Alert archive / Pennsylvania / Flash Flood Warnings in 2008

Flash Flood Warning 4, NWS Philadelphia/Mount Holly

March 20, 2008Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Mar 20, 2008, 1:17 AM EDT for Chester County, Pennsylvania. It was in force for 118 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Mar 20, 2008, 1:17 AM EDT (05:17 UTC)
Expired: Mar 20, 2008, 3:15 AM EDT
In force: 118 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 117 km from the middle of the area, began a volume at 05:19 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, 5.3 hours before the alert went out and 194 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 711 m above ground
0-6 km bulk shear: 64 kt
0-1 km storm-relative helicity: 576 m²/s²
0-3 km storm-relative helicity: 815 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 
WGUS51 KPHI 200524
FFWPHI
PAC029-200715-
/O.NEW.KPHI.FF.W.0004.080320T0517Z-080320T0715Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
117 AM EDT THU MAR 20 2008

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

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

* UNTIL 315 AM EDT

* AT 110 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED   
  VERY HEAVY RAIN FROM A LINE OF SHOWERS THAT WAS TRAINING OVER THE 
  WARNED AREA.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO            
  CEDARVILLE...PUGHTOWN AND ELVERSON.

OVER AN INCH OF RAIN HAS FALLEN IN THE PAST HOUR. ADDITIONAL 
RAINFALL AMOUNTS UP TO ONE-HALF INCH IS POSSIBLE IN THE WARNED AREA. 
NEARLY SATURATED SOILS FROM PREVIOUS RAINS ARE EXACERBATING THE 
FLOOD POTENTIAL.

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.

A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING. 
DO NOT ATTEMPT TO CROSS SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN 
DEPTH BY FOOT OR BY AUTOMOBILE.

LAT...LON 4003 7597 4004 7595 4011 7595 4022 7573
      4025 7569 4025 7567 4022 7562 4023 7561
      4020 7558 4020 7556 4015 7554 3996 7599
TIME...MOT...LOC 0517Z 180DEG 0KT 4010 7584

$$

KRUZDLO

The office that day

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

Issued	Product	Office	Counties	Lasted
Mar 20, 1:36 AM EDT	Flash Flood Warning	PHI	Bucks, Montgomery	2 hr
Mar 20, 2:59 AM EDT	Wind Advisory	PHI	Berks, Carbon, Delaware, Lehigh, Monroe, Northampton and 1 more	36 hr

Nearby

Flash Flood Warnings in Pennsylvania, 2008 Every flash flood warning in 2008

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.