Alert archive / Pennsylvania / Flash Flood Warnings in 1999

Flash Flood Warning 29, NWS Philadelphia/Mount Holly

September 5, 1999Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Sep 5, 1999, 11:34 PM EDT for Chester County, Pennsylvania. It was in force for 14 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
Sep 5, 1999, 11:34 PM EDT (03:34 UTC)
Expired
Sep 6, 1999, 2:00 PM EDT
In force
14 hr
Issued by
NWS Philadelphia/Mount Holly
Area
Whole counties

County Chester County, PA

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 3.6 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 1999-09-06Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 172 joules per kilogram.LCLLFCEL10008507005003002001001 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 1999-09-06The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 85 square meters per square second.1939Sfc1 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
172 J/kg
Mixed-layer CIN
-2 J/kg
Mixed-layer LCL
969 m above ground
0-6 km bulk shear
26 kt
0-1 km storm-relative helicity
85 m²/s²
0-3 km storm-relative helicity
105 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.7

Open this sounding in Storm Lab

The text

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

000 
TTAA00 KPHI 060418 COR
FFWPHL
PAC029-060600-

FLOOD WARNING - CORRECTION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1134 PM EDT SUN SEP 5 1999

A FLOOD WARNING HAS BEEN ISSUED FOR CHESTER COUNTY IN PENNSYLVANIA. 

SMALL STREAM LEVELS CONTINUE TO RISE TONIGHT AS RAINFALL OF 1.5 TO
2.5 INCHES OF RAIN HAS FALLEN OVER THE PAST SEVERAL HOURS.
AT 1133 PM THE STAGE AT VALLEY CREEK IN VALLEY FORGE WAS 6.72 FEET 
AND RISING. FLOOD STAGE IS 7.0 FEET AND THIS WILL BE EXCEEDED WITHIN 
THE NEXT HOUR.

DO NOT DRIVE THROUGH FLOODED AREAS...THE WATER MAY BE DEEPER THAN   
YOU THINK.

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.

FOR THE LATEST STORM INFORMATION...PLEASE TUNE TO NOAA WEATHER   
RADIO...YOUR LOCAL RADIO OR TELEVISION STATIONS...OR YOUR CABLE   
TELEVISION OUTLET.

NPC/TG

$$
COR FOR FIP CODE

Nearby

Flash Flood Warnings in Pennsylvania, 1999Every flash flood warning in 1999

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.