Alert archive / Pennsylvania / Flash Flood Warnings in 2007

Flash Flood Warning 19, NWS Philadelphia/Mount Holly

June 11, 2007Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Jun 11, 2007, 3:39 AM EDT for Chester County, Pennsylvania. It was in force for 3 hr. 1 report came from inside the area while it was in force.

The area

The counties it named, with what was reported inside it.

The facts

Issued: Jun 11, 2007, 3:39 AM EDT (07:39 UTC)
Expired: Jun 11, 2007, 6:30 AM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Whole counties

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 114 km from the middle of the area, began a volume at 07:40 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
Jun 11, 4:40 AM EDT	FLASH FLOOD	3 Sw Downingtown, PA	FLOODING ON BROAD RUN ROAD IN WEST BRADFORD TOWNSHIP.

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 00:00Z, 7.7 hours before the alert went out and 182 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: 849 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 1034 m above ground
0-6 km bulk shear: 37 kt
0-1 km storm-relative helicity: 65 m²/s²
0-3 km storm-relative helicity: 66 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.3

Open this sounding in Storm Lab

The text

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

000 
WGUS51 KPHI 110739
FFWPHI
PAC029-111030-

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
340 AM EDT MON JUN 11 2007

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  CENTRAL CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...

* UNTIL 630 AM EDT

* AT 335 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  THAT 2 TO 3 INCHES OF RAIN HAD FALLEN IN PARTS OF CENTRAL
  CHESTER COUNTY SINCE 2:00 AM.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO 
  THORNDALE...DOWNINGTOWN AND COATESVILLE.

ADDITIONAL RAINFALL AMOUNTS OF ONE TO TWO INCHES ARE POSSIBLE BEFORE 
4:30 AM, AS A NEARLY STATIONARY THUNDERSTORM REMAINS OVER THE REGION.
THE THUNDERSTORMS SHOULD BEGIN TO DISSIPATE AROUND THAT TIME. 

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE 
DANGERS OF FLOODING.  IF FLASH FLOODING IS OBSERVED ACT QUICKLY. 
MOVE UP TO HIGHER GROUND TO ESCAPE FLOOD WATERS.  DO NOT STAY IN 
AREAS SUBJECT TO FLOODING WHEN WATER BEGINS RISING.

LAT...LON 3988 7587 3988 7564 4006 7564 4006 7588

$$

IOVINO

2 follow-up statements

000 
WGUS71 KPHI 110840
FFSPHI

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
440 AM EDT MON JUN 11 2007

PAC029-111030-
CHESTER PA-
440 AM EDT MON JUN 11 2007

...A FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 630 AM EDT FOR
CENTRAL CHESTER COUNTY...

AT 435 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO 
INDICATE A THUNDERSTORM OVER CENTRAL CHESTER COUNTY.  THE 
THUNDERSTORM WAS BEGINNING TO WEAKEN AND DRIFT TO THE SOUTH.

THE THUNDERSTORM HAD REMAINED NEARLY STATIONARY SINCE IT DEVELOPED 
OVER CENTRAL CHESTER COUNTY AROUND 2:00 AM.  RADAR ESTIMATES 
INDICATE THAT UP TO FOUR INCHES OF RAIN MAY HAVEN FALLEN AROUND 
THORNDALE.

EVEN THOUGH RAINFALL RATES HAVE BEGUN TO DECREASE, RUNOFF FROM THE 
HEAVY RAIN WILL CONTINUE TO RESULT IN FLOODING UNTIL SHORTLY AFTER 
DAYBREAK. 

LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO 
THORNDALE...DOWNINGTOWN AND COATESVILLE

LAT...LON 3988 7587 3988 7564 4006 7564 4006 7588

$$

IOVINO

000 
WGUS71 KPHI 111024
FFSPHI

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
625 AM EDT MON JUN 11 2007

PAC029-111035-
CHESTER PA-
625 AM EDT MON JUN 11 2007

...THE FLASH FLOOD WARNING WILL EXPIRE AT 630 AM EDT FOR CENTRAL
CHESTER COUNTY...

THE HEAVY RAIN HAS DISSIPATED AND MOVED OUT OF CENTRAL CHESTER 
COUNTY.  AS A RESULT, THE FLASH FLOOD WARNING WILL BE ALLOWED TO 
EXPIRE.

A NEARLY STATIONARY THUNDERSTORM DUMPED TWO TO FOUR INCHES OF RAIN 
IN CENTRAL CHESTER COUNTY BETWEEN 2:00 AND 4:30 AM.  THE HEAVY RAIN 
RESULTED IN ROADWAY FLOODING.

LAT...LON 3988 7587 3988 7564 4006 7564 4006 7588

$$

IOVINO

The office that day

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

Issued	Product	Office	Counties	Lasted
Jun 11, 4:42 PM EDT	Severe Thunderstorm Warning	PHI	Montgomery	33 min
Jun 11, 5:08 PM EDT	Severe Thunderstorm Warning	PHI	Delaware	37 min

Nearby

Flash Flood Warnings in Pennsylvania, 2007 Every flash flood warning in 2007

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.