Alert archive / Pennsylvania / Flash Flood Warnings in 2026

Flash Flood Warning 59, NWS Philadelphia/Mount Holly

July 21, 2026Chester County, Delaware County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Jul 21, 2026, 4:31 PM EDT for Chester County, Delaware County, Pennsylvania. It was in force for 96 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Jul 21, 2026, 4:31 PM EDT (20:31 UTC)
Expired: Jul 21, 2026, 6:07 PM EDT
In force: 96 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Chester County, PA, Delaware County, PA

The radar

The Dover AFB radar (KDOX), 122 km from the middle of the area, began a volume at 20:30 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, 8.5 hours before the alert went out and 164 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: 941 J/kg
Mixed-layer CIN: -113 J/kg
Mixed-layer LCL: 772 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 68 m²/s²
0-3 km storm-relative helicity: 112 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 0.9

Open this sounding in Storm Lab

The text

As transmitted.

381 
WGUS51 KPHI 212031
FFWPHI
PAC029-045-220030-
/O.NEW.KPHI.FF.W.0059.260721T2031Z-260722T0030Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
431 PM EDT Tue Jul 21 2026

The National Weather Service in Mount Holly has issued a

* Flash Flood Warning for...
  Southern Chester County in southeastern Pennsylvania...
  Western Delaware County in southeastern Pennsylvania...

* Until 830 PM EDT.

* At 431 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1.5 and 2.5 inches of 
  rain have fallen. The expected rainfall rate is 1 to 2 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.

  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...
  West Chester, Coatesville, Westtown, Downingtown, Kennett Square, 
  Oxford, Parkesburg, West Grove, Cochranville, Marshallton, 
  Homeville and Mount Vernon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4005 7560 4002 7553 3990 7554 3982 7574
      3974 7585 3972 7588 3972 7614 3974 7612
      3973 7609 3975 7610 3976 7606 3983 7604
      3983 7602 3985 7602 3987 7599 3993 7600
      3993 7598 3995 7599 3998 7598 4004 7567

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

$$

Hoeflich

1 follow-up statement

068 
WGUS71 KPHI 212207
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
607 PM EDT Tue Jul 21 2026

PAC029-045-212217-
/O.CAN.KPHI.FF.W.0059.000000T0000Z-260722T0030Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Chester PA-Delaware PA-
607 PM EDT Tue Jul 21 2026

...FLASH FLOOD WARNING IS CANCELLED FOR SOUTHERN CHESTER AND WESTERN 
DELAWARE COUNTIES...

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

A Flood Watch remains in effect until 200 AM EDT Wednesday for 
portions of northern Delaware, New Jersey, and southeast 
Pennsylvania.

&&

LAT...LON 4005 7560 4002 7553 3990 7554 3982 7574
      3974 7585 3972 7588 3972 7614 3974 7612
      3973 7609 3975 7610 3976 7606 3983 7604
      3983 7602 3985 7602 3987 7599 3993 7600
      3993 7598 3995 7599 3998 7598 4004 7567

$$

Hoeflich

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 21, 2:18 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh	42 min
Jul 21, 2:57 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Lehigh, Northampton	37 min
Jul 21, 3:37 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	53 min
Jul 21, 3:47 PM EDT	Severe Thunderstorm Warning	PHI	Carbon, Monroe	43 min
Jul 21, 3:58 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	47 min
Jul 21, 4:23 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	52 min
Jul 21, 4:38 PM EDT	Flash Flood Warning Considerable damage threat	PHI	Chester, Delaware, Montgomery, Philadelphia	4 hr
Jul 21, 4:43 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	47 min
Jul 21, 5:30 PM EDT	Severe Thunderstorm Warning	PHI	Delaware	45 min

Nearby

Flash Flood Warnings in Pennsylvania, 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.