Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2019

Severe Thunderstorm Warning 376, NWS Philadelphia/Mount Holly

August 21, 2019Chester County, Montgomery County, Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 21, 2019, 4:07 PM EDT for Chester County, Montgomery County, Pennsylvania. It was in force for 38 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: Aug 21, 2019, 4:07 PM EDT (20:07 UTC)
Expired: Aug 21, 2019, 4:45 PM EDT
In force: 38 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

Counties Chester County, PA, Montgomery County, PA

The radar

The Philadelphia radar (KDIX), 85 km from the middle of the area, began a volume at 20:09 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 21, 4:15 PM EDT	HAIL 0.25	Phoenixville, PA
Aug 21, 4:17 PM EDT	TSTM WND DMG	Phoenixville, PA	SEVERAL LARGE TREE LIMBS SNAPPED. TIME ESTIMATED FROM RADAR.
Aug 21, 4:22 PM EDT	HAIL 0.7	Collegeville, PA	TIME ESTIMATED FROM RADAR.
Aug 21, 4:31 PM EDT	TSTM WND DMG	Plymouth Twp, PA	DOWNED TREE BLOCKING CHELSEA ROAD NEAR CHERRY LANE. TIME ESTIMATED FROM RADAR.

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

The watch it was issued in

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

Issued	Product	Office	Lasted
Aug 21, 3:27 PM EDT	Severe Thunderstorm Watch	SPC	4 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 8.1 hours before the alert went out and 217 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: 190 J/kg
Mixed-layer CIN: -216 J/kg
Mixed-layer LCL: 1166 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 27 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

919 
WUUS51 KPHI 212007
SVRPHI
PAC029-091-212045-
/O.NEW.KPHI.SV.W.0376.190821T2007Z-190821T2045Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
407 PM EDT Wed Aug 21 2019

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Central Montgomery County in southeastern Pennsylvania...
  Northeastern Chester County in southeastern Pennsylvania...

* Until 445 PM EDT.

* At 406 PM EDT, a severe thunderstorm was located over Phoenixville,
  or 14 miles north of West Chester, moving east at 20 mph.

  HAZARD...60 mph wind gusts and quarter size hail.

  SOURCE...Radar indicated.

  IMPACT...Minor damage to vehicles is possible. Wind damage to 
           roofs, siding, trees, and power lines is possible.

* Locations impacted include...
  Norristown, Phoenixville, West Norriton, East Norriton,
  Conshohocken, Ambler, Collegeville, Royersford, Trappe,
  Schwenksville, Bryn Mawr, Valley Forge, Plymouth Meeting, King Of
  Prussia, Radnor Township, Horsham, Skippack, Bridgeport, Spring
  City and North Wales.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

In addition to large hail and damaging winds, frequent cloud to
ground lightning is occurring with this storm. Move indoors
immediately. Remember, if you can hear thunder, you are close enough
to be struck by lightning.

&&

LAT...LON 4027 7558 4020 7512 4019 7512 4002 7530
      4002 7533 4006 7536 4005 7541 4013 7564
TIME...MOT...LOC 2006Z 291DEG 18KT 4016 7551 

HAIL...1.00IN
WIND...60MPH
 
$$

Gorse

2 follow-up statements

447 
WWUS51 KPHI 212017
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
417 PM EDT Wed Aug 21 2019

PAC029-091-212045-
/O.CON.KPHI.SV.W.0376.000000T0000Z-190821T2045Z/
Montgomery PA-Chester PA-
417 PM EDT Wed Aug 21 2019

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 445 PM EDT
FOR SOUTHERN MONTGOMERY AND NORTHEASTERN CHESTER COUNTIES...

At 417 PM EDT, a severe thunderstorm was located over West Norriton,
or 15 miles northeast of West Chester, moving east at 20 mph.

HAZARD...60 mph wind gusts and quarter size hail.

SOURCE...Radar indicated.

IMPACT...Minor damage to vehicles is possible. Wind damage to roofs, 
         siding, trees, and power lines is possible.

Locations impacted include...
Norristown, Phoenixville, West Norriton, East Norriton, Conshohocken,
Ambler, Collegeville, Royersford, Trappe, Schwenksville, Bryn Mawr,
Valley Forge, Plymouth Meeting, King Of Prussia, Radnor Township,
Horsham, Skippack, Bridgeport, Spring City and North Wales.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

Frequent cloud to ground lightning is occurring with this storm. Move
indoors immediately. Lightning is one of nature's leading killers.
Remember, if you can hear thunder, you are close enough to be struck
by lightning.

&&

LAT...LON 4020 7512 4019 7512 4002 7530 4002 7533
      4006 7536 4005 7541 4012 7560 4026 7551
TIME...MOT...LOC 2017Z 291DEG 18KT 4014 7544 

HAIL...1.00IN
WIND...60MPH
 
$$

Gorse

237 
WWUS51 KPHI 212038
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
438 PM EDT Wed Aug 21 2019

PAC029-091-212048-
/O.EXP.KPHI.SV.W.0376.000000T0000Z-190821T2045Z/
Montgomery PA-Chester PA-
438 PM EDT Wed Aug 21 2019

...THE SEVERE THUNDERSTORM WARNING FOR CENTRAL MONTGOMERY AND
NORTHEASTERN CHESTER COUNTIES WILL EXPIRE AT 445 PM EDT...
                
The storm which prompted the warning has weakened below severe
limits, and no longer poses an immediate threat to life or property.
Therefore, the warning will be allowed to expire. However gusty 
winds are still possible with this thunderstorm.

A severe thunderstorm watch remains in effect until 1000 PM EDT for
southeastern Pennsylvania.

LAT...LON 4020 7512 4019 7512 4002 7530 4002 7533
      4006 7536 4005 7541 4012 7560 4026 7551
TIME...MOT...LOC 2038Z 291DEG 18KT 4011 7533 

$$

Gorse

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 21, 3:01 PM EDT	Special Weather Statement	PHI	Berks	29 min
Aug 21, 3:08 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester, Montgomery	34 min
Aug 21, 7:58 PM EDT	Special Weather Statement	PHI	Chester	47 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2019 Every severe thunderstorm warning in 2019

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.