Alert archive / Pennsylvania / Flash Flood Warnings in 2009

Flash Flood Warning 65, NWS Philadelphia/Mount Holly

October 24, 2009Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this flash flood warning at Oct 24, 2009, 6:02 PM EDT for Montgomery County, Pennsylvania. It was in force for 3 hr. 3 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Oct 24, 2009, 6:02 PM EDT (22:02 UTC)
Expired: Oct 24, 2009, 9:00 PM EDT
In force: 3 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

County Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 92 km from the middle of the area, began a volume at 22:03 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.

What was reported inside it

Time	Report	Where	Remark
Oct 24, 6:15 PM EDT	FLASH FLOOD	2 Wnw Conshohocken, PA	FLOODING ON THE SCHULYKILL EXPRESSWAY IN LOWER MERION TOWNSHIP.
Oct 24, 9:00 PM EDT	FLOOD	2 Ese Ambler, PA	FLOODING ALONG THE WISSAHICKON CREEK IN FORT WASHINGTON, UPPER DUBLIN TOWNSHIP.
Oct 24, 9:00 PM EDT	FLOOD	Schwenksville, PA	FLOODING ALONG THE EAST BRANCH OF THE PERKIOMEN CREEK.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 10.0 hours before the alert went out and 215 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: 288 J/kg
Mixed-layer CIN: -16 J/kg
Mixed-layer LCL: 586 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 309 m²/s²
0-3 km storm-relative helicity: 369 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 2.7

Open this sounding in Storm Lab

The text

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

000 
WGUS51 KPHI 242202
FFWPHI
PAC091-250100-
/O.NEW.KPHI.FF.W.0065.091024T2202Z-091025T0100Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
602 PM EDT SAT OCT 24 2009

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

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

* UNTIL 900 PM EDT

* AT 600 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  FLASH FLOODING FROM A THUNDERSTORM OVER THE WARNED AREA.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO TRAPPE...
  SPRING MOUNT...SCHWENKSVILLE...ROYERSFORD...PLYMOUTH MEETING...
  NORRISTOWN...LANSDALE...HATFIELD...GREEN LANE...COLLEGEVILLE AND
  AMBLER

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. ADDITIONALLY...COUNTRY
ROADS AND FARMLANDS ALONG THE BANKS OF CREEKS...STREAMS AND OTHER LOW
LYING AREAS ARE SUBJECT TO FLOODING.

A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING.
IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY.
RESIDENTS LIVING ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE
PRECAUTIONS TO PROTECT LIFE AND PROPERTY. DO NOT ATTEMPT TO CROSS
SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN DEPTH BY FOOT OR BY
AUTOMOBILE.

&&

LAT...LON 4004 7529 4014 7551 4016 7551 4015 7553
      4016 7554 4020 7556 4020 7559 4022 7559
      4038 7544 4017 7510

$$

RNS

The office that day

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

Issued	Product	Office	Counties	Lasted
Oct 24, 3:30 PM EDT	Areal Flood Advisory	PHI	Berks, Carbon, Chester, Lehigh, Monroe, Northampton	4 hr
Oct 24, 4:49 PM EDT	Areal Flood Advisory	PHI	Bucks, Delaware, Montgomery, Northampton, Philadelphia	4 hr
Oct 24, 4:55 PM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery	4 hr
Oct 24, 5:41 PM EDT	Flash Flood Warning	PHI	Chester, Delaware	3 hr
Oct 24, 6:28 PM EDT	Severe Thunderstorm Warning	PHI	Bucks	47 min

Nearby

Flash Flood Warnings in Pennsylvania, 2009 Every flash flood warning in 2009

Sources

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