
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Allegany County, MD

The radar

The Sterling radar (KLWX), 116 km from the middle of the area, began a volume at 01:05 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, 1.1 hours before the alert went out and 124 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: 376 J/kg
Mixed-layer CIN: -9 J/kg
Mixed-layer LCL: 504 m above ground
0-6 km bulk shear: 11 kt
0-1 km storm-relative helicity: 24 m²/s²
0-3 km storm-relative helicity: 34 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

778 
WGUS51 KLWX 170104
FFWLWX
MDC001-170400-
/O.NEW.KLWX.FF.W.0042.210817T0104Z-210817T0400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Baltimore MD/Washington DC
904 PM EDT Mon Aug 16 2021

The National Weather Service in Sterling Virginia has issued a

* Flash Flood Warning for...
  Northeastern Allegany County in western Maryland...

* Until midnight EDT.

* At 904 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1 and 3 inches of rain 
  have fallen. Additional rainfall amounts of 1 to 2 inches are 
  possible in the warned area. Flash flooding is ongoing or expected 
  to begin shortly.

  HAZARD...Life threatening flash flooding. Thunderstorms
           producing flash flooding.

  SOURCE...Radar.

  IMPACT...Life threatening flash flooding of creeks and streams,
           urban areas, highways, streets and underpasses.

* Some locations that will experience flash flooding include...
  Pumpkin Center...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

&&

LAT...LON 3972 7838 3970 7839 3965 7843 3960 7848
      3958 7855 3957 7868 3962 7867 3968 7857
      3972 7853 3972 7852 3972 7851 3972 7847
      3972 7845 3972 7844 3972 7843 3972 7841

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

BJL

2 follow-up statements

869 
WGUS71 KLWX 170203
FFSLWX

Flash Flood Statement
National Weather Service Baltimore MD/Washington DC
1003 PM EDT Mon Aug 16 2021

MDC001-170400-
/O.CON.KLWX.FF.W.0042.000000T0000Z-210817T0400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Allegany MD-
1003 PM EDT Mon Aug 16 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL MIDNIGHT EDT TONIGHT 
FOR NORTHEASTERN ALLEGANY COUNTY...

At 1003 PM EDT, Doppler radar indicated that between 3 and 5 inches 
of rain have fallen over most of the warned area. The heaviest rain 
has ended, but creeks and streams will continue to rise due to 
excess runoff. Flash flooding is ongoing or expected to begin 
shortly.

HAZARD...Life threatening flash flooding. Thunderstorms producing
         flash flooding.

SOURCE...Radar.

IMPACT...Life threatening flash flooding of creeks and streams,
         urban areas, highways, streets and underpasses.

Some locations that will experience flash flooding include...
  Pumpkin Center...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

&&

LAT...LON 3972 7838 3970 7839 3965 7843 3960 7848
      3958 7855 3957 7868 3962 7867 3968 7857
      3972 7853 3972 7852 3972 7851 3972 7847
      3972 7845 3972 7844 3972 7843 3972 7841

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

BJL

850 
WGUS71 KLWX 170314
FFSLWX

Flash Flood Statement
National Weather Service Baltimore MD/Washington DC
1114 PM EDT Mon Aug 16 2021

MDC001-170324-
/O.CAN.KLWX.FF.W.0042.000000T0000Z-210817T0400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Allegany MD-
1114 PM EDT Mon Aug 16 2021

...FLASH FLOOD WARNING IS CANCELLED FOR NORTHEASTERN ALLEGANY 
COUNTY...

Flood waters have receded. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures.

LAT...LON 3972 7838 3970 7839 3965 7843 3960 7848
      3958 7855 3957 7868 3962 7867 3968 7857
      3972 7853 3972 7852 3972 7851 3972 7847
      3972 7845 3972 7844 3972 7843 3972 7841

$$

BRO

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 16, 8:47 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Washington	2 hr
Aug 16, 11:32 PM EDT	Flash Flood Warning Considerable damage threat	LWX	Montgomery	3 hr
Aug 17, 12:39 AM EDT	Coastal Flood Advisory	LWX	Anne Arundel	100 min
Aug 17, 2:17 AM EDT	Areal Flood Warning	LWX	Montgomery	4 hr
Aug 17, 8:54 AM EDT	Flash Flood Watch	LWX	Anne Arundel, Baltimore, Cecil, Harford, City of Baltimore	9 hr
Aug 17, 1:54 PM EDT	Flash Flood Watch	LWX	Allegany, Baltimore, Carroll, Frederick, Harford, Howard and 3 more	27 hr
Aug 17, 6:40 PM EDT	Coastal Flood Advisory	LWX	Anne Arundel, Baltimore, City of Baltimore	11 hr

Nearby

Flash Flood Warnings in Maryland, 2021 Every flash flood warning 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.