Alert archive / Pennsylvania / Flash Flood Warnings in 2026

Flash Flood Warning 123, NWS Philadelphia/Mount Holly

August 20, 2026New Castle County, Delaware; Camden County, Gloucester County, Salem County, New Jersey; 4 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 20, 2026, 5:39 PM EDT for New Castle County, Delaware; Camden County, Gloucester County, Salem County, New Jersey; 4 counties in Pennsylvania. It was in force for 4 hr. 11 reports 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
Aug 20, 2026, 5:39 PM EDT (21:39 UTC)
Expired
Aug 20, 2026, 9:45 PM EDT
In force
4 hr
Issued by
NWS Philadelphia/Mount Holly
Area
Storm-based polygon
Flood severity
None

Counties New Castle County, DE, Camden County, NJ, Gloucester County, NJ, Salem County, NJ, Chester County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 75 km from the middle of the area, began a volume at 21:43 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

TimeReportWhereRemark
Aug 20, 6:15 PM EDTFLASH FLOODWilmington Manor, DERoad Flooding up to 5 inches deep occurring on East Basin Road near 624 East Basin Road.
Aug 20, 6:30 PM EDTFLASH FLOODDarby, PAFlash flooding, road closures, and water rescues reported in Darby. Time given in report.
Aug 20, 6:30 PM EDTFLASH FLOODLansdowne, PAFlash flooding, road closures, and water rescues reported in Landsdowne. Time given in report.
Aug 20, 6:30 PM EDTFLASH FLOODProspect Park, PACorrects previous flash flood report from Prospect Park. Flash flooding, road closures, and water rescues reported in Prospect Park. Time given in report.
Aug 20, 6:30 PM EDTFLASH FLOODProspect Park, PAFlash flooding, road closures, and water rescues reported in Landsdowne. Time given in report.
Aug 20, 6:30 PM EDTFLASH FLOODRidley Twp., PAWater rescues reported around Ridley Township. Time given in report.
Aug 20, 7:07 PM EDTFLASH FLOOD1 E Willow Grove, PAStorm dropped 2 inches of rain resulting in street flooding.
Aug 20, 7:44 PM EDTFLASH FLOODBrooklawn, NJFlooding on US 130 Both Directions At CR 551 (Brooklawn), All lanes closed southbound; All lanes closed northbound.
Aug 20, 8:51 PM EDTRAIN 1.071 Ne Midvale, DEASOS station KILG Wilmington.
Aug 20, 9:00 PM EDTRAIN 21 E Willow Grove, PAMesonet station EW1527 Willow Grove.
Aug 20, 9:15 PM EDTFLASH FLOOD1 Wnw Flourtown, PAThe Wissahickon Creek at Fort Washington went into Flood Stage.

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 12:00Z, 9.7 hours before the alert went out and 212 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-pSkew-T log-p diagram, Washington/Dulle, VA at 12:00Z on 2026-08-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 97 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 12:00Z on 2026-08-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 115 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
97 J/kg
Mixed-layer CIN
-72 J/kg
Mixed-layer LCL
1192 m above ground
0-6 km bulk shear
47 kt
0-1 km storm-relative helicity
115 m²/s²
0-3 km storm-relative helicity
230 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.0

Open this sounding in Storm Lab

The text

As transmitted.

060 
WGUS51 KPHI 202139
FFWPHI
DEC003-NJC007-015-033-PAC029-045-091-101-210145-
/O.NEW.KPHI.FF.W.0123.260820T2139Z-260821T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
539 PM EDT Thu Aug 20 2026

The National Weather Service in Mount Holly has issued a

* Flash Flood Warning for...
  Northern New Castle County in northern Delaware...
  Northwestern Camden County in southern New Jersey...
  Northwestern Gloucester County in southern New Jersey...
  Northwestern Salem County in southern New Jersey...
  Southeastern Chester County in southeastern Pennsylvania...
  Delaware County in southeastern Pennsylvania...
  Southeastern Montgomery County in southeastern Pennsylvania...
  Philadelphia County in southeastern Pennsylvania...

* Until 945 PM EDT.

* At 539 PM EDT, Doppler radar indicated thunderstorms producing
  heavy rain across the warned area. Up to 0.5 inches of rain have
  fallen. The expected rainfall rate is 1.5 to 2.5 inches in 1 hour.
  Additional rainfall amounts of 1 to 2 inches are possible in the
  warned area. Flash flooding is ongoing or expected to begin
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar indicated.

