Alert archive / Pennsylvania / Flash Flood Warnings in 1998

Flash Flood Warning 13, NWS Philadelphia/Mount Holly

April 9, 1998Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Apr 9, 1998, 8:25 PM EDT for Chester County, Pennsylvania. It was in force for 5 hr. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued
Apr 9, 1998, 8:25 PM EDT (00:25 UTC)
Expired
Apr 10, 1998, 1:00 AM EDT
In force
5 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 00:28 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.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 0.4 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-pSkew-T log-p diagram, Washington/Dulle, VA at 00:00Z on 1998-04-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 00:00Z on 1998-04-10The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -162 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
809 m above ground
0-6 km bulk shear
47 kt
0-1 km storm-relative helicity
-162 m²/s²
0-3 km storm-relative helicity
-130 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

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

000 
TTAA00 KPHL 092329
FFWPHL
PAC029-100400-

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
725 PM EST THU APR 9 1998

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A FLASH 
FLOOD WARNING EFFECTIVE UNTIL MIDNIGHT TONIGHT FOR PEOPLE IN 
THE FOLLOWING LOCATION...

IN PENNSYLVANIA

   ...CHESTER COUNTY

NATIONAL WEATHER SERVICE RADAR INDICATED ONE TO ONE AND ONE HALF
INCHES OF RAIN HAD FALLEN ACROSS NORTHEASTERN AND CENTRAL PORTIONS
OF CHESTER COUNTY.  THIS IS CAUSING THE VALLEY CREEK IN VALLEY FORGE
TO RISE RAPIDLY.  AT 701 PM EDT...THE READING FOR THE VALLEY CREEK
WAS 6.69 FEET.  THE ESTIMATED FLOOD STAGE IS 7 FEET.

THE ESTIMATED FLOOD STAGE IS 7 FEET AND THE EXPECTED CREST WILL BE 
BETWEEN 7.5 AND 8 FEET BETWEEN 10 PM AND 11 PM THIS EVENING.

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

JWH

Nearby

Flash Flood Warnings in Pennsylvania, 1998Every flash flood warning in 1998

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.