Alert archive / Pennsylvania / Flash Flood Warnings in 2018

Flash Flood Warning 59, NWS Philadelphia/Mount Holly

August 11, 2018Delaware County, Philadelphia County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 11, 2018, 1:48 PM EDT for Delaware County, Philadelphia County, Pennsylvania. It was in force for 4 hr. 5 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 11, 2018, 1:48 PM EDT (17:48 UTC)
Expired: Aug 11, 2018, 5:45 PM EDT
In force: 4 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Delaware County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 73 km from the middle of the area, began a volume at 17:47 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 11, 2:08 PM EDT	FLOOD	Haverford Village, PA	HAVERFORD ROAD IS COMPLETELY FLOODED IN ARDMORE TWP.
Aug 11, 2:27 PM EDT	FLASH FLOOD	Prospect Park, PA	TWO VEHICLES STUCK IN WATER WITH WATER RESCUES REQUIRED ON LINCOLN AVENUE.
Aug 11, 2:30 PM EDT	FLASH FLOOD	Germantown, PA	SEVERAL REPORTS OF CARS STUCK IN FLOOD WATERS IN GERMANTOWN...WITH VIDEO SHOWING SWIFTLY FLOWING WATER UP TO THE HOODS OF CARS. PORTIONS OF CHURCH LANE HAD ROAD DAMAGE FROM THE FLOOD WATERS AS WELL. TIME ESTIMATED BASED ON RADAR AND SOCIAL MEDIA REPORTS.
Aug 11, 2:34 PM EDT	FLOOD	Pencoyd, PA	FLOODING ON I-76 WESTBOUND AT EXIT 339.
Aug 11, 2:44 PM EDT	FLOOD	East Oak Lane, PA	PICTURES SHOW A LARGE AREA OF STREET FLOODING IN AND AROUND THE GODFREY AVENUE AND 10TH STREET INTERSECTION.

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, 5.8 hours before the alert went out and 217 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: 963 J/kg
Mixed-layer CIN: -38 J/kg
Mixed-layer LCL: 1021 m above ground
0-6 km bulk shear: 23 kt
0-1 km storm-relative helicity: 59 m²/s²
0-3 km storm-relative helicity: 57 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.6

Open this sounding in Storm Lab

The text

As transmitted.

984 
WGUS51 KPHI 111748
FFWPHI
PAC045-101-112145-
/O.NEW.KPHI.FF.W.0059.180811T1748Z-180811T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
148 PM EDT SAT AUG 11 2018

The National Weather Service in Mount Holly NJ has issued a

* Flash Flood Warning for...
  Philadelphia County in southeastern Pennsylvania...
  Delaware County in southeastern Pennsylvania...

* Until 545 PM EDT.

* At 146 PM EDT, Doppler radar indicated thunderstorms producing 
  heavy rain across southern and central Delaware County moving 
  northeast into Philadelphia County. Rainfall rates over 2 inches 
  per hour are possible in the heaviest rain bands. Flash flooding 
  in the urban areas can be expected.

* Some locations that could experience flooding include...
  Philadelphia, Chester, Yeadon, Folcroft, Swarthmore, East
  Lansdowne, Wissinoming, Darby Township, Cheyney, Morris Park, Bryn
  Mawr, Trout Lake, Tacony, Chelsea, Radnor Township, Gradyville,
  Broomall, Kensington, Newtown Square and Chester Township.

LAT...LON 3993 7554 3998 7544 4000 7545 4004 7541
      4006 7535 3998 7527 4001 7521 4005 7526
      4009 7522 4005 7510 4014 7501 4012 7496
      4009 7496 3997 7509 3996 7513 3986 7521
      3984 7535 3986 7560

$$

jjm

1 follow-up statement

919 
WGUS71 KPHI 112142
FFSPHI

Flash Flood Statement
National Weather Service Mount Holly NJ
542 PM EDT SAT AUG 11 2018

PAC045-101-112151-
/O.EXP.KPHI.FF.W.0059.000000T0000Z-180811T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Philadelphia PA-Delaware PA-
542 PM EDT SAT AUG 11 2018

...THE FLASH FLOOD WARNING FOR PHILADELPHIA AND DELAWARE COUNTIES
WILL EXPIRE AT 545 PM EDT...

