Alert archive / Pennsylvania / Flash Flood Warnings in 2026

Flash Flood Warning 1, NWS Philadelphia/Mount Holly

May 20, 2026Burlington County, Camden County, Gloucester County, New Jersey; 4 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at May 20, 2026, 5:40 PM EDT for Burlington County, Camden County, Gloucester County, New Jersey; 4 counties in Pennsylvania. It was in force for 3 hr. 2 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: May 20, 2026, 5:40 PM EDT (21:40 UTC)
Expired: May 20, 2026, 8:35 PM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Burlington County, NJ, Camden County, NJ, Gloucester County, NJ, Bucks County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 70 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

Time	Report	Where	Remark
May 20, 6:00 PM EDT	FLASH FLOOD	Trout Lake, PA	Flooding on I-476 northbound 1.2 miles north of Exit 9: PA 3 - BROOMALL/UPPER DARBY. There is a lane restriction. Time given in report.
May 20, 6:00 PM EDT	FLASH FLOOD	Trout Lake, PA	Flooding on I-476 northbound 1.2 miles north of Exit 9: PA 3 - BROOMALL/UPPER DARBY. There is a lane restriction. Time given in report.

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 220 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: 47 J/kg
Mixed-layer CIN: -204 J/kg
Mixed-layer LCL: 1752 m above ground
0-6 km bulk shear: 23 kt
0-1 km storm-relative helicity: -79 m²/s²
0-3 km storm-relative helicity: -47 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

862 
WGUS51 KPHI 202140
FFWPHI
NJC005-007-015-PAC017-045-091-101-210145-
/O.NEW.KPHI.FF.W.0001.260520T2140Z-260521T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
540 PM EDT Wed May 20 2026

The National Weather Service in Mount Holly has issued a

* Flash Flood Warning for...
  Northwestern Burlington County in southern New Jersey...
  Northwestern Camden County in southern New Jersey...
  North Central Gloucester County in southern New Jersey...
  Southeastern Bucks 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 540 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 to 2 inches in 1 hour. 
  Additional rainfall amounts of 0.5 to 1.5 inches are possible in 
  the warned area. Flash flooding is ongoing or expected to begin 
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar.

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

* Some locations that may experience flash flooding include...
  Philadelphia, Camden, Gloucester City, Bensalem, Chester, 
  Bellmawr, Yeadon, Burlington, Bristol, Riverside, Conshohocken and 
  Palmyra.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4018 7503 4013 7480 4000 7497 3998 7498
      3996 7504 3987 7509 3985 7527 3984 7543
      3993 7552 3997 7546 3998 7545 3999 7544
      3999 7545 4000 7544 4012 7524

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...1-2 INCHES IN 1 HOUR

$$

Hoeflich

1 follow-up statement

400 
WGUS71 KPHI 210035
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
835 PM EDT Wed May 20 2026

NJC005-007-015-PAC017-045-091-101-210045-
/O.CAN.KPHI.FF.W.0001.000000T0000Z-260521T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Burlington NJ-Camden NJ-Gloucester NJ-Bucks PA-Delaware PA-
Montgomery PA-Philadelphia PA-
835 PM EDT Wed May 20 2026

...FLASH FLOOD WARNING IS CANCELLED FOR NORTHWESTERN BURLINGTON, 
NORTHWESTERN CAMDEN, NORTH CENTRAL GLOUCESTER, SOUTHEASTERN BUCKS, 
DELAWARE, SOUTHEASTERN MONTGOMERY AND PHILADELPHIA COUNTIES...

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

&&

LAT...LON 4018 7503 4013 7480 4000 7497 3998 7498
      3996 7504 3987 7509 3985 7527 3984 7543
      3993 7552 3997 7546 3998 7545 3999 7544
      3999 7545 4000 7544 4012 7524

$$

Fitzsimmons

The office that day

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

Issued	Product	Office	Counties	Lasted
May 20, 2:25 PM EDT	Small Craft Advisory	PHI		3 days
May 20, 4:43 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Warren	47 min
May 20, 5:01 PM EDT	Special Marine Warning	PHI		86 min
May 20, 5:10 PM EDT	Severe Thunderstorm Warning	PHI	Camden, Gloucester	50 min
May 20, 5:15 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Hunterdon, Mercer, Somerset	45 min
May 20, 5:24 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Middlesex, Morris, Somerset, Warren	51 min
May 20, 5:29 PM EDT	Severe Thunderstorm Warning	PHI	Camden, Gloucester, Salem	46 min
May 20, 5:35 PM EDT	Severe Thunderstorm Warning	PHI	Salem	40 min
May 20, 5:41 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Mercer, Monmouth, Ocean	49 min
May 20, 5:52 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Hunterdon, Mercer, Middlesex, Monmouth, Ocean and 1 more	38 min
May 20, 6:01 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Camden, Gloucester	44 min
May 20, 6:04 PM EDT	Severe Thunderstorm Warning Considerable damage threat	PHI	Hunterdon, Middlesex, Monmouth, Morris, Somerset	56 min
May 20, 6:07 PM EDT	Special Marine Warning	PHI		53 min
May 20, 6:09 PM EDT	Severe Thunderstorm Warning	PHI	Atlantic, Burlington, Camden, Gloucester, Ocean	46 min
May 20, 6:12 PM EDT	Severe Thunderstorm Warning	PHI	Ocean	33 min
May 20, 6:17 PM EDT	Special Marine Warning	PHI		118 min
May 20, 6:23 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Mercer, Middlesex, Monmouth, Ocean, Somerset	56 min
May 20, 6:58 PM EDT	Severe Thunderstorm Warning	PHI	Ocean	32 min
May 20, 7:30 PM EDT	Special Marine Warning	PHI		90 min
May 19, 8:04 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	25 min
May 20, 3:57 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh	48 min
May 20, 4:00 PM EDT	Severe Thunderstorm Warning	PHI	Berks	45 min
May 20, 4:29 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester, Montgomery	46 min
May 20, 4:46 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Lehigh, Montgomery	44 min
May 20, 4:50 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	40 min

Nearby

Flash Flood Warnings in Pennsylvania, 2026 Flash Flood Warnings in New Jersey, 2026 Every 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.