Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 170, NWS Philadelphia/Mount Holly

July 12, 2021Chester County, Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Jul 12, 2021, 5:41 PM EDT for Chester County, Pennsylvania. It was in force for 34 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: Jul 12, 2021, 5:41 PM EDT (21:41 UTC)
Expired: Jul 12, 2021, 6:15 PM EDT
In force: 34 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

County Chester County, PA

The radar

The Philadelphia radar (KDIX), 126 km from the middle of the area, began a volume at 21:43 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
Jul 12, 3:34 PM EDT	Severe Thunderstorm Watch	SPC	5 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 9.7 hours before the alert went out and 171 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: 974 J/kg
Mixed-layer CIN: -83 J/kg
Mixed-layer LCL: 724 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: 10 m²/s²
0-3 km storm-relative helicity: 53 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.8

Open this sounding in Storm Lab

The text

As transmitted.

147 
WUUS51 KPHI 122141
SVRPHI
PAC029-122300-
/O.NEW.KPHI.SV.W.0170.210712T2141Z-210712T2300Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
541 PM EDT Mon Jul 12 2021

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Chester County in southeastern Pennsylvania...

* Until 700 PM EDT.

* At 540 PM EDT, a severe thunderstorm was located over Gap, or 7
  miles southeast of New Holland, moving east at 20 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Damage to roofs, siding, trees, and power lines is 
           possible.

* Locations impacted include...
  West Chester, Coatesville, Downingtown, Kennett Square, Parkesburg,
  West Grove, Honey Brook, Elverson, Homeville, Cochranville,
  Marshallton, Lionville-Marchwood, Glenmoore, Chester Springs,
  Lionville, Hockessin, West Goshen, Malvern, Atglen and South
  Coatesville.

This includes Pennsylvania Turnpike between mile markers 300 and 321.
 
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.

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 3987 7599 3992 7600 3994 7598 3995 7600
      4004 7593 4011 7594 4016 7584 4010 7548
      3982 7565 3980 7569 3985 7601 3987 7601
TIME...MOT...LOC 2140Z 281DEG 19KT 4001 7600 

HAIL...<.75IN
WIND...60MPH
 
$$

CMS

2 follow-up statements

925 
WWUS51 KPHI 122207
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
607 PM EDT Mon Jul 12 2021

PAC029-122300-
/O.CON.KPHI.SV.W.0170.000000T0000Z-210712T2300Z/
Chester PA-
607 PM EDT Mon Jul 12 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 700 PM EDT
FOR CHESTER COUNTY...

At 605 PM EDT, a severe thunderstorm was located over Quarryville, 
or near Willow Street, moving east at 20 mph. The storms near 
Coatesville have weakened, but storms farther west in Lancaster 
County may yet produce damaging winds as they enter Chester County 
in the next hour.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

IMPACT...Damage to roofs, siding, trees, and power lines is 
         possible.

Locations impacted include...
West Chester, Coatesville, Downingtown, Kennett Square, Parkesburg,
West Grove, Honey Brook, Elverson, Homeville, Cochranville,
Marshallton, Lionville-Marchwood, Glenmoore, Chester Springs,
Lionville, Hockessin, West Goshen, Malvern, Atglen and South
Coatesville.

This includes Pennsylvania Turnpike between mile markers 300 and 321.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3987 7599 3992 7600 3994 7598 3995 7600
      4004 7593 4011 7594 4016 7584 4010 7548
      3982 7565 3980 7569 3985 7601 3987 7601
TIME...MOT...LOC 2205Z 279DEG 18KT 3992 7619 

HAIL...<.75IN
WIND...60MPH
 
$$

CMS

798 
WWUS51 KPHI 122215
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
615 PM EDT Mon Jul 12 2021

PAC029-122225-
/O.CAN.KPHI.SV.W.0170.000000T0000Z-210712T2300Z/
Chester PA-
615 PM EDT Mon Jul 12 2021

...THE SEVERE THUNDERSTORM WARNING FOR CHESTER COUNTY IS CANCELLED...
                
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 has been cancelled.

A Severe Thunderstorm Watch remains in effect until 1100 PM EDT for
northern Delaware...and eastern and southeastern Pennsylvania.

LAT...LON 3987 7599 3992 7600 3994 7598 3995 7600
      4004 7593 4011 7594 4016 7584 4010 7548
      3982 7565 3980 7569 3985 7601 3987 7601
TIME...MOT...LOC 2212Z 281DEG 19KT 3991 7612 

$$

CMS

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 11, 10:21 PM EDT	Severe Thunderstorm Warning	PHI	Berks	24 min
Jul 11, 10:22 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Carbon, Lehigh, Monroe, Northampton	38 min
Jul 12, 1:59 PM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery, Philadelphia	3 hr
Jul 12, 2:12 PM EDT	Flash Flood Warning Emergency	PHI	Bucks, Philadelphia	7 hr
Jul 12, 2:28 PM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Jul 12, 3:08 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Philadelphia	67 min
Jul 12, 4:16 PM EDT	Areal Flood Advisory	PHI	Bucks, Montgomery, Philadelphia	114 min
Jul 12, 5:08 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Delaware, Montgomery, Philadelphia	67 min
Jul 12, 5:26 PM EDT	Areal Flood Advisory	PHI	Delaware, Montgomery, Philadelphia	2 hr
Jul 12, 6:01 PM EDT	Flash Flood Warning	PHI	Philadelphia	102 min
Jul 12, 6:18 PM EDT	Flash Flood Warning	PHI	Delaware	84 min
Jul 12, 7:06 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	69 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2021 Every severe thunderstorm warning in 2021

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.