Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 309, NWS Philadelphia/Mount Holly

September 23, 20214 counties in Pennsylvania; Gloucester County, Salem County, New Jersey; New Castle County, Delaware

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Sep 23, 2021, 12:12 PM EDT for 4 counties in Pennsylvania; Gloucester County, Salem County, New Jersey; New Castle County, Delaware. It was in force for 48 min. 12 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: Sep 23, 2021, 12:12 PM EDT (16:12 UTC)
Expired: Sep 23, 2021, 1:00 PM EDT
In force: 48 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Tornado: Possible
Hail: 0.75 in
Wind: 60.0 mph

Counties New Castle County, DE, Gloucester County, NJ, Salem County, NJ, Chester County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 100 km from the middle of the area, began a volume at 16:12 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
Sep 23, 12:14 PM EDT	TSTM WND DMG	1 Nnw East Bradford Twp, PA	DOWNED TREE AND WIRES ON CONNER ROAD. TIME ESTIMATED FROM RADAR.
Sep 23, 12:25 PM EDT	TSTM WND DMG	1 Se Paoli, PA	DOWNED TREE ON DARBY PAOLI ROAD. TIME ESTIMATED FROM RADAR.
Sep 23, 12:28 PM EDT	TSTM WND DMG	Berwyn, PA	DOWNED WIRES ON MARGO LANE. TIME ESTIMATED FROM RADAR.
Sep 23, 12:31 PM EDT	TSTM WND DMG	1 Ene Berwyn, PA	DOWNED TREE BLOCKING CONESTOGA ROAD. TIME ESTIMATED FROM RADAR.
Sep 23, 12:31 PM EDT	TSTM WND DMG	2 Sse East Vincent Twp, PA	DOWNED TREE BLOCKING HARES HILL ROAD. TIME BASED ON RADAR.
Sep 23, 12:37 PM EDT	TSTM WND DMG	1 S Villanova, PA	DOWNED TREE LIMBS AND WIRES NEAR WYLDHAVEN ROAD. TIME BASED ON RADAR.
Sep 23, 12:38 PM EDT	TSTM WND DMG	1 Nnw Plymouth Meeting, PA	MPING REPORT OF TREE DAMAGE AT THIS LOCATION. TIME CONFIRMED BY RADAR.
Sep 23, 12:40 PM EDT	TSTM WND DMG	2 Nnw Eagleville, PA	CORRECTS PREVIOUS TSTM WND DMG REPORT FROM 2 NNW EAGLEVILLE. DOWNED TREE LIMBS NEAR RIVER ROAD AND GERMANTOWN PIKE IN LOWER PROVIDENCE TWP. TIME BASED ON RADAR.
Sep 23, 12:40 PM EDT	TSTM WND DMG	2 Nnw Eagleville, PA	DOWNED TREE LIMBS NEAR RIVER ROAD AND GERMANTOWN PIKE IN UPPER PROVIDENCE TWP. TIME BASED ON RADAR.
Sep 23, 12:46 PM EDT	TSTM WND DMG	Plymouth Meeting, PA	SEVERAL REPORTS OF POWER LINES DOWN IN THE CONSHOHOCKEN AND PLYMOUTH MEETING AREAS. TIME ESTIMATED FROM RADAR.
Sep 23, 12:49 PM EDT	TSTM WND DMG	1 Ne East Norriton, PA	DOWNED TREE LIMBS AND WIRES NEAR MAUCK ROAD. TIME ESTIMATED FROM RADAR.
Sep 23, 12:49 PM EDT	TSTM WND DMG	1 Nw Blue Bell, PA	DOWNED TREE NEAR THE INTERSECTION OF BOXWOOD LANE AND HEMLOCK DRIVE. TIME BASED ON RADAR.

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

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 4.2 hours before the alert went out and 202 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 517 m above ground
0-6 km bulk shear: 58 kt
0-1 km storm-relative helicity: -71 m²/s²
0-3 km storm-relative helicity: 88 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 2.0

Open this sounding in Storm Lab

The text

As transmitted.

