Alert archive / Pennsylvania / Flash Flood Warnings in 2023

Flash Flood Warning 45, NWS Philadelphia/Mount Holly

July 9, 2023Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Jul 9, 2023, 4:31 PM EDT for Chester County, Montgomery County, Pennsylvania. It was in force for 4 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: Jul 9, 2023, 4:31 PM EDT (20:31 UTC)
Expired: Jul 9, 2023, 8:30 PM EDT
In force: 4 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 107 km from the middle of the area, began a volume at 20:34 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 9, 4:36 PM EDT	FLOOD	Downington, PA	Report of minor street flooding at intersection of Rte 322 and Lancaster Ave. Time estimated.
Jul 9, 5:32 PM EDT	FLOOD	1 Nnw Uwchlan Twp, PA	Trained spotter measures water in Pine Creek area at 4.1 feet and rushing. Measured with a crest gauge that was in place. Water started to flood into parking area at time of report. Flooding now into yards and basements.
Jul 9, 5:38 PM EDT	FLOOD	1 Wsw Chester Springs, PA	Report of flooding near Pickering Creek in West Pikeland Twp.
Jul 9, 7:15 PM EDT	FLASH FLOOD	2 Nne Marshallton, PA	The Brandywine Creek gauge at Downingtown reached minor 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, 8.5 hours before the alert went out and 192 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: 952 J/kg
Mixed-layer CIN: -58 J/kg
Mixed-layer LCL: 686 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: 12 m²/s²
0-3 km storm-relative helicity: 37 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

As transmitted.

882 
WGUS51 KPHI 092031
FFWPHI
PAC029-091-100030-
/O.NEW.KPHI.FF.W.0045.230709T2031Z-230710T0030Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
431 PM EDT Sun Jul 9 2023

The National Weather Service in Mount Holly has issued a

* Flash Flood Warning for...
  Central Chester County in southeastern Pennsylvania...
  Northwestern Montgomery County in southeastern Pennsylvania...

* Until 830 PM EDT.

* At 431 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 0.5 and 1.5 inches of 
  rain have fallen. 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, Phoenixville, Coatesville, Westtown, Downingtown, 
  Kennett Square, Collegeville, Royersford, Parkesburg, Trappe, West 
  Grove, and Schwenksville.

This includes the following highways...
	Pennsylvania Turnpike between mile markers 305 and 321.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3983 7564 3976 7583 3995 7592 4002 7589
      4011 7580 4020 7561 4035 7553 4033 7542
      4009 7549 3997 7549

FLASH FLOOD...RADAR INDICATED

$$

Hoeflich

1 follow-up statement

028 
WGUS71 KPHI 100021
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
821 PM EDT Sun Jul 9 2023

PAC029-091-100031-
/O.EXP.KPHI.FF.W.0045.000000T0000Z-230710T0030Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Chester PA-Montgomery PA-
821 PM EDT Sun Jul 9 2023

...FLASH FLOOD WARNING WILL EXPIRE AT 830 PM EDT THIS EVENING FOR 
CENTRAL CHESTER AND NORTHWESTERN MONTGOMERY COUNTIES...

Flood waters have receded. The heavy rain has ended. Flooding is no 
longer expected to pose a threat.

A Flood Watch remains in effect until 1200 AM EDT for portions of 
east central Pennsylvania...northeast Pennsylvania...and southeast 
Pennsylvania.

A Flood Watch remains in effect until 1200 AM EDT for portions of 
northern Delaware...northeast Maryland...southern New Jersey...and 
southeast Pennsylvania.

