Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2011

Severe Thunderstorm Warning 297, NWS Philadelphia/Mount Holly

September 11, 2011Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Sep 11, 2011, 9:24 PM EDT for Chester County, Pennsylvania. It was in force for 51 min. 4 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: Sep 11, 2011, 9:24 PM EDT (01:24 UTC)
Expired: Sep 11, 2011, 10:15 PM EDT
In force: 51 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 119 km from the middle of the area, began a volume at 01:27 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
Sep 11, 9:30 PM EDT	TSTM WND DMG	West Brandywine Twp, PA	TREES DOWN.
Sep 11, 9:35 PM EDT	HAIL 1	Coatesville, PA
Sep 11, 9:40 PM EDT	HAIL 1	2 E Wagontown, PA
Sep 11, 9:55 PM EDT	HAIL 1.25	Downingtown, PA

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, 1.4 hours before the alert went out and 188 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: 420 J/kg
Mixed-layer CIN: -58 J/kg
Mixed-layer LCL: 1369 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 144 m²/s²
0-3 km storm-relative helicity: 126 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.

560 
WUUS51 KPHI 120124
SVRPHI
PAC029-120215-
/O.NEW.KPHI.SV.W.0297.110912T0124Z-110912T0215Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
924 PM EDT SUN SEP 11 2011

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  CENTRAL CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...
  THIS INCLUDES THE CITY OF WEST CHESTER...

* UNTIL 1015 PM EDT

* AT 920 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN EXCESS
  OF 60 MPH.  THIS STORM WAS LOCATED NEAR HONEY BROOK...OR 14 MILES
  NORTHWEST OF WEST CHESTER...AND MOVING EAST AT 15 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
  GLENMOORE AROUND 935 PM EDT...
  DOWNINGTOWN AROUND 950 PM EDT...
  7 MILES NORTH OF MARSHALLTON AND 8 MILES SOUTH OF PUGHTOWN AROUND
  955 PM EDT...
  LIONVILLE AROUND 1000 PM EDT...
  CHESTER SPRINGS AND 6 MILES NORTH OF WEST CHESTER AROUND 1005 PM
  EDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO DAMAGING WINDS...CONTINUOUS CLOUD TO GROUND 
LIGHTNING IS OCCURRING WITH THIS STORM. MOVE INDOORS IMMEDIATELY! 
LIGHTNING IS ONE OF NATURES GREATEST KILLERS. REMEMBER...IF YOU CAN 
HEAR THUNDER...YOU ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.

PLEASE REPORT HAIL OR STRONG WINDS TO THE NATIONAL WEATHER SERVICE BY
CALLING TOLL FREE...1-877-633-6772...WHEN YOU CAN DO SO SAFELY.

&&

LAT...LON 4011 7595 4013 7592 4016 7585 4021 7560
      4017 7556 3993 7558 3996 7596
TIME...MOT...LOC 0124Z 273DEG 15KT 4005 7583

$$

MPD

1 follow-up statement

996 
WWUS51 KPHI 120151
SVSPHI

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
951 PM EDT SUN SEP 11 2011

PAC029-120215-
/O.CON.KPHI.SV.W.0297.000000T0000Z-110912T0215Z/
CHESTER PA-
951 PM EDT SUN SEP 11 2011

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1015 PM EDT
FOR CENTRAL CHESTER COUNTY...

AT 948 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN
EXCESS OF 60 MPH.  THIS STORM WAS LOCATED NEAR DOWNINGTOWN...OR 7
MILES NORTHWEST OF WEST CHESTER...MOVING EAST AT 20 MPH.

THE SEVERE THUNDERSTORM WILL BE NEAR...
  LIONVILLE AND MARSHALLTON BY 955 PM EDT...
  EXTON AND 6 MILES SOUTH OF CHESTER SPRINGS BY 1000 PM EDT...
  WEST CHESTER BY 1005 PM EDT...

ANOTHER STORM WAS APPROACHING CHESTER COUNTY FROM THE WEST. ALTHOUGH 
IT DID NOT APPEAR SEVERE...IT HAS THE POTENTIAL TO STRENGTHEN. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO DAMAGING WINDS...DANGEROUS CLOUD TO GROUND LIGHTNING 
IS OCCURRING WITH THE MAIN STORM. MOVE INDOORS IMMEDIATELY! 
LIGHTNING IS ONE OF NATURES NUMBER ONE KILLERS. REMEMBER...IF YOU 
CAN HEAR THUNDER...YOU ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.

PLEASE REPORT HAIL OR STRONG WINDS TO THE NATIONAL WEATHER SERVICE BY
CALLING TOLL FREE...1-877-633-6772...WHEN YOU CAN DO SO SAFELY.

&&

LAT...LON 4011 7595 4013 7592 4016 7585 4021 7560
      4017 7556 3993 7558 3996 7596
TIME...MOT...LOC 0149Z 283DEG 16KT 4002 7570

$$

MPD

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 11, 8:19 PM EDT	Flash Flood Warning	PHI	Berks	3 hr
Sep 11, 8:46 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Sep 11, 9:00 PM EDT	Flash Flood Warning	PHI	Chester	3 hr
Sep 11, 9:14 PM EDT	Flash Flood Warning	PHI	Berks, Chester, Montgomery	110 min
Sep 11, 9:14 PM EDT	Special Weather Statement	PHI	Berks, Chester, Lehigh, Montgomery	61 min
Sep 11, 9:34 PM EDT	Special Weather Statement	PHI	Philadelphia	41 min
Sep 11, 9:54 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery	51 min
Sep 11, 9:56 PM EDT	Flash Flood Warning	PHI	Bucks, Chester, Delaware, Montgomery, Philadelphia	4 hr
Sep 11, 10:25 PM EDT	Special Weather Statement	PHI	Philadelphia	65 min
Sep 11, 10:29 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	46 min
Sep 11, 10:44 PM EDT	Areal Flood Advisory	PHI	Chester	107 min
Sep 11, 10:52 PM EDT	Special Weather Statement	PHI	Bucks, Delaware, Montgomery, Philadelphia	83 min
Sep 11, 11:10 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Philadelphia	65 min
Sep 12, 11:05 AM EDT	Coastal Flood Statement	PHI	Delaware, Philadelphia	6 hr

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2011 Every severe thunderstorm warning in 2011

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.