175 
WUUS51 KPHI 231612
SVRPHI
DEC003-NJC015-033-PAC029-045-091-101-231700-
/O.NEW.KPHI.SV.W.0309.210923T1612Z-210923T1700Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
1212 PM EDT Thu Sep 23 2021

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Northeastern New Castle County in northern Delaware...
  Northwestern Salem County in southern New Jersey...
  Northwestern Gloucester County in southern New Jersey...
  Montgomery County in southeastern Pennsylvania...
  Eastern Chester County in southeastern Pennsylvania...
  Northwestern Philadelphia County in southeastern Pennsylvania...
  Delaware County in southeastern Pennsylvania...

* Until 100 PM EDT.

* At 1212 PM EDT, severe thunderstorms were located along a line
  extending from near Marshallton to Westtown to Penns Grove, moving
  north at 45 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

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

* Locations impacted include...
  Philadelphia, Wilmington, West Chester, Norristown, Chester,
  Pottstown, Phoenixville, Lansdale, West Norriton, East Norriton,
  Pennsville, Yeadon, Westtown, Carneys Point, Downingtown,
  Conshohocken, Folcroft, Swarthmore, Kennett Square and New Castle.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 309 and 337.
 Northeast Extension between mile markers 21 and 38.
 Interstate 95 in Pennsylvania between mile markers 0 and 9.
 Interstate 95 in Delaware between mile markers 13 and 23.
 Interstate 76 in Pennsylvania between mile markers 327 and 340.
 Interstate 295 in New Jersey between mile markers 0 and 9.
 Interstate 476 in Pennsylvania between mile markers 0 and 19.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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

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

&&

LAT...LON 4026 7569 4029 7566 4033 7563 4036 7538
      4006 7516 3959 7548 3983 7564 3984 7579
TIME...MOT...LOC 1612Z 199DEG 38KT 3991 7571 3992 7557 3974 7547 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Staarmann

3 follow-up statements

054 
WWUS51 KPHI 231622
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
1222 PM EDT Thu Sep 23 2021

DEC003-NJC015-033-PAC029-045-091-101-231700-
/O.CON.KPHI.SV.W.0309.000000T0000Z-210923T1700Z/
New Castle DE-Salem NJ-Gloucester NJ-Montgomery PA-Chester PA-
Philadelphia PA-Delaware PA-
1222 PM EDT Thu Sep 23 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 100 PM EDT
FOR NORTHEASTERN NEW CASTLE...NORTHWESTERN SALEM...NORTHWESTERN
GLOUCESTER...MONTGOMERY...NORTHEASTERN CHESTER...NORTHWESTERN
PHILADELPHIA AND DELAWARE COUNTIES...

At 1221 PM EDT, severe thunderstorms were located along a line
extending from Downingtown to near Paoli to near Chester Township,
moving northeast at 45 mph.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

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

Locations impacted include...
Philadelphia, Wilmington, West Chester, Norristown, Chester,
Pottstown, Phoenixville, Lansdale, West Norriton, East Norriton,
Pennsville, Yeadon, Westtown, Carneys Point, Downingtown,
Conshohocken, Folcroft, Swarthmore, Penns Grove and Collegeville.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 309 and 337.
 Northeast Extension between mile markers 21 and 38.
 Interstate 95 in Pennsylvania between mile markers 0 and 9.
 Interstate 95 in Delaware between mile markers 17 and 23.
 Interstate 76 in Pennsylvania between mile markers 327 and 340.
 Interstate 295 in New Jersey between mile markers 2 and 10.
 Interstate 476 in Pennsylvania between mile markers 0 and 19.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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

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

&&

LAT...LON 4025 7569 4033 7562 4036 7538 4006 7516
      3967 7542 3969 7551 3992 7558 3995 7576
TIME...MOT...LOC 1621Z 203DEG 41KT 4000 7567 4001 7553 3981 7540 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Staarmann

541 
WWUS51 KPHI 231634
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
1234 PM EDT Thu Sep 23 2021

DEC003-231644-
/O.CAN.KPHI.SV.W.0309.000000T0000Z-210923T1700Z/
New Castle DE-
1234 PM EDT Thu Sep 23 2021

...THE SEVERE THUNDERSTORM WARNING FOR NORTHEASTERN NEW CASTLE COUNTY
IS CANCELLED...