  IMPACT...Flash flooding of small creeks and streams, urban areas,
           highways, streets and underpasses as well as other poor
           drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Philadelphia, Camden, Wilmington, Newark, West Chester, Gloucester
  City, Chester, West Deptford, Yeadon and Westtown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3972 7587 3979 7579 4001 7558 4009 7537
      4015 7511 4014 7503 4012 7496 4008 7496
      4006 7498 4005 7497 4002 7501 4001 7505
      3999 7506 4000 7503 3998 7501 3984 7515
      3971 7543 3957 7578 3972 7579

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...1.5-2.5 INCHES IN 1 HOUR

$$

Hoeflich
3 follow-up statements
648 
WGUS71 KPHI 202242
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
642 PM EDT Thu Aug 20 2026

DEC003-NJC007-015-033-PAC029-045-091-101-210145-
/O.CON.KPHI.FF.W.0123.000000T0000Z-260821T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
New Castle DE-Camden NJ-Gloucester NJ-Salem NJ-Chester PA-
Delaware PA-Montgomery PA-Philadelphia PA-
642 PM EDT Thu Aug 20 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 945 PM EDT THIS
EVENING FOR NORTHERN NEW CASTLE, NORTHWESTERN CAMDEN, NORTHWESTERN
GLOUCESTER, NORTHWESTERN SALEM, SOUTHEASTERN CHESTER, DELAWARE,
SOUTHEASTERN MONTGOMERY AND PHILADELPHIA COUNTIES...

At 642 PM EDT, trained weather spotters reported thunderstorms
producing heavy rain with water rescues around Delaware County.
Between 1 and 2 inches of rain have fallen. The expected rainfall
rate is 0.5 inches in 1 hour. Additional rainfall amounts up to 0.5
inches are possible in the warned area. Flash flooding is already
occurring.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Trained spotters reported.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Philadelphia, Camden, Wilmington, Newark, West Chester, Gloucester
  City, Chester, West Deptford, Yeadon and Westtown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3972 7587 3979 7579 4001 7558 4009 7537
      4015 7511 4014 7503 4012 7496 4008 7496
      4006 7498 4005 7497 4002 7501 4001 7505
      3999 7506 4000 7503 3998 7501 3984 7515
      3971 7543 3957 7578 3972 7579

FLASH FLOOD...OBSERVED
EXPECTED RAINFALL RATE...0.5 INCHES IN 1 HOUR

$$
902 
WGUS71 KPHI 210039
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
839 PM EDT Thu Aug 20 2026

DEC003-NJC007-015-033-PAC029-045-091-101-210145-
/O.CON.KPHI.FF.W.0123.000000T0000Z-260821T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
New Castle DE-Camden NJ-Gloucester NJ-Salem NJ-Chester PA-
Delaware PA-Montgomery PA-Philadelphia PA-
839 PM EDT Thu Aug 20 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 945 PM EDT THIS
EVENING FOR NORTHERN NEW CASTLE, NORTHWESTERN CAMDEN, NORTHWESTERN
GLOUCESTER, NORTHWESTERN SALEM, SOUTHEASTERN CHESTER, DELAWARE,
SOUTHEASTERN MONTGOMERY AND PHILADELPHIA COUNTIES...

At 839 PM EDT, trained weather spotters reported flash flooding with
water rescues around Delaware County. Between 1 and 2.5 inches of
rain have fallen. Flooding impacts will continue, but no additional
rainfall is expected. Flash flooding is already occurring.

HAZARD...Flash flooding caused by heavy rain.

SOURCE...Trained spotters reported.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Philadelphia, Camden, Wilmington, Newark, West Chester, Gloucester
  City, Chester, West Deptford, Yeadon and Westtown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3972 7587 3979 7579 4001 7558 4009 7537
      4015 7511 4014 7503 4012 7496 4008 7496
      4006 7498 4005 7497 4002 7501 4001 7505
      3999 7506 4000 7503 3998 7501 3984 7515
      3971 7543 3957 7578 3972 7579

FLASH FLOOD...OBSERVED

$$

Hoeflich
723 
WGUS71 KPHI 210138
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
938 PM EDT Thu Aug 20 2026

