Alert archive / Pennsylvania / Flash Flood Warnings in 2021

Flash Flood Warning 62, NWS Philadelphia/Mount Holly

August 28, 2021Delaware County, Montgomery County, Philadelphia County, Pennsylvania; Gloucester County, New Jersey

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 28, 2021, 11:57 AM EDT for Delaware County, Montgomery County, Philadelphia County, Pennsylvania; Gloucester County, New Jersey. It was in force for 3 hr. 4 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 28, 2021, 11:57 AM EDT (15:57 UTC)
Expired: Aug 28, 2021, 2:59 PM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Gloucester County, NJ, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 72 km from the middle of the area, began a volume at 16:00 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
Aug 28, 12:45 PM EDT	FLOOD	1 Sse Montgomeryville, PA	FLOODING AT INTERSECTION OF PA-309 AT GARDEN GOLF BOULEVARD.
Aug 28, 12:45 PM EDT	FLOOD	2 W West Conshohocken, PA	FLOODING ON I-76 EASTBOUND AT MILE POST 330.
Aug 28, 12:45 PM EDT	FLASH FLOOD	Tinicum Twp, PA	SIGNIFICANT FLOODING JUST SOUTH OF I-95 NEAR PHILADELPHIA INTERNATIONAL AIRPORT. MULTIPLE LANES CLOSED.
Aug 28, 12:50 PM EDT	FLASH FLOOD	1 Wsw Temple University, PA	SEVERAL STREETS FLOODED OVER PORTIONS OF NORTH PHILLY NEAR TEMPLE, INCLUDING SEYBERT ST NEAR RIDGE AVENUE. WATER OVER THE CURBS.

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, 4.0 hours before the alert went out and 219 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: 425 J/kg
Mixed-layer CIN: -107 J/kg
Mixed-layer LCL: 898 m above ground
0-6 km bulk shear: 9 kt
0-1 km storm-relative helicity: -11 m²/s²
0-3 km storm-relative helicity: 11 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

219 
WGUS51 KPHI 281557
FFWPHI
NJC015-PAC045-091-101-282000-
/O.NEW.KPHI.FF.W.0062.210828T1557Z-210828T2000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
1157 AM EDT Sat Aug 28 2021

The National Weather Service in Mount Holly has issued a

* Flash Flood Warning for...
  North Central Gloucester County in southern New Jersey...
  Northeastern Delaware County in southeastern Pennsylvania...
  Southeastern Montgomery County in southeastern Pennsylvania...
  Western Philadelphia County in southeastern Pennsylvania...

* Until 400 PM EDT.

* At 1157 AM EDT, Doppler radar indicated heavy rain across portions 
  of the warned area. Between 1 and 1.5 inches of rain have fallen. 
  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 heavy rain.

  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, Gloucester City, Norristown, Deptford, West 
  Deptford, Lansdale, West Norriton, East Norriton, Yeadon, 
  Woodbury, Conshohocken, and Folcroft.

This includes the following highways...
	Pennsylvania Turnpike between mile markers 328 and 341.
	Interstate 95 in Pennsylvania between mile markers 10 and 22.
	Interstate 76 in Pennsylvania between mile markers 329 and 351.
	Interstate 295 in New Jersey between mile markers 16 and 25.
	Interstate 676 in Pennsylvania between mile markers 0 and 1.
	Interstate 476 in Pennsylvania between mile markers 14 and 19.
	Northeast Extension between mile markers 21 and 29.

This includes the following streams and drainages...
  Crosswicks-Neshaminy, Schuylkill, and Lower Delaware.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4007 7536 4013 7542 4019 7547 4027 7525
      4021 7514 3989 7514 3978 7509 3977 7508
      3975 7526

FLASH FLOOD...RADAR INDICATED

$$

Kruzdlo

1 follow-up statement

800 
WGUS71 KPHI 281859
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
259 PM EDT Sat Aug 28 2021

NJC015-PAC045-091-101-281909-
/O.CAN.KPHI.FF.W.0062.000000T0000Z-210828T2000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Gloucester NJ-Delaware PA-Montgomery PA-Philadelphia PA-
259 PM EDT Sat Aug 28 2021

...FLASH FLOOD WARNING IS CANCELLED FOR NORTH CENTRAL GLOUCESTER, 
NORTHEASTERN DELAWARE, SOUTHEASTERN MONTGOMERY, AND WESTERN 
PHILADELPHIA COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat.

Flash flooding was reported earlier near Temple University and 
around Philadelphia International Airport.

LAT...LON 4007 7536 4013 7542 4019 7547 4027 7525
      4021 7514 3989 7514 3978 7509 3977 7508
      3975 7526

$$

Kruzdlo

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 28, 2:47 AM EDT	Areal Flood Advisory	PHI	Berks	2 hr
Aug 28, 3:06 AM EDT	Areal Flood Advisory	PHI	Chester, Delaware, Montgomery, Philadelphia	2 hr
Aug 28, 4:06 AM EDT	Flash Flood Warning	PHI	Berks	3 hr
Aug 28, 8:07 AM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery, Northampton	3 hr
Aug 28, 9:06 AM EDT	Flash Flood Warning	PHI	Bucks, Montgomery, Northampton	3 hr
Aug 27, 10:46 PM EDT	Areal Flood Advisory	PHI	Cape May	119 min
Aug 28, 3:11 AM EDT	Special Marine Warning	PHI		64 min
Aug 28, 11:58 AM EDT	Areal Flood Advisory	PHI	Atlantic, Cape May	3 hr

Nearby

Flash Flood Warnings in Pennsylvania, 2021 Flash Flood Warnings in New Jersey, 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.