The storms which prompted the warning have moved out of the warned 
area. Therefore, the warning has been cancelled.

LAT...LON 4025 7569 4033 7562 4036 7539 4006 7516
      3967 7542 3968 7547 3978 7545 3980 7541
      3982 7544 3986 7543 4003 7549 4010 7572
TIME...MOT...LOC 1634Z 200DEG 40KT 4019 7561 4016 7544 3991 7531 

$$

NJC015-033-PAC029-045-091-101-231700-
/O.CON.KPHI.SV.W.0309.000000T0000Z-210923T1700Z/
Salem NJ-Gloucester NJ-Montgomery PA-Chester PA-Philadelphia PA-
Delaware PA-
1234 PM EDT Thu Sep 23 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 100 PM EDT
FOR NORTHWESTERN SALEM...NORTHWESTERN GLOUCESTER...MONTGOMERY...
NORTHEASTERN CHESTER...NORTHWESTERN PHILADELPHIA AND DELAWARE
COUNTIES...

At 1234 PM EDT, severe thunderstorms were located along a line
extending from near Pughtown to Collegeville to Darby Township,
moving north at 45 mph.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

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

Locations impacted include...
Philadelphia, Norristown, Chester, Pottstown, Phoenixville, West
Norriton, East Norriton, Yeadon, Carneys Point, Conshohocken,
Folcroft, Swarthmore, Collegeville, Royersford, Narberth, Trappe,
East Lansdowne, Schwenksville, Green Lane and Pughtown.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 316 and 337.
 Northeast Extension between mile markers 21 and 38.
 Interstate 95 in Pennsylvania between mile markers 1 and 9.
 Interstate 76 in Pennsylvania between mile markers 327 and 340.
 Interstate 295 in New Jersey between mile markers 4 and 10.
 Interstate 476 in Pennsylvania between mile markers 0 and 19.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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

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

&&

LAT...LON 4025 7569 4033 7562 4036 7539 4006 7516
      3967 7542 3968 7547 3978 7545 3980 7541
      3982 7544 3986 7543 4003 7549 4010 7572
TIME...MOT...LOC 1634Z 200DEG 40KT 4019 7561 4016 7544 3991 7531 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Staarmann

645 
WWUS51 KPHI 231645
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
1245 PM EDT Thu Sep 23 2021

NJC033-PAC029-231655-
/O.CAN.KPHI.SV.W.0309.000000T0000Z-210923T1700Z/
Salem NJ-Chester PA-
1245 PM EDT Thu Sep 23 2021

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN SALEM AND
NORTHEASTERN CHESTER COUNTIES IS CANCELLED...

The storms which prompted the warning have moved out of the warned 
area. Therefore, the warning has been cancelled.

LAT...LON 4033 7562 4036 7539 4006 7516 3974 7537
      3982 7544 4000 7536 4007 7536 4010 7545
      4013 7546 4014 7551 4016 7550 4015 7552
      4024 7560 4022 7561 4024 7565 4024 7569
TIME...MOT...LOC 1645Z 199DEG 38KT 4029 7556 4026 7539 4001 7526 

$$

NJC015-PAC045-091-101-231700-
/O.CON.KPHI.SV.W.0309.000000T0000Z-210923T1700Z/
Gloucester NJ-Montgomery PA-Philadelphia PA-Delaware PA-
1245 PM EDT Thu Sep 23 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 100 PM EDT
FOR NORTHWESTERN GLOUCESTER...MONTGOMERY...NORTHWESTERN PHILADELPHIA
AND EASTERN DELAWARE COUNTIES...

At 1245 PM EDT, severe thunderstorms were located along a line
extending from near Gilbertsville to near Spring Mount to Narberth,
moving north at 45 mph.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

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

Locations impacted include...
Philadelphia, Norristown, Chester, Pottstown, Phoenixville, West
Norriton, East Norriton, Yeadon, Conshohocken, Folcroft, Swarthmore,
Collegeville, Royersford, Narberth, Trappe, East Lansdowne,
Schwenksville, Green Lane, Darby Township and Morris Park.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 326 and 337.
 Northeast Extension between mile markers 21 and 38.
 Interstate 95 in Pennsylvania between mile markers 1 and 9.
 Interstate 76 in Pennsylvania between mile markers 327 and 340.
 Interstate 295 in New Jersey between mile markers 10 and 11.
 Interstate 476 in Pennsylvania between mile markers 0 and 11, and
between mile markers 13 and 19.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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

