Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2011

Severe Thunderstorm Warning 35, NWS Philadelphia/Mount Holly

April 28, 20114 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Apr 28, 2011, 12:11 PM EDT for 4 counties in Pennsylvania. It was in force for 31 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: Apr 28, 2011, 12:11 PM EDT (16:11 UTC)
Expired: Apr 28, 2011, 12:42 PM EDT
In force: 31 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon

Counties Bucks County, PA, Chester County, PA, Delaware County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 81 km from the middle of the area, began a volume at 16:11 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 watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
Apr 28, 9:45 AM EDT	Severe Thunderstorm Watch	SPC	6 hr

The nearest sounding before it

Phillips Aaf/Abe, MD (KAPG), launched 12:00Z, 4.2 hours before the alert went out and 112 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: 482 J/kg
Mixed-layer CIN: -47 J/kg
Mixed-layer LCL: 670 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 371 m²/s²
0-3 km storm-relative helicity: 401 m²/s²
Significant tornado parameter: 1.3
Supercell composite: 5.5

Open this sounding in Storm Lab

The text

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

668 
WUUS51 KPHI 281611
SVRPHI
PAC017-029-045-091-281715-
/O.NEW.KPHI.SV.W.0035.110428T1611Z-110428T1715Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1211 PM EDT THU APR 28 2011

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  CENTRAL BUCKS COUNTY IN SOUTHEAST PENNSYLVANIA...
  NORTHEASTERN CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...
  NORTH CENTRAL DELAWARE COUNTY IN SOUTHEAST PENNSYLVANIA...
  MONTGOMERY COUNTY IN SOUTHEAST PENNSYLVANIA...

* UNTIL 115 PM EDT

* AT 1208 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND   
  DAMAGING WINDS TO 60 MPH.  THIS STORM WAS LOCATED NEAR             
  VALLEY FORGE...OR 9 MILES NORTHEAST OF WEST CHESTER...AND          
  MOVING NORTHEAST AT 55 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
  COLLEGEVILLE...TRAPPE AND NORRISTOWN AROUND 1215 PM EDT...
  LANSDALE...HATFIELD AND SOUDERTON AROUND 1220 PM EDT...
  CHALFONT AND FRICKS AROUND 1225 PM EDT...
  ROBESONIA AND GARDENVILLE AROUND 1230 PM EDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THIS IS A DANGEROUS STORM. IF YOU ARE IN ITS PATH...PREPARE 
IMMEDIATELY FOR DAMAGING WINDS...LARGE HAIL...AND DEADLY CLOUD TO 
GROUND LIGHTNING. PEOPLE OUTSIDE SHOULD MOVE TO A 
SHELTER...PREFERABLY INSIDE A STRONG BUILDING BUT AWAY FROM WINDOWS.

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.

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 400 PM EDT
THURSDAY AFTERNOON FOR DELAWARE AND NORTHEASTERN MARYLAND AND NEW
JERSEY AND EASTERN PENNSYLVANIA.

&&

LAT...LON 4053 7519 4021 7482 4009 7524 3994 7558
      4021 7567
TIME...MOT...LOC 1610Z 228DEG 48KT 4012 7547

$$

GORSE

2 follow-up statements

631 
WWUS51 KPHI 281629
SVSPHI

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1229 PM EDT THU APR 28 2011

PAC029-045-281638-
/O.CAN.KPHI.SV.W.0035.000000T0000Z-110428T1715Z/
DELAWARE PA-CHESTER PA-
1229 PM EDT THU APR 28 2011

...THE SEVERE THUNDERSTORM WARNING FOR NORTHEASTERN CHESTER AND NORTH
CENTRAL DELAWARE COUNTIES IS CANCELLED...

THE THUNDERSTORM THAT PROMPTED THE WARNING HAS EXITED THE AREA, 
THEREFORE THE WARNING HAS BEEN CANCELLED.

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 400 PM EDT
THURSDAY AFTERNOON FOR DELAWARE AND NORTHEASTERN MARYLAND AND NEW
JERSEY AND EASTERN PENNSYLVANIA.

LAT...LON 4007 7530 4033 7548 4053 7519 4021 7482
      4009 7524
TIME...MOT...LOC 1628Z 228DEG 48KT 4029 7519

$$

PAC017-091-281715-
/O.CON.KPHI.SV.W.0035.000000T0000Z-110428T1715Z/
MONTGOMERY PA-BUCKS PA-
1229 PM EDT THU APR 28 2011

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 115 PM EDT
FOR CENTRAL BUCKS AND EASTERN MONTGOMERY COUNTIES...

AT 1226 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO 
INDICATE A SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS 
TO 60 MPH. THIS STORM WAS LOCATED NEAR MONTGOMERYVILLE...OR 18 MILES 
NORTH OF PHILADELPHIA...MOVING NORTHEAST AT 55 MPH.

