Alert archive / Pennsylvania / Flash Flood Warnings in 1998

Flash Flood Warning 10, NWS Philadelphia/Mount Holly

April 1, 1998Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Apr 1, 1998, 8:10 PM EST for Chester County, Montgomery County, Pennsylvania. It was in force for 110 min. 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 1, 1998, 8:10 PM EST (01:10 UTC)
Expired
Apr 1, 1998, 10:00 PM EST
In force
110 min
Issued by
NWS Philadelphia/Mount Holly
Area
Whole counties

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 99 km from the middle of the area, began a volume at 01:13 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, 1.2 hours before the alert went out and 203 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 1998-04-02Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1170 joules per kilogram.LCLEL10008507005003002001001 km2 km3 km6 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 1998-04-02The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 104 square meters per square second.1939587897Sfc1 km3 km6 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
1170 J/kg
Mixed-layer CIN
-6 J/kg
Mixed-layer LCL
817 m above ground
0-6 km bulk shear
80 kt
0-1 km storm-relative helicity
104 m²/s²
0-3 km storm-relative helicity
192 m²/s²
Significant tornado parameter
0.6
Supercell composite
3.7

Open this sounding in Storm Lab

The text

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

000 
TTAA00 KPHL 020109
FFWPHL
PAC029-091-020300-

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
810 PM EST WED APR 1 1998

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS EXPANDED THE
FLASH FLOOD WARNING EFFECTIVE UNTIL 1000 PM EST
FOR PEOPLE IN THE FOLLOWING LOCATIONS...

IN PENNSYLVANIA

   ...ALL OF CHESTER COUNTY
   ...SOUTHEASTERN AND CENTRAL MONTGOMERY COUNTY

NATIONAL WEATHER SERVICE RADAR INDICATED UPWARDS OF 3 INCHES OF
RAIN HAD FALLEN ACROSS PARTS OF MONTGOMERY AND CHESTER COUNTY LATE
THIS AFTERNOON. MORE RAIN IS POSSIBLE THIS EVENING AS ADDITIONAL
THUNDERSTORMS WILL MOVE THROUGH THE REGION.

THE VALLEY CREEK AT VALLEY FORGE HAD REACHED 7.4 FEET AS OF 8
PM...THE ESTIMATED FLOOD STAGE THERE IS 7 FEET. THE BRANDYWINE CREEK
AT DOWNINGTOWN HAD REACHED A STAGE OF 6.96 FEET...FLOOD STAGE THERE
IS 7 FEET.

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

KRAUS

The office that day

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

IssuedProductOfficeCountiesLasted
Apr 1, 9:25 PM ESTSevere Thunderstorm WarningPHIBucks50 min
Apr 1, 9:43 PM ESTSevere Thunderstorm WarningPHIChester32 min
Apr 1, 9:56 PM ESTFlash Flood WarningPHIChester, Montgomery2 hr
Apr 2, 12:30 AM ESTFlash Flood WarningPHIBucks3 hr

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.