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

&&

LAT...LON 4033 7562 4036 7539 4006 7516 3974 7537
      3982 7544 4000 7536 4007 7536 4010 7545
      4013 7546 4014 7551 4016 7550 4015 7552
      4024 7560 4022 7561 4024 7565 4024 7569
TIME...MOT...LOC 1645Z 199DEG 38KT 4029 7556 4026 7539 4001 7526 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Staarmann

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 23, 9:12 AM EDT	Coastal Flood Advisory	PHI	Bucks, Delaware, Philadelphia	10 hr
Sep 23, 10:52 AM EDT	Areal Flood Advisory	PHI	Chester	3 hr
Sep 23, 11:33 AM EDT	Areal Flood Advisory	PHI	Berks, Chester, Delaware, Montgomery, Philadelphia	3 hr
Sep 23, 11:40 AM EDT	Areal Flood Advisory	PHI	Berks, Bucks, Carbon, Lehigh, Montgomery, Northampton	3 hr
Sep 23, 11:57 AM EDT	Flash Flood Warning	PHI	Chester, Delaware	3 hr
Sep 23, 12:28 PM EDT	Flash Flood Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	4 hr
Sep 23, 12:54 PM EDT	Special Weather Statement	PHI	Philadelphia	51 min
Sep 23, 12:56 PM EDT	Areal Flood Advisory	PHI	Bucks, Carbon, Lehigh, Monroe, Montgomery, Northampton and 1 more	3 hr
Sep 23, 12:57 PM EDT	Special Weather Statement	PHI	Bucks	33 min
Sep 23, 1:13 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Delaware, Montgomery, Philadelphia	47 min
Sep 23, 1:42 PM EDT	Flash Flood Warning	PHI	Bucks, Delaware, Montgomery, Philadelphia	4 hr
Sep 23, 1:48 PM EDT	River Flood Warning	PHI	Chester	5 hr
Sep 23, 1:58 PM EDT	Special Weather Statement	PHI	Bucks	32 min
Sep 23, 2:37 PM EDT	Areal Flood Advisory	PHI	Bucks, Northampton	3 hr
Sep 23, 3:26 PM EDT	Flash Flood Warning	PHI	Bucks	2 hr
Sep 23, 4:26 PM EDT	Areal Flood Warning	PHI	Chester, Delaware, Montgomery, Philadelphia	80 min
Sep 23, 7:18 PM EDT	Areal Flood Warning	PHI	Berks, Montgomery	36 min
Sep 22, 8:43 PM EDT	Gale Warning	PHI		18 hr
Sep 23, 2:47 PM EDT	Special Weather Statement	PHI	Hunterdon, Mercer	28 min
Sep 23, 2:52 PM EDT	Special Weather Statement	PHI	Camden	23 min
Sep 23, 3:13 PM EDT	Special Weather Statement	PHI	Mercer, Somerset	32 min
Sep 23, 3:16 PM EDT	Special Weather Statement	PHI	Burlington	29 min
Sep 23, 3:23 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Mercer, Middlesex, Morris, Somerset	52 min
Sep 23, 3:50 PM EDT	Special Weather Statement	PHI	Burlington	25 min
Sep 23, 4:21 PM EDT	Areal Flood Advisory	PHI	Middlesex, Monmouth, Morris, Ocean, Somerset, Sussex	15 min
Sep 23, 4:36 PM EDT	Flash Flood Warning	PHI	Middlesex, Monmouth, Morris, Somerset, Sussex	3 hr
Sep 23, 5:00 PM EDT	Special Weather Statement	PHI	Monmouth	30 min
Sep 23, 11:11 AM EDT	Special Weather Statement	PHI	New Castle	64 min
Sep 23, 11:42 AM EDT	Severe Thunderstorm Warning	PHI	New Castle	33 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2021 Severe Thunderstorm Warnings in New Jersey, 2021 Severe Thunderstorm Warnings in Delaware, 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.