Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 209, NWS Philadelphia/Mount Holly

July 21, 20215 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Jul 21, 2021, 2:14 PM EDT for 5 counties in Pennsylvania. It was in force for 19 min. 2 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: Jul 21, 2021, 2:14 PM EDT (18:14 UTC)
Expired: Jul 21, 2021, 2:33 PM EDT
In force: 19 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

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

The radar

The Philadelphia radar (KDIX), 108 km from the middle of the area, began a volume at 18:18 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
Jul 21, 2:20 PM EDT	TSTM WND DMG	1 Nw West Lawn, PA	PHOTO OF LARGE TREE BRANCHES DOWN ON WIRES IN WEST LAWN PA. TIME ESTIMATED BY SPOTTER.
Jul 21, 2:24 PM EDT	TSTM WND DMG	Spring Twp, PA	LARGE BRANCH DOWN IN SPRING TOWNSHIP, 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
Jul 21, 11:56 AM EDT	Severe Thunderstorm Watch	SPC	7 hr

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 6.2 hours before the alert went out and 212 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: 638 J/kg
Mixed-layer CIN: -61 J/kg
Mixed-layer LCL: 1275 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: -12 m²/s²
0-3 km storm-relative helicity: 95 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

The text

As transmitted.

160 
WUUS51 KPHI 211814
SVRPHI
PAC011-017-029-045-091-211900-
/O.NEW.KPHI.SV.W.0209.210721T1814Z-210721T1900Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
214 PM EDT Wed Jul 21 2021

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Southeastern Berks County in eastern Pennsylvania...
  Montgomery County in southeastern Pennsylvania...
  Central Bucks County in southeastern Pennsylvania...
  Northeastern Chester County in southeastern Pennsylvania...
  Northern Delaware County in southeastern Pennsylvania...

* Until 300 PM EDT.

* At 214 PM EDT, a group of severe thunderstorms were located over 
  Gilbertsville, or 16 miles east of Reading, moving east at 40 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...
  Reading, Norristown, Pottstown, Phoenixville, Lansdale, West
  Norriton, East Norriton, Wyomissing, Doylestown, Conshohocken,
  Hatboro, Souderton, Ambler, Birdsboro, Collegeville, Royersford,
  Chalfont, Sinking Spring, Laureldale and Trappe.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 323 and 337.
 Northeast Extension between mile markers 21 and 38.
 Interstate 76 in Pennsylvania between mile markers 327 and 331.
 Interstate 476 in Pennsylvania between mile markers 17 and 19.
 Interstate 176 in Pennsylvania between mile markers 7 and 11.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4031 7610 4047 7602 4029 7494 4019 7510
      4004 7537
TIME...MOT...LOC 1814Z 277DEG 46KT 4032 7561 

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

NC

1 follow-up statement

687 
WWUS51 KPHI 211833
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
233 PM EDT Wed Jul 21 2021

PAC011-017-029-045-091-211841-
/O.CAN.KPHI.SV.W.0209.000000T0000Z-210721T1900Z/
Berks PA-Montgomery PA-Bucks PA-Chester PA-Delaware PA-
233 PM EDT Wed Jul 21 2021

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN BERKS...
MONTGOMERY...CENTRAL BUCKS...NORTHEASTERN CHESTER AND NORTHERN
DELAWARE COUNTIES 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.  However small hail and
gusty winds are still possible with this thunderstorm.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
eastern and southeastern Pennsylvania.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
Mount Holly NJ.

LAT...LON 4031 7610 4047 7602 4029 7494 4019 7510
      4004 7537
TIME...MOT...LOC 1830Z 277DEG 46KT 4029 7532 

$$

NC

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 21, 1:08 PM EDT	Special Weather Statement	PHI	Lehigh	37 min
Jul 21, 1:11 PM EDT	Special Weather Statement	PHI	Northampton	34 min
Jul 21, 1:27 PM EDT	Severe Thunderstorm Warning	PHI	Berks	48 min
Jul 21, 2:03 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Lehigh, Northampton	42 min
Jul 21, 2:41 PM EDT	Special Weather Statement	PHI	Montgomery	49 min
Jul 21, 2:48 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	42 min
Jul 21, 2:52 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware	38 min
Jul 21, 3:16 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	44 min
Jul 21, 3:27 PM EDT	Severe Thunderstorm Warning	PHI	Chester, Delaware, Philadelphia	33 min
Jul 21, 3:48 PM EDT	Severe Thunderstorm Warning	PHI	Bucks	42 min
Jul 21, 5:59 PM EDT	Special Weather Statement	PHI	Berks	31 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.