LAT...LON 3983 7564 3976 7583 3995 7592 4002 7589
      4011 7580 4020 7561 4035 7553 4033 7542
      4009 7549 3997 7549

$$

Hoeflich

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 9, 11:00 AM EDT	Special Weather Statement	PHI	Carbon	30 min
Jul 9, 11:33 AM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery	8 hr
Jul 9, 11:47 AM EDT	Special Weather Statement	PHI	Monroe	43 min
Jul 9, 11:49 AM EDT	Special Weather Statement	PHI	Montgomery	41 min
Jul 9, 11:54 AM EDT	Areal Flood Advisory	PHI	Berks, Bucks, Lehigh, Montgomery	33 min
Jul 9, 12:14 PM EDT	Special Weather Statement	PHI	Bucks	46 min
Jul 9, 12:15 PM EDT	Special Weather Statement	PHI	Monroe	30 min
Jul 9, 12:22 PM EDT	Special Weather Statement	PHI	Lebanon	38 min
Jul 9, 12:27 PM EDT	Flash Flood Warning	PHI	Berks, Bucks, Lehigh, Montgomery	8 hr
Jul 9, 12:37 PM EDT	Areal Flood Advisory	PHI	Bucks, Lehigh, Northampton	2 hr
Jul 9, 12:43 PM EDT	Areal Flood Advisory	PHI	Berks	33 min
Jul 9, 12:51 PM EDT	Special Weather Statement	PHI	Northampton	24 min
Jul 9, 12:57 PM EDT	Areal Flood Advisory	PHI	Carbon, Monroe	6 hr
Jul 9, 1:02 PM EDT	Flash Flood Warning	PHI	Bucks, Lehigh, Northampton	8 hr
Jul 9, 1:16 PM EDT	Flash Flood Warning	PHI	Berks	6 hr
Jul 9, 1:17 PM EDT	Special Weather Statement	PHI	Berks	28 min
Jul 9, 1:32 PM EDT	Areal Flood Advisory	PHI	Carbon, Lehigh, Monroe, Northampton	4 hr
Jul 9, 2:16 PM EDT	Areal Flood Advisory	PHI	Berks, Lehigh	30 min
Jul 9, 2:41 PM EDT	Flash Flood Warning	PHI	Berks	4 hr
Jul 9, 2:46 PM EDT	Flash Flood Warning	PHI	Berks, Lehigh, Northampton	6 hr
Jul 9, 3:01 PM EDT	Special Weather Statement	PHI	Berks	29 min
Jul 9, 3:03 PM EDT	Special Weather Statement	PHI	Chester	27 min
Jul 9, 3:15 PM EDT	Severe Thunderstorm Warning	PHI	Berks	30 min
Jul 9, 3:20 PM EDT	Special Weather Statement	PHI	Berks	25 min
Jul 9, 3:27 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester	33 min
Jul 9, 3:41 PM EDT	Special Weather Statement	PHI	Berks	34 min
Jul 9, 3:51 PM EDT	Flash Flood Warning Considerable damage threat	PHI	Berks, Chester, Lehigh, Montgomery	6 hr
Jul 9, 3:59 PM EDT	Special Weather Statement	PHI	Chester	31 min
Jul 9, 4:03 PM EDT	Severe Thunderstorm Warning	PHI	Montgomery	27 min
Jul 9, 4:19 PM EDT	Special Weather Statement	PHI	Chester	26 min
Jul 9, 5:10 PM EDT	Severe Thunderstorm Warning	PHI	Delaware	50 min
Jul 9, 5:12 PM EDT	Flash Flood Warning	PHI	Bucks, Montgomery	5 hr
Jul 9, 5:15 PM EDT	Special Weather Statement	PHI	Bucks, Delaware, Philadelphia	30 min
Jul 9, 5:31 PM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	4 hr
Jul 9, 5:35 PM EDT	Severe Thunderstorm Warning	PHI	Philadelphia	25 min
Jul 9, 5:59 PM EDT	Flash Flood Warning	PHI	Bucks, Montgomery	4 hr
Jul 9, 6:05 PM EDT	Special Weather Statement	PHI	Bucks	25 min
Jul 9, 7:04 PM EDT	Areal Flood Warning	PHI	Berks	9 hr
Jul 9, 7:11 PM EDT	Areal Flood Advisory	PHI	Bucks	3 hr
Jul 9, 7:27 PM EDT	River Flood Warning	PHI	Chester	4 hr

Nearby

Flash Flood Warnings in Pennsylvania, 2023 Every flash flood warning in 2023

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.