Alert archive / Virginia / Flash Flood Warnings in 2020

Flash Flood Warning 21, NWS Baltimore/Washington

July 23, 2020Prince William County, Virginia

NWS Baltimore/Washington issued this flash flood warning at Jul 23, 2020, 9:46 PM EDT for Prince William County, Virginia. It was in force for 4 hr. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Jul 23, 2020, 9:46 PM EDT (01:46 UTC)
Expired: Jul 24, 2020, 1:45 AM EDT
In force: 4 hr
Issued by: NWS Baltimore/Washington
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Prince William County, VA

The radar

The Sterling radar (KLWX), 44 km from the middle of the area, began a volume at 01:49 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.

What was reported inside it

Time	Report	Where	Remark
Jul 23, 9:49 PM EDT	FLASH FLOOD	Cherry Hill, VA	SEVERAL VEHICLES SUBMERGED IN HIGH WATER REQUIRING A WATER RESCUE ON CHERRY HILL ROAD BY THE CSX RAILROAD TRACKS.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 1.8 hours before the alert went out and 38 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: 229 J/kg
Mixed-layer CIN: -13 J/kg
Mixed-layer LCL: 2029 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 10 m²/s²
0-3 km storm-relative helicity: 26 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

696 
WGUS51 KLWX 240146
FFWLWX
VAC153-240545-
/O.NEW.KLWX.FF.W.0021.200724T0146Z-200724T0545Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Baltimore MD/Washington DC
946 PM EDT Thu Jul 23 2020

The National Weather Service in Sterling Virginia has issued a

* Flash Flood Warning for...
  Southeastern Prince William County in northern Virginia...

* Until 145 AM EDT.

* At 945 PM EDT, Doppler radar indicated thunderstorms producing
  heavy rain across the area. Up to two inches of rain have already
  fallen. Rain of one to two inches is expected in the next hour.
  Flash flooding is ongoing or expected to begin shortly.

  HAZARD...Life threatening flash flooding. Heavy rain producing 
           flash flooding.

  SOURCE...Radar indicated.

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

* Some locations that may experience flooding include...
  Dale City...                      Woodbridge...
  Lake Ridge...                     Montclair...
  Lorton...                         Dumfries...
  Cherry Hill...                    Independent Hill...
  Mason Neck...                     Occoquan...

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.

A Flash Flood Warning means that flooding is imminent or occurring.
If you are in the warned area move to higher ground immediately.
Residents living along streams and creeks should take immediate
precautions to protect life and property.

&&

LAT...LON 3862 7722 3858 7725 3856 7724 3855 7724
      3859 7741 3870 7738 3868 7725 3866 7723
      3866 7721

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL...1-2 INCHES IN 1 HOUR

$$

BKF

2 follow-up statements

561 
WGUS71 KLWX 240257
FFSLWX

Flash Flood Statement
National Weather Service Baltimore MD/Washington DC
1057 PM EDT Thu Jul 23 2020

VAC153-240545-
/O.CON.KLWX.FF.W.0021.000000T0000Z-200724T0545Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Prince William VA-
1057 PM EDT Thu Jul 23 2020

...THE FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 145 AM EDT FOR
SOUTHEASTERN PRINCE WILLIAM COUNTY...

At 1056 PM EDT, emergency management reported flash flooding in s 
outheastern Prince William County, including along Cherry Hill Road 
where several vehicles were trapped in high water. Even though the 
heaviest rain has ended, flooding is still ongoing.

HAZARD...Flash flooding caused by heavy rain.

SOURCE...Emergency management.

IMPACT...Flooding of small creeks and streams, urban areas, 
         highways, streets and underpasses as well as other drainage 
         and low lying areas.

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 3862 7722 3858 7725 3856 7724 3855 7724
      3859 7741 3870 7738 3868 7725 3866 7723
      3866 7721

FLASH FLOOD...OBSERVED

$$

DHOF

053 
WGUS71 KLWX 240537
FFSLWX

Flash Flood Statement
National Weather Service Baltimore MD/Washington DC
137 AM EDT Fri Jul 24 2020

VAC153-240546-
/O.EXP.KLWX.FF.W.0021.000000T0000Z-200724T0545Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Prince William VA-
137 AM EDT Fri Jul 24 2020

...THE FLASH FLOOD WARNING FOR SOUTHEASTERN PRINCE WILLIAM COUNTY
WILL EXPIRE AT 145 AM EDT...

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

LAT...LON 3862 7722 3858 7725 3856 7724 3855 7724
      3859 7741 3870 7738 3868 7725 3866 7723
      3866 7721

$$

KJP

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 23, 8:13 PM EDT	Flash Flood Watch	LWX	Arlington, Fairfax, City of Alexandria, City of Fairfax, City of Falls Church	4 hr
Jul 23, 8:28 PM EDT	Areal Flood Warning	LWX	Fairfax, Prince William, City of Alexandria, City of Fairfax, City of Falls Church, City of Manassas and 1 more	5 hr
Jul 23, 8:46 PM EDT	Severe Thunderstorm Warning	LWX	Arlington, Fairfax, Prince William, City of Alexandria, City of Falls Church	44 min
Jul 23, 9:45 PM EDT	Special Marine Warning	LWX		29 min
Jul 23, 9:46 PM EDT	Special Marine Warning	LWX		33 min
Jul 23, 10:14 PM EDT	Areal Flood Warning	LWX	Arlington	4 hr
Jul 23, 10:36 PM EDT	Special Marine Warning	LWX		45 min
Jul 24, 3:33 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier	13 min
Jul 24, 3:58 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, Orange	47 min
Jul 24, 4:28 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Orange	21 min
Jul 24, 4:42 PM EDT	Special Marine Warning	LWX		81 min
Jul 24, 5:08 PM EDT	Special Marine Warning	LWX		82 min
Jul 24, 5:42 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, Nelson, City of Charlottesville	48 min
Jul 24, 6:10 PM EDT	Special Marine Warning	LWX		74 min

Nearby

Flash Flood Warnings in Virginia, 2020 Every flash flood warning in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.