DEC003-NJC007-015-033-PAC029-045-091-101-210148-
/O.EXP.KPHI.FF.W.0123.000000T0000Z-260821T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
New Castle DE-Camden NJ-Gloucester NJ-Salem NJ-Chester PA-
Delaware PA-Montgomery PA-Philadelphia PA-
938 PM EDT Thu Aug 20 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 945 PM EDT THIS EVENING FOR
NORTHERN NEW CASTLE, NORTHWESTERN CAMDEN, NORTHWESTERN GLOUCESTER,
NORTHWESTERN SALEM, SOUTHEASTERN CHESTER, DELAWARE, SOUTHEASTERN
MONTGOMERY AND PHILADELPHIA COUNTIES...

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

&&

LAT...LON 3972 7587 3979 7579 4001 7558 4009 7537
      4015 7511 4014 7503 4012 7496 4008 7496
      4006 7498 4005 7497 4002 7501 4001 7505
      3999 7506 4000 7503 3998 7501 3984 7515
      3971 7543 3957 7578 3972 7579

$$

Hoeflich

The office that day

Everything else NWS Philadelphia/Mount Holly issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 20, 4:16 PM EDTTornado WarningPHIKent29 min
Aug 20, 4:50 PM EDTSevere Thunderstorm Warning Considerable damage threatPHINew Castle40 min
Aug 20, 5:27 PM EDTSevere Thunderstorm Warning Considerable damage threatPHINew Castle48 min
Aug 20, 5:39 PM EDTTornado WarningPHIKent36 min
Aug 20, 5:40 PM EDTSevere Thunderstorm WarningPHIKent50 min
Aug 20, 6:03 PM EDTTornado WarningPHIKent42 min
Aug 20, 6:09 PM EDTSevere Thunderstorm WarningPHIKent, New Castle51 min
Aug 20, 6:13 PM EDTSevere Thunderstorm WarningPHINew Castle47 min
Aug 20, 6:21 PM EDTSevere Thunderstorm WarningPHIKent, Sussex39 min
Aug 20, 6:53 PM EDTFlash Flood Warning Considerable damage threatPHIKent105 min
Aug 20, 6:57 PM EDTSevere Thunderstorm WarningPHIKent, Sussex48 min
Aug 20, 2:04 PM EDTSpecial Marine WarningPHI86 min
Aug 20, 3:26 PM EDTSpecial Marine WarningPHI94 min
Aug 20, 4:38 PM EDTTornado WarningPHIAtlantic37 min
Aug 20, 4:41 PM EDTFlash Flood WarningPHIAtlantic, Cape May, Cumberland4 hr
Aug 20, 5:13 PM EDTSpecial Marine WarningPHI92 min
Aug 20, 5:14 PM EDTSpecial Marine WarningPHI91 min
Aug 20, 5:24 PM EDTFlash Flood WarningPHIAtlantic4 hr
Aug 20, 5:36 PM EDTSpecial Marine WarningPHI84 min
Aug 20, 6:15 PM EDTSpecial Marine WarningPHI60 min
Aug 20, 6:26 PM EDTFlash Flood WarningPHIMercer4 hr
Aug 20, 6:30 PM EDTSpecial Marine WarningPHI90 min
Aug 20, 6:38 PM EDTSevere Thunderstorm WarningPHIAtlantic, Cape May, Cumberland37 min
Aug 20, 6:44 PM EDTSpecial Marine WarningPHI61 min
Aug 20, 7:01 PM EDTTornado WarningPHIAtlantic, Cape May, Cumberland29 min
Aug 20, 7:08 PM EDTTornado Warning Tornado observedPHICape May22 min
Aug 20, 7:10 PM EDTSevere Thunderstorm WarningPHIAtlantic, Cape May, Cumberland50 min
Aug 20, 7:37 PM EDTSpecial Marine WarningPHI2 hr
Aug 20, 7:43 PM EDTSpecial Marine WarningPHI2 hr
Aug 20, 4:59 PM EDTSevere Thunderstorm Warning Destructive damage threatPHIChester46 min
Aug 20, 5:22 PM EDTTornado WarningPHIChester, Delaware38 min

Nearby

Flash Flood Warnings in Pennsylvania, 2026Flash Flood Warnings in New Jersey, 2026Flash Flood Warnings in Delaware, 2026Every flash flood warning in 2026

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.