Flood waters have receded. While additional rain will be moving into 
the area from the northwest by 600 PM, it is not expected to be 
heavy enough to cause renewed flooding. Please continue to heed any 
remaining road closures.

LAT...LON 3993 7554 3998 7544 4000 7545 4004 7541
      4006 7535 3998 7527 4001 7521 4005 7526
      4009 7522 4005 7510 4014 7501 4012 7496
      4009 7496 3997 7509 3996 7513 3986 7521
      3984 7535 3986 7560

$$

jjm

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 11, 2:25 AM EDT	Special Weather Statement	PHI	Berks	65 min
Aug 11, 3:24 AM EDT	Flash Flood Watch	PHI	Berks, Bucks, Carbon, Chester, Delaware, Lehigh and 4 more	20 hr
Aug 11, 3:26 AM EDT	Special Weather Statement	PHI	Berks	64 min
Aug 11, 4:17 AM EDT	Areal Flood Advisory	PHI	Berks	4 hr
Aug 11, 4:26 AM EDT	Coastal Flood Advisory	PHI	Bucks, Delaware, Philadelphia	24 hr
Aug 11, 5:19 AM EDT	Flash Flood Warning	PHI	Berks	3 hr
Aug 11, 5:27 AM EDT	Areal Flood Advisory	PHI	Northampton	4 hr
Aug 11, 6:06 AM EDT	Areal Flood Advisory	PHI	Bucks, Northampton	6 hr
Aug 11, 6:31 AM EDT	Areal Flood Advisory	PHI	Bucks	7 hr
Aug 11, 12:16 PM EDT	Special Weather Statement	PHI	Chester	29 min
Aug 11, 12:48 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Aug 11, 1:20 PM EDT	Areal Flood Advisory	PHI	Chester, Montgomery	3 hr
Aug 11, 1:33 PM EDT	Flash Flood Warning	PHI	Chester, Montgomery	4 hr
Aug 11, 1:40 PM EDT	Flash Flood Warning	PHI	Chester	4 hr
Aug 11, 1:51 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	39 min
Aug 11, 2:00 PM EDT	Flash Flood Warning	PHI	Bucks, Lehigh, Northampton	9 hr
Aug 11, 2:14 PM EDT	Flash Flood Warning	PHI	Bucks	3 hr
Aug 11, 2:26 PM EDT	Special Weather Statement	PHI	Bucks, Philadelphia	34 min
Aug 11, 2:42 PM EDT	Special Weather Statement	PHI	Bucks	33 min
Aug 11, 3:06 PM EDT	Flash Flood Warning	PHI	Northampton	4 hr
Aug 11, 3:50 PM EDT	Areal Flood Advisory	PHI	Berks, Montgomery	115 min
Aug 11, 4:19 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Aug 11, 4:19 PM EDT	Severe Thunderstorm Warning	PHI	Chester	29 min
Aug 11, 4:47 PM EDT	Special Weather Statement	PHI	Montgomery	28 min
Aug 11, 4:52 PM EDT	Areal Flood Advisory	PHI	Carbon, Lehigh	2 hr
Aug 11, 5:36 PM EDT	Areal Flood Warning	PHI	Bucks	4 hr
Aug 11, 5:58 PM EDT	Areal Flood Advisory	PHI	Chester, Delaware, Montgomery, Philadelphia	5 hr
Aug 11, 6:13 PM EDT	Special Weather Statement	PHI	Chester	32 min

Nearby

Flash Flood Warnings in Pennsylvania, 2018 Every flash flood warning in 2018

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.