Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2009

Severe Thunderstorm Warning 204, NWS Philadelphia/Mount Holly

August 18, 20094 counties in New Jersey; 5 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 18, 2009, 7:37 PM EDT for 4 counties in New Jersey; 5 counties in Pennsylvania. It was in force for 68 min. 6 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: Aug 18, 2009, 7:37 PM EDT (23:37 UTC)
Expired: Aug 18, 2009, 8:45 PM EDT
In force: 68 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon

Counties Burlington County, NJ, Camden County, NJ, Gloucester County, NJ, Salem County, NJ, Bucks County, PA, Chester County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 68 km from the middle of the area, began a volume at 23:39 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
Aug 18, 7:44 PM EDT	TSTM WND GST 45	Philadelphia Internatio, PA
Aug 18, 7:56 PM EDT	TSTM WND GST 59	Skippack, PA	PENNY SIZE HAIL ALSO REPORTED.
Aug 18, 7:56 PM EDT	HAIL 0.75	Skippack, PA	PENNY SIZE HAIL REPORTED.
Aug 18, 8:05 PM EDT	TSTM WND DMG	Blackwood, NJ	WIRES DOWN.
Aug 18, 8:08 PM EDT	TSTM WND GST 49	Philadelphia, PA	A 49 MPH THUNDERSTORM WIND GUST WAS MEASURED AT THE NORTHEAST PHILADELPHIA AIRPORT.
Aug 18, 8:27 PM EDT	TSTM WND DMG	1 Se Berlin, NJ	TREES AND WIRES DOWN.

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

The nearest sounding before it

Phillips Aaf/Abe, MD (KAPG), launched 12:00Z, 11.6 hours before the alert went out and 109 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: 810 J/kg
Mixed-layer CIN: -78 J/kg
Mixed-layer LCL: 1015 m above ground
0-6 km bulk shear: 10 kt
0-1 km storm-relative helicity: 14 m²/s²
0-3 km storm-relative helicity: 20 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 
WUUS51 KPHI 182337
SVRPHI
NJC005-007-015-033-PAC017-029-045-091-101-190045-
/O.NEW.KPHI.SV.W.0204.090818T2337Z-090819T0045Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
737 PM EDT TUE AUG 18 2009

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY NJ HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  BUCKS COUNTY IN SOUTHEAST PENNSYLVANIA...
  NORTHEASTERN CHESTER COUNTY IN SOUTHEAST PENNSYLVANIA...
  EASTERN DELAWARE COUNTY IN SOUTHEAST PENNSYLVANIA...
  MONTGOMERY COUNTY IN SOUTHEAST PENNSYLVANIA...
  PHILADELPHIA COUNTY IN SOUTHEAST PENNSYLVANIA...
  THIS INCLUDES THE CITY OF PHILADELPHIA...
  NORTHWESTERN BURLINGTON COUNTY IN SOUTHERN NEW JERSEY...
  CAMDEN COUNTY IN SOUTHERN NEW JERSEY...
  THIS INCLUDES THE CITY OF CAMDEN...
  EASTERN GLOUCESTER COUNTY IN SOUTHERN NEW JERSEY...
  EAST CENTRAL SALEM COUNTY IN SOUTHERN NEW JERSEY...

* UNTIL 845 PM EDT

* AT 737 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  SEVERE THUNDERSTORM CAPABLE OF PRODUCING PENNY SIZE HAIL...AND
  DAMAGING WINDS IN EXCESS OF 60 MPH.  THIS STORM WAS LOCATED NEAR
  GREEN LANE...OR 19 MILES SOUTH OF ALLENTOWN...AND MOVING EAST AT 30
  MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
  SOUDERTON...HATFIELD...PERKASIE AND 6 MILES NORTH OF LANSDALE
  AROUND 755 PM EDT...
  FRICKS AROUND 800 PM EDT...
  CHALFONT AND DUBLIN AROUND 805 PM EDT...
  ROBESONIA AROUND 810 PM EDT...
  DOYLESTOWN AND GARDENVILLE AROUND 815 PM EDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO LARGE HAIL AND 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.

&&

LAT...LON 4027 7487 4006 7461 3995 7473 3975 7488
      3956 7510 3998 7541 4019 7562 4023 7571
      4043 7553 4042 7549 4056 7528
TIME...MOT...LOC 2337Z 267DEG 28KT 4032 7549

$$

NIERENBERG

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 18, 7:22 PM EDT	Severe Thunderstorm Warning	PHI	Gloucester, Salem	53 min
Aug 18, 5:45 PM EDT	Severe Thunderstorm Warning	PHI	Berks	60 min
Aug 18, 6:48 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester	72 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2009 Severe Thunderstorm Warnings in New Jersey, 2009 Every severe thunderstorm 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.