Alert archive / Pennsylvania / Areal Flood Warnings in 2012

Areal Flood Warning 3, NWS Philadelphia/Mount Holly

May 15, 2012Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this areal flood warning at May 15, 2012, 11:38 PM EDT for Chester County, Montgomery County, Pennsylvania. It was in force for 4 hr. 2 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: May 15, 2012, 11:38 PM EDT (03:38 UTC)
Expired: May 16, 2012, 3:46 AM EDT
In force: 4 hr
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Flood severity: None

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 98 km from the middle of the area, began a volume at 03:41 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
May 16, 12:41 AM EDT	FLASH FLOOD	Upper Merion Twp, PA	FLASH FLOODING ALONG S. GULF ROAD AS THE GULF CREEK OVERFLOWED ITS BANKS.
May 16, 1:15 AM EDT	FLASH FLOOD	Tredyffrin Twp, PA	EIGHT WATER RESCUES PERFORMED IN TREDYFFRIN AND EASTTOWN TWPS AS THE VALLEY AND DARBY CREEKS OVERFLOWED THEIR BANKS.

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 00:00Z, 3.6 hours before the alert went out and 210 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: 401 J/kg
Mixed-layer CIN: -9 J/kg
Mixed-layer LCL: 1311 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 5 m²/s²
0-3 km storm-relative helicity: 58 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

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

451 
WGUS41 KPHI 160338
FLWPHI

BULLETIN - IMMEDIATE BROADCAST REQUESTED
FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1138 PM EDT TUE MAY 15 2012

PAC029-091-160630-
/O.NEW.KPHI.FA.W.0003.120516T0338Z-120516T0630Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY PA-CHESTER PA-
1138 PM EDT TUE MAY 15 2012

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* FLOOD WARNING FOR URBAN AREAS AND SMALL STREAMS IN...
  CENTRAL MONTGOMERY COUNTY IN SOUTHEAST PENNSYLVANIA...
  NORTHEASTERN CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...

* UNTIL 230 AM EDT

* AT 1135 PM EDT A SERIES OF THUNDERSTORMS ARE MOVING ACROSS CHESTER 
AND MONTGOMERY COUNTIES PRODUCING RAINFALL TOTALS UPWARDS OF 2 
INCHES IN ONE HOUR. THE HEAVY RAINFALL WILL CAUSE URBAN AND SMALL 
STREAM FLOODING OVER THE NEXT COUPLE OF HOURS.

A FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR HAS BEEN REPORTED.
STREAM RISES WILL BE SLOW AND FLASH FLOODING IS NOT EXPECTED.
HOWEVER...ALL INTERESTED PARTIES SHOULD TAKE NECESSARY PRECAUTIONS
IMMEDIATELY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE
DANGERS OF FLOODING. IF 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.

DO NOT UNDERESTIMATE THE POWER OF FLOOD WATERS. ONLY A FEW INCHES OF
RAPIDLY FLOWING WATER CAN QUICKLY CARRY AWAY YOUR VEHICLE.

&&

LAT...LON 4020 7577 4025 7556 4030 7538 4022 7526
      4008 7530 4005 7546 4003 7569

$$

HEAVENER

2 follow-up statements

158 
WGUS41 KPHI 160558
FLWPHI

BULLETIN - IMMEDIATE BROADCAST REQUESTED
FLOOD WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
158 AM EDT WED MAY 16 2012

PAC029-091-160930-
/O.EXT.KPHI.FA.W.0003.000000T0000Z-120516T0930Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY PA-CHESTER PA-
158 AM EDT WED MAY 16 2012

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS EXTENDED THE

* FLOOD WARNING FOR URBAN AREAS AND SMALL STREAMS IN...
  SOUTHWESTERN MONTGOMERY COUNTY IN SOUTHEAST PENNSYLVANIA...
  NORTHEASTERN CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...

* UNTIL 530 AM EDT

* AT 157 AM EDT...THE VALLEY CREEK IN VALLEY FORGE WAS IN 
FLOOD...AND MANY OTHER SMALL RIVERS...CREEKS AND STREAMS WERE NEAR 
OR OVER BANKFULL. WHILE THE HEAVIEST RAIN HAS MOVED OUT OF THE 
AREA...RUNOFF FROM THE EARLIER HEAVY RAIN COULD RESULT IN ADDITIONAL 
FLOODING...OR EXACERBATION OF THE CURRENT FLOODING.

A FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR HAS BEEN REPORTED.
STREAM RISES WILL BE SLOW AND FLASH FLOODING IS NOT EXPECTED.
HOWEVER...ALL INTERESTED PARTIES SHOULD TAKE NECESSARY PRECAUTIONS
IMMEDIATELY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE
DANGERS OF FLOODING. IF 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.

DO NOT UNDERESTIMATE THE POWER OF FLOOD WATERS. ONLY A FEW INCHES OF
RAPIDLY FLOWING WATER CAN QUICKLY CARRY AWAY YOUR VEHICLE.

&&

LAT...LON 4020 7577 4025 7556 4030 7538 4022 7526
      4008 7530 4005 7546 4003 7569

$$

HAYES

908 
WGUS81 KPHI 160746
FLSPHI

FLOOD STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
346 AM EDT WED MAY 16 2012

PAC029-091-160756-
/O.CAN.KPHI.FA.W.0003.000000T0000Z-120516T0930Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY PA-CHESTER PA-
346 AM EDT WED MAY 16 2012

...THE FLOOD WARNING HAS BEEN CANCELLED FOR URBAN AREAS AND SMALL
STREAMS IN NORTHEASTERN CHESTER AND SOUTHWESTERN MONTGOMERY
COUNTIES...

HEAVY RAIN HAS EXITED THE AREA...AND STREAMS AND CREEK HAVE DROPPED 
BELOW FLOOD STAGE AND CONTINUE TO FALL.

LAT...LON 4020 7577 4025 7556 4030 7538 4022 7526
      4008 7530 4005 7546 4003 7569

$$

HAYES

The office that day

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

Issued	Product	Office	Counties	Lasted
May 15, 8:19 PM EDT	Special Weather Statement	PHI	Bucks	86 min
May 15, 8:46 PM EDT	Areal Flood Warning	PHI	Northampton	76 min
May 15, 9:00 PM EDT	Special Weather Statement	PHI	Berks	90 min
May 15, 9:49 PM EDT	Special Weather Statement	PHI	Berks, Bucks, Chester, Lehigh, Montgomery	86 min
May 15, 10:45 PM EDT	Areal Flood Advisory	PHI	Chester	57 min
May 15, 11:05 PM EDT	Special Weather Statement	PHI	Bucks, Chester, Delaware, Montgomery	55 min
May 15, 11:24 PM EDT	Areal Flood Advisory	PHI	Chester, Montgomery	116 min
May 16, 12:12 AM EDT	Areal Flood Advisory	PHI	Chester, Delaware, Montgomery	3 hr
May 16, 12:20 AM EDT	Special Weather Statement	PHI	Delaware, Philadelphia	55 min
May 16, 12:34 AM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery	4 hr
May 16, 2:37 AM EDT	Areal Flood Warning	PHI	Philadelphia	3 hr
May 16, 4:27 AM EDT	Areal Flood Warning	PHI	Delaware	3 hr

Nearby

Areal Flood Warnings in Pennsylvania, 2012 Every areal flood warning in 2012

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.