Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 241, NWS Philadelphia/Mount Holly

August 10, 20218 counties in Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 10, 2021, 4:33 PM EDT for 8 counties in Pennsylvania. It was in force for 42 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: Aug 10, 2021, 4:33 PM EDT (20:33 UTC)
Expired: Aug 10, 2021, 5:15 PM EDT
In force: 42 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

Counties Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Lehigh County, PA, Monroe County, PA, Montgomery County, PA, Northampton County, PA

The radar

The Philadelphia radar (KDIX), 109 km from the middle of the area, began a volume at 20:32 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 10, 4:35 PM EDT	TSTM WND DMG	1 Wnw Emmaus, PA	CORRECTS TIME OF PREVIOUS TSTM WND DMG REPORT FROM 1 WNW EMMAUS. COUNTY DISPATCH REPORTS ABOUT 5 INSTANCES OF DOWNED TREES AND LIMBS OVER THE SOUTHERN PORTION OF LEHIGH COUNTY. TIME ESTIMATED FROM RADAR.
Aug 10, 5:00 PM EDT	TSTM WND DMG	Easton, PA	A FEW REPORTS OF DOWNED TREES AND POWER OUTAGES NEAR EASTON. TIME ESTIMATED FROM 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, 8.6 hours before the alert went out and 229 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: 529 J/kg
Mixed-layer CIN: -120 J/kg
Mixed-layer LCL: 1096 m above ground
0-6 km bulk shear: 14 kt
0-1 km storm-relative helicity: 37 m²/s²
0-3 km storm-relative helicity: 65 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

408 
WUUS51 KPHI 102033
SVRPHI
PAC011-017-025-029-077-089-091-095-102115-
/O.NEW.KPHI.SV.W.0241.210810T2033Z-210810T2115Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
433 PM EDT Tue Aug 10 2021

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Southeastern Berks County in eastern Pennsylvania...
  Eastern Lehigh County in eastern Pennsylvania...
  Montgomery County in southeastern Pennsylvania...
  Southeastern Carbon County in northeastern Pennsylvania...
  Northwestern Bucks County in southeastern Pennsylvania...
  Northeastern Chester County in southeastern Pennsylvania...
  South central Monroe County in northeastern Pennsylvania...
  Northampton County in eastern Pennsylvania...

* Until 515 PM EDT.

* At 432 PM EDT, severe thunderstorms were located along a line
  extending from Palmerton to Emmaus to Elverson, moving east at 35
  mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

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

* Locations impacted include...
  Allentown, Easton, Lehighton, Bethlehem, Norristown, Pottstown,
  Phoenixville, Lansdale, West Norriton, Forks, East Norriton,
  Emmaus, Northampton, Quakertown, Perkasie, Wilson, Souderton,
  Bedminster, Hellertown and Nazareth.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 296 and 328.
 Northeast Extension between mile markers 24 and 79.
 Interstate 76 in Pennsylvania between mile markers 327 and 328.
 Interstate 78 in Pennsylvania between mile markers 54 and 76.
 Interstate 176 in Pennsylvania between mile markers 1 and 3.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Wind damage with these storms will occur before any rain or
lightning. Do not wait for the sound of thunder before taking cover.
SEEK SHELTER IMMEDIATELY inside a sturdy structure and stay away from
windows.

&&

LAT...LON 4055 7556 4089 7575 4083 7527 4066 7519
      4057 7519 4058 7515 4042 7507 3998 7546
      4009 7594 4012 7593 4014 7588 4018 7594
TIME...MOT...LOC 2032Z 287DEG 28KT 4081 7563 4053 7547 4015 7586 

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

$$

SFJ

2 follow-up statements

649 
WWUS51 KPHI 102056
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
456 PM EDT Tue Aug 10 2021

PAC011-017-025-029-077-089-091-095-102115-
/O.CON.KPHI.SV.W.0241.000000T0000Z-210810T2115Z/
Berks PA-Lehigh PA-Montgomery PA-Carbon PA-Bucks PA-Chester PA-
Monroe PA-Northampton PA-
456 PM EDT Tue Aug 10 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 515 PM EDT
FOR SOUTHEASTERN BERKS...EASTERN LEHIGH...MONTGOMERY...SOUTHEASTERN
CARBON...NORTHWESTERN BUCKS...NORTHEASTERN CHESTER...SOUTH CENTRAL
MONROE AND NORTHAMPTON COUNTIES...

At 456 PM EDT, severe thunderstorms were located along a line
extending from near Beersville to near Pleasant Valley to near
Chester Springs, moving east at 30 mph.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

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

Locations impacted include...
Allentown, Easton, Bethlehem, Norristown, Pottstown, Phoenixville,
Lansdale, West Norriton, Forks, East Norriton, Emmaus, Northampton,
Quakertown, Perkasie, Wilson, Souderton, Bedminster, Hellertown,
Nazareth and Palmerton.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 296 and 328.
 Northeast Extension between mile markers 24 and 51.
 Interstate 76 in Pennsylvania between mile markers 327 and 328.
 Interstate 78 in Pennsylvania between mile markers 57 and 76.
 Interstate 176 in Pennsylvania between mile markers 1 and 3.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Wind damage with these storms will occur before any rain or
lightning. Do not wait for the sound of thunder before taking cover.
SEEK SHELTER IMMEDIATELY inside a sturdy structure and stay away from
windows.

