Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021
Severe Thunderstorm Warning 251, NWS Philadelphia/Mount Holly
NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 11, 2021, 6:26 PM EDT for 4 counties in Pennsylvania; New Castle County, Delaware. It was in force for 49 min. 5 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 11, 2021, 6:26 PM EDT (22:26 UTC)
- Expired
- Aug 11, 2021, 7:15 PM EDT
- In force
- 49 min
- Issued by
- NWS Philadelphia/Mount Holly
- Area
- Storm-based polygon
- Hail
- 0.75 in
- Wind
- 60.0 mph
Counties New Castle County, DE, Berks County, PA, Chester County, PA, Delaware County, PA, Montgomery County, PA
The radar
The Philadelphia radar (KDIX), 121 km from the middle of the area, began a volume at 22:27 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 11, 6:48 PM EDT | TSTM WND DMG | Cedarville, PA | TREE DOWN AND BLOCKING SHEEPHILL ROAD. TIME ESTIMATED FROM RADAR. |
| Aug 11, 6:48 PM EDT | TSTM WND DMG | South Pottstown, PA | TREES AND WIRES BLOCKING RIVER ROAD, THE TREE FELL ON AN UNOCCUPIED PARKED VEHICLE. TIME ESTIMATED FROM RADAR. |
| Aug 11, 7:06 PM EDT | TSTM WND DMG | West Chester, PA | TREE BLOCKING ROUTE 3, ALONG THE WEST CHESTER PIKE NEAR WESTTOWN ROAD. TIME ESTIMATED FROM RADAR. |
| Aug 11, 7:14 PM EDT | TSTM WND DMG | 1 Nnw West Norriton, PA | TREE DOWN ON TOP OF WIRES AND BLOCKING THE STREET AT GALBRAITH AVE AND WEST MAIN STREET. |
| Aug 11, 7:15 PM EDT | TSTM WND DMG | 1 N Willistown Twp, PA | TREE DOWN IN ROADWAY ON GOSHEN ROAD. 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 11, 3:02 PM EDT | Severe Thunderstorm Watch | SPC | 6 hr |
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 10.4 hours before the alert went out and 177 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.
- Mixed-layer CAPE
- 553 J/kg
- Mixed-layer CIN
- -190 J/kg
- Mixed-layer LCL
- 1301 m above ground
- 0-6 km bulk shear
- 13 kt
- 0-1 km storm-relative helicity
- 20 m²/s²
- 0-3 km storm-relative helicity
- 77 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
811
WUUS51 KPHI 112226
SVRPHI
DEC003-PAC011-029-045-091-112315-
/O.NEW.KPHI.SV.W.0251.210811T2226Z-210811T2315Z/
BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
626 PM EDT Wed Aug 11 2021
The National Weather Service in Mount Holly NJ has issued a
* Severe Thunderstorm Warning for...
Northern New Castle County in northern Delaware...
Southeastern Berks County in eastern Pennsylvania...
Southwestern Montgomery County in southeastern Pennsylvania...
Chester County in southeastern Pennsylvania...
Western Delaware County in southeastern Pennsylvania...
* Until 715 PM EDT.
* At 626 PM EDT, severe thunderstorms were located along a line
extending from near Elverson to near Rising Sun, moving east at 40
mph.
HAZARD...60 mph wind gusts and penny size hail.
SOURCE...Radar indicated.
IMPACT...Damage to roofs, siding, trees, and power lines is
possible.
* Locations impacted include...
Wilmington, Newark, West Chester, Norristown, Pottstown,
Phoenixville, West Norriton, East Norriton, Pennsville,
Coatesville, Westtown, Downingtown, Elsmere, Kennett Square, New
Castle, Birdsboro, Collegeville, Oxford, Royersford and Parkesburg.
This includes the following highways...
Pennsylvania Turnpike between mile markers 298 and 331.
Northeast Extension between mile markers 24 and 27.
Interstate 95 in Pennsylvania near mile marker 0.
Interstate 95 in Delaware between mile markers 6 and 23.
Interstate 76 in Pennsylvania between mile markers 327 and 330.
Interstate 295 in New Jersey near mile marker 0.
Interstate 476 in Pennsylvania between mile markers 12 and 14.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
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 3973 7610 3987 7599 3995 7600 4004 7593
4009 7594 4012 7592 4014 7588 4016 7590
4036 7577 4034 7562 4019 7528 3967 7551
3966 7579 3972 7579
TIME...MOT...LOC 2226Z 266DEG 36KT 4019 7576 3972 7609
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...0.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH
$$
JEO2 follow-up statements
181
WWUS51 KPHI 112249
SVSPHI
Severe Weather Statement
National Weather Service Mount Holly NJ
649 PM EDT Wed Aug 11 2021
DEC003-PAC011-029-045-091-112315-
/O.CON.KPHI.SV.W.0251.000000T0000Z-210811T2315Z/
New Castle DE-Berks PA-Montgomery PA-Chester PA-Delaware PA-
649 PM EDT Wed Aug 11 2021
...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 715 PM EDT
FOR NORTHERN NEW CASTLE...SOUTHEASTERN BERKS...SOUTHWESTERN
MONTGOMERY...CHESTER AND WESTERN DELAWARE COUNTIES...
