Alert archive / Pennsylvania / Flash Flood Warnings in 1999

Flash Flood Warning 12, NWS Philadelphia/Mount Holly

March 21, 1999Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Mar 21, 1999, 10:34 PM EST for Montgomery County, Pennsylvania. It was in force for 3 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
Mar 21, 1999, 10:34 PM EST (03:34 UTC)
Expired
Mar 22, 1999, 2:00 AM EST
In force
3 hr
Issued by
NWS Philadelphia/Mount Holly
Area
Whole counties

County Montgomery County, PA

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 3.6 hours before the alert went out and 224 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 1999-03-22Temperature 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 1999-03-22The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -185 square meters per square second.1939587897Sfc1 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
499 m above ground
0-6 km bulk shear
58 kt
0-1 km storm-relative helicity
-185 m²/s²
0-3 km storm-relative helicity
-252 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 220335
FFWPHL
PAC091-220700-

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1034 PM EST SUN MAR 21 1999

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  MONTGOMERY COUNTY IN PENNSYLVANIA.

* UNTIL 200 AM EST.

* AT 1030 PM...RADAR INDICATED RAINS OF 1 TO 1 1/2 INCHES THROUGH
  THE COUNTY WITH LOCALIZED HIGHER AMOUNTS. A SPOTTER ALSO
  REPORTED 2.34 INCHES OF RAIN IN LAFAYETTE HILL.

* FLOODING CAN BE EXPECTED ON VERY SMALL STREAMS AND IN POOR
  DRAINAGE AREAS.

  DO NOT DRIVE YOUR VEHICLE INTO AREAS WHERE THE WATER COVERS THE
  ROADWAY. THE WATER DEPTH MAY BE TOO GREAT TO ALLOW YOUR CAR TO
  CROSS SAFELY. VEHICLES CAUGHT IN RISING WATER SHOULD BE ABANDONED
  QUICKLY. MOVE TO HIGHER GROUND.

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

  .END
  RNS

The office that day

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

IssuedProductOfficeCountiesLasted
Mar 21, 7:57 PM ESTFlash Flood WarningPHIChester6 hr
Mar 21, 9:10 PM ESTFlash Flood WarningPHIBerks5 hr
Mar 21, 9:40 PM ESTFlash Flood WarningPHICarbon, Lehigh, Monroe4 hr
Mar 21, 11:15 PM ESTFlash Flood WarningPHIBucks3 hr
Mar 21, 11:50 PM ESTFlash Flood WarningPHIPhiladelphia3 hr
Mar 22, 12:19 AM ESTFlash Flood WarningPHIBucks, Delaware, Montgomery, Philadelphia3 hr
Mar 22, 12:19 AM ESTFlash Flood WarningPHICarbon, Lehigh, Monroe, Northampton3 hr
Mar 22, 12:19 AM ESTFlash Flood WarningPHIBerks, Chester3 hr

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.