&&

LAT...LON 4052 7551 4087 7562 4083 7527 4066 7519
      4057 7519 4058 7515 4042 7507 3998 7546
      4009 7594 4012 7593 4014 7588 4018 7594
TIME...MOT...LOC 2056Z 287DEG 28KT 4076 7543 4048 7527 4010 7566 

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

$$

SFJ

116 
WWUS51 KPHI 102107
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
507 PM EDT Tue Aug 10 2021

PAC025-089-095-102116-
/O.CAN.KPHI.SV.W.0241.000000T0000Z-210810T2115Z/
Carbon PA-Monroe PA-Northampton PA-
507 PM EDT Tue Aug 10 2021

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN CARBON...SOUTH
CENTRAL MONROE AND NORTHAMPTON COUNTIES IS CANCELLED...

The storms which prompted the warning have weakened. Therefore, the 
warning has been cancelled.

LAT...LON 4012 7593 4014 7588 4052 7551 4057 7515
      4042 7507 3998 7546 4009 7594
TIME...MOT...LOC 2106Z 287DEG 28KT 4074 7533 4046 7517 4008 7556 

$$

PAC011-017-029-077-091-102115-
/O.CON.KPHI.SV.W.0241.000000T0000Z-210810T2115Z/
Berks PA-Lehigh PA-Montgomery PA-Bucks PA-Chester PA-
507 PM EDT Tue Aug 10 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 515 PM EDT
FOR SOUTHEASTERN BERKS...SOUTHEASTERN LEHIGH...MONTGOMERY...
NORTHWESTERN BUCKS AND NORTHEASTERN CHESTER COUNTIES...

At 506 PM EDT, severe thunderstorms were located along a line
extending from Nazareth to Ottsville to near Chester Springs, moving
east at 30 mph.

HAZARD...60 mph wind gusts.

SOURCE...Radar indicated.

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

Locations impacted include...
Norristown, Pottstown, Phoenixville, Lansdale, West Norriton, East
Norriton, Emmaus, Quakertown, Perkasie, Souderton, Bedminster,
Collegeville, Royersford, Chalfont, Tinicum, Trappe, Hatfield, East
Greenville, Dublin and Honey Brook.

This includes the following highways...
 Pennsylvania Turnpike between mile markers 300 and 328.
 Northeast Extension between mile markers 24 and 51.
 Interstate 76 in Pennsylvania between mile markers 327 and 328.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Wind damage with these storms will occur before any rain or
lightning. Do not wait for the sound of thunder before taking cover.
SEEK SHELTER IMMEDIATELY inside a sturdy structure and stay away from
windows.

&&

LAT...LON 4012 7593 4014 7588 4052 7551 4057 7515
      4042 7507 3998 7546 4009 7594
TIME...MOT...LOC 2106Z 287DEG 28KT 4074 7533 4046 7517 4008 7556 

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

$$

SFJ

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 9, 10:10 PM EDT	Areal Flood Advisory	PHI	Carbon	3 hr
Aug 10, 3:33 AM EDT	Excessive Heat Warning	PHI	Berks, Bucks, Chester, Delaware, Lehigh, Montgomery and 2 more	4 days
Aug 10, 3:33 AM EDT	Heat Advisory	PHI	Berks, Carbon, Lehigh, Monroe, Northampton	4 days
Aug 10, 5:58 AM EDT	Flash Flood Warning	PHI	Bucks	2 hr
Aug 10, 3:06 PM EDT	Special Weather Statement	PHI	Berks	24 min
Aug 10, 3:33 PM EDT	Special Weather Statement	PHI	Berks	27 min
Aug 10, 3:52 PM EDT	Special Weather Statement	PHI	Berks, Carbon, Lehigh	23 min
Aug 10, 4:01 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Carbon, Chester, Lehigh, Montgomery, Northampton	44 min
Aug 10, 4:18 PM EDT	Areal Flood Advisory	PHI	Berks, Carbon, Lehigh	3 hr
Aug 10, 5:05 PM EDT	Special Weather Statement	PHI	Northampton	25 min
Aug 10, 5:09 PM EDT	Severe Thunderstorm Warning	PHI	Bucks, Montgomery, Philadelphia	51 min
Aug 10, 5:11 PM EDT	Special Weather Statement	PHI	Chester, Montgomery, Philadelphia	34 min
Aug 10, 5:40 PM EDT	Special Weather Statement	PHI	Chester	35 min
Aug 10, 5:58 PM EDT	Special Weather Statement	PHI	Philadelphia	32 min
Aug 10, 6:36 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester	39 min
Aug 10, 7:10 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Chester, Montgomery	65 min
Aug 10, 7:54 PM EDT	Severe Thunderstorm Warning Considerable damage threat	PHI	Chester	51 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.