At 649 PM EDT, severe thunderstorms were located along a line
extending from Trappe to Kemblesville, moving east at 40 mph.
HAZARD...60 mph wind gusts and penny size hail.
SOURCE...Radar indicated.
IMPACT...Damage to roofs, siding, trees, and power lines is
possible.
Locations impacted include...
Wilmington, West Chester, Norristown, Pottstown, Phoenixville, West
Norriton, East Norriton, Coatesville, Westtown, Downingtown, Elsmere,
Kennett Square, Birdsboro, Collegeville, Oxford, Royersford,
Parkesburg, Trappe, West Grove and Honey Brook.
This includes the following highways...
Pennsylvania Turnpike between mile markers 298 and 331.
Northeast Extension between mile markers 24 and 27.
Interstate 95 in Pennsylvania near mile marker 0.
Interstate 95 in Delaware between mile markers 13 and 23.
Interstate 76 in Pennsylvania between mile markers 327 and 330.
Interstate 476 in Pennsylvania between mile markers 12 and 14.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
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 3987 7599 3994 7598 3995 7600 4004 7593
4009 7594 4012 7592 4014 7588 4016 7590
4036 7577 4034 7562 4019 7528 3972 7549
3972 7579 3975 7602 3979 7605
TIME...MOT...LOC 2249Z 266DEG 36KT 4020 7548 3973 7581
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...0.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH
$$
JEO308
WWUS51 KPHI 112313
SVSPHI
Severe Weather Statement
National Weather Service Mount Holly NJ
713 PM EDT Wed Aug 11 2021
DEC003-PAC011-029-045-091-112322-
/O.EXP.KPHI.SV.W.0251.000000T0000Z-210811T2315Z/
New Castle DE-Berks PA-Montgomery PA-Chester PA-Delaware PA-
713 PM EDT Wed Aug 11 2021
...THE SEVERE THUNDERSTORM WARNING FOR NORTHERN NEW CASTLE...
SOUTHEASTERN BERKS...SOUTHWESTERN MONTGOMERY...CHESTER AND WESTERN
DELAWARE COUNTIES WILL EXPIRE AT 715 PM EDT...
The storms which prompted the warning have moved out of part of the
warned area. Therefore, the warning will be allowed to expire.
However, a new Severe Thunderstorm Warning has been issued for
portions of this original warning where severe thunderstorms
continue.
A Severe Thunderstorm Watch remains in effect until 900 PM EDT for
northern Delaware...and eastern and southeastern Pennsylvania.
LAT...LON 3987 7599 3994 7598 3995 7600 4004 7593
4009 7594 4012 7592 4014 7588 4016 7590
4036 7577 4034 7562 4019 7528 3972 7549
3972 7579 3975 7602 3979 7605
TIME...MOT...LOC 2312Z 266DEG 36KT 4021 7520 3974 7553
$$
JEOThe office that day
Everything else NWS Philadelphia/Mount Holly issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 10, 8:02 PM EDT | Severe Thunderstorm Warning | PHI | Delaware, Philadelphia | 43 min |
| Aug 10, 8:18 PM EDT | Severe Thunderstorm Warning | PHI | Chester, Delaware, Montgomery | 42 min |
| Aug 10, 8:36 PM EDT | Severe Thunderstorm Warning | PHI | Bucks, Delaware, Montgomery, Philadelphia | 39 min |
| Aug 10, 8:43 PM EDT | Areal Flood Advisory | PHI | Delaware, Montgomery, Philadelphia | 2 hr |
| Aug 11, 2:56 PM EDT | Excessive Heat Watch | PHI | Berks, Bucks, Chester, Lehigh, Montgomery, Northampton | 12 hr |
| Aug 11, 4:46 PM EDT | Special Weather Statement | PHI | Monroe | 44 min |
| Aug 11, 4:58 PM EDT | Special Weather Statement | PHI | Berks | 47 min |
| Aug 11, 5:20 PM EDT | Areal Flood Advisory | PHI | Carbon, Monroe | 57 min |
| Aug 11, 5:48 PM EDT | Severe Thunderstorm Warning | PHI | Berks | 57 min |
| Aug 11, 6:16 PM EDT | Severe Thunderstorm Warning | PHI | Berks, Lehigh, Montgomery | 44 min |
| Aug 11, 6:48 PM EDT | Severe Thunderstorm Warning | PHI | Bucks, Lehigh, Montgomery, Northampton | 42 min |
| Aug 11, 6:50 PM EDT | Areal Flood Advisory | PHI | Monroe, Northampton | 3 hr |
| Aug 11, 7:04 PM EDT | Areal Flood Advisory | PHI | Berks, Bucks, Chester, Delaware, Lehigh, Montgomery and 2 more | 2 hr |
| Aug 11, 7:11 PM EDT | Severe Thunderstorm Warning | PHI | Bucks, Chester, Delaware, Montgomery, Philadelphia | 49 min |
| Aug 10, 8:11 PM EDT | Special Weather Statement | PHI | New Castle | 34 min |
| Aug 10, 9:09 PM EDT | Special Weather Statement | PHI | Sussex | 36 min |
Nearby
Severe Thunderstorm Warnings in Pennsylvania, 2021Severe Thunderstorm Warnings in Delaware, 2021Every 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.