Alert archive / Pennsylvania / Flash Flood Warnings in 2009

Flash Flood Warning 64, NWS Philadelphia/Mount Holly

October 24, 2009Chester County, Delaware County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Oct 24, 2009, 5:41 PM EDT for Chester County, Delaware County, Pennsylvania. It was in force for 3 hr. 1 report 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: Oct 24, 2009, 5:41 PM EDT (21:41 UTC)
Expired: Oct 24, 2009, 8:45 PM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Chester County, PA, Delaware County, PA

The radar

The Philadelphia radar (KDIX), 95 km from the middle of the area, began a volume at 21:41 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
Oct 24, 6:30 PM EDT	FLASH FLOOD	2 Sse Valley Forge, PA	SEVERAL ROADWAYS FLOODED IN TREDYFFRIN AND EAST WHITELAND TOWNSHIP INCLUDING PENNSYLVANIA STATE ROUTES 29 AND 30.

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 201 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: 288 J/kg
Mixed-layer CIN: -16 J/kg
Mixed-layer LCL: 586 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 309 m²/s²
0-3 km storm-relative helicity: 369 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 2.7

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

000 
WGUS51 KPHI 242141
FFWPHI
PAC029-045-250045-
/O.NEW.KPHI.FF.W.0064.091024T2141Z-091025T0045Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
541 PM EDT SAT OCT 24 2009

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  EASTERN CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...
  THIS INCLUDES THE CITY OF WEST CHESTER...
  DELAWARE COUNTY IN SOUTHEAST PENNSYLVANIA...

* UNTIL 845 PM EDT

* AT 541 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  FLASH FLOODING FROM A THUNDERSTORM OVER THE WARNED AREA.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO WESTTOWN...
  VALLEY FORGE...TROUT LAKE...NEWTOWN SQUARE...GRADYVILLE...
  CHEYNEY...CHESTER SPRINGS...RADNOR TOWNSHIP...PHOENIXVILLE...
  PAOLI...MARSHALLTON...LIONVILLE...LIMA...DOWNINGTOWN AND BROOMALL

FLOODING MAY ALSO OCCUR ON THE EAST BRANCH OF THE BRANDYWINE CREEK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...COUNTRY ROADS...AS WELL AS FARMLAND ALONG THE
BANKS OF CREEKS AND STREAMS.

&&

LAT...LON 4022 7560 4015 7553 4015 7551 4013 7551
      4013 7548 4009 7545 4010 7543 4007 7541
      4007 7537 4001 7534 4000 7530 3982 7546
      3984 7557 3984 7566 3981 7571 3983 7584

$$

RNS

The office that day

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

Issued	Product	Office	Counties	Lasted
Oct 24, 3:30 PM EDT	Areal Flood Advisory	PHI	Berks, Carbon, Chester, Lehigh, Monroe, Northampton	4 hr
Oct 24, 4:49 PM EDT	Areal Flood Advisory	PHI	Bucks, Delaware, Montgomery, Northampton, Philadelphia	4 hr
Oct 24, 4:55 PM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery	4 hr
Oct 24, 6:02 PM EDT	Flash Flood Warning	PHI	Montgomery	3 hr
Oct 24, 6:28 PM EDT	Severe Thunderstorm Warning	PHI	Bucks	47 min

Nearby

Flash Flood Warnings in Pennsylvania, 2009 Every flash flood warning in 2009

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.