THE SEVERE THUNDERSTORM WILL BE NEAR...
  ROBESONIA...GARDENVILLE...PIPERSVILLE AND 6 MILES SOUTHEAST OF
  BEDMINSTER BY 1235 PM EDT...
  TINICUM TOWNSHIP AND 8 MILES SOUTHEAST OF OTTSVILLE BY 1240 PM
  EDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THIS IS A DANGEROUS STORM. IF YOU ARE IN ITS PATH...PREPARE 
IMMEDIATELY FOR DAMAGING WINDS AND DEADLY CLOUD TO GROUND LIGHTNING. 
PEOPLE OUTSIDE SHOULD MOVE TO A SHELTER...PREFERABLY INSIDE A STRONG 
BUILDING BUT AWAY FROM WINDOWS.

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 400 PM EDT
THURSDAY AFTERNOON FOR DELAWARE AND NORTHEASTERN MARYLAND AND NEW
JERSEY AND EASTERN PENNSYLVANIA.

&&

LAT...LON 4007 7530 4033 7548 4053 7519 4021 7482
      4009 7524
TIME...MOT...LOC 1628Z 228DEG 48KT 4029 7519

$$

GORSE

944 
WWUS51 KPHI 281642
SVSPHI

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1242 PM EDT THU APR 28 2011

PAC017-091-281651-
/O.CAN.KPHI.SV.W.0035.000000T0000Z-110428T1715Z/
MONTGOMERY PA-BUCKS PA-
1242 PM EDT THU APR 28 2011

...THE SEVERE THUNDERSTORM WARNING FOR CENTRAL BUCKS AND EASTERN
MONTGOMERY COUNTIES IS CANCELLED...

THE THUNDERSTORM HAS WEAKENED AND ARE SHIFTING NORTHEAST OF THE 
AREA, THEREFORE THE WARNING HAS BEEN CANCELLED.

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 400 PM EDT
THURSDAY AFTERNOON FOR DELAWARE AND NORTHEASTERN MARYLAND AND NEW
JERSEY AND EASTERN PENNSYLVANIA.

LAT...LON 4007 7530 4033 7548 4053 7519 4021 7482
      4009 7524
TIME...MOT...LOC 1641Z 228DEG 48KT 4041 7502

$$

GORSE

The office that day

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

Issued	Product	Office	Counties	Lasted
Apr 28, 4:24 AM EDT	Special Weather Statement	PHI	Berks, Carbon, Lehigh, Northampton	66 min
Apr 28, 4:36 AM EDT	Severe Thunderstorm Warning	PHI	Berks, Carbon, Lehigh, Monroe, Northampton	54 min
Apr 28, 5:31 AM EDT	Special Weather Statement	PHI	Carbon, Monroe	59 min
Apr 28, 5:49 AM EDT	Special Weather Statement	PHI	Carbon	56 min
Apr 28, 5:58 AM EDT	Areal Flood Advisory	PHI	Berks, Carbon, Lehigh, Monroe, Northampton	3 hr
Apr 28, 6:12 AM EDT	Special Weather Statement	PHI	Chester, Delaware, Philadelphia	63 min
Apr 28, 6:18 AM EDT	Severe Thunderstorm Warning	PHI	Carbon, Monroe	57 min
Apr 28, 6:23 AM EDT	Special Weather Statement	PHI	Berks, Chester, Lehigh, Montgomery	52 min
Apr 28, 6:56 AM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Chester, Delaware, Lehigh, Montgomery and 2 more	34 min
Apr 28, 7:06 AM EDT	Flash Flood Warning	PHI	Carbon, Monroe	6 hr
Apr 28, 7:35 AM EDT	Special Weather Statement	PHI	Bucks	55 min
Apr 28, 8:17 AM EDT	Special Weather Statement	PHI	Berks	58 min
Apr 28, 8:55 AM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh	65 min
Apr 28, 8:59 AM EDT	Areal Flood Advisory	PHI	Berks, Lehigh	4 hr
Apr 28, 9:11 AM EDT	Special Weather Statement	PHI	Carbon, Monroe	49 min
Apr 28, 9:33 AM EDT	Severe Thunderstorm Warning	PHI	Carbon, Lehigh, Monroe, Northampton	57 min
Apr 28, 10:00 AM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Chester, Lehigh, Montgomery	60 min
Apr 28, 10:25 AM EDT	Severe Thunderstorm Warning	PHI	Bucks, Carbon, Lehigh, Monroe, Northampton	50 min
Apr 28, 10:48 AM EDT	Areal Flood Advisory	PHI	Bucks, Chester, Montgomery, Northampton	3 hr
Apr 28, 10:57 AM EDT	Severe Thunderstorm Warning	PHI	Berks, Bucks, Chester, Lehigh, Montgomery, Northampton	63 min
Apr 28, 10:58 AM EDT	Tornado Warning	PHI	Bucks, Northampton	32 min
Apr 28, 11:11 AM EDT	Severe Thunderstorm Warning	PHI	Northampton	64 min
Apr 28, 12:03 PM EDT	Special Weather Statement	PHI	Montgomery, Philadelphia	57 min
Apr 28, 12:42 PM EDT	Special Weather Statement	PHI	Delaware	63 min
Apr 28, 12:45 PM EDT	Special Weather Statement	PHI	Bucks, Delaware, Montgomery, Philadelphia	60 min
Apr 28, 1:23 PM EDT	Areal Flood Advisory	PHI	Philadelphia	103 min

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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.