Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2019

Severe Thunderstorm Warning 394, NWS Philadelphia/Mount Holly

September 11, 2019Chester County, Delaware County, Pennsylvania

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Sep 11, 2019, 9:02 PM EDT for Chester County, Delaware County, Pennsylvania. It was in force for 18 min. 1 report 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 11, 2019, 9:02 PM EDT (01:02 UTC)
Expired: Sep 11, 2019, 9:20 PM EDT
In force: 18 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

Counties Chester County, PA, Delaware County, PA

The radar

The Philadelphia radar (KDIX), 102 km from the middle of the area, began a volume at 01:05 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 11, 9:17 PM EDT	TSTM WND DMG	1 Wnw Westtown, PA	DOWNED POWER LINES NEAR THE INTERSECTION OF CONCORD ROAD AND WESTBOURNE ROAD. 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 00:00Z, 1.0 hours before the alert went out and 188 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: 122 J/kg
Mixed-layer CIN: -240 J/kg
Mixed-layer LCL: 1668 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 7 m²/s²
0-3 km storm-relative helicity: 29 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

780 
WUUS51 KPHI 120102
SVRPHI
PAC029-045-120145-
/O.NEW.KPHI.SV.W.0394.190912T0102Z-190912T0145Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
902 PM EDT Wed Sep 11 2019

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Central Chester County in southeastern Pennsylvania...
  Southwestern Delaware County in southeastern Pennsylvania...

* Until 945 PM EDT.

* At 902 PM EDT, a severe thunderstorm was located near Downingtown,
  or 7 miles west of West Chester, moving southeast at 25 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...
  West Chester, Chester, Coatesville, Westtown, Downingtown, Kennett
  Square, Cheyney, Elam, Marshallton, Lima, Chelsea,
  Lionville-Marchwood, Gradyville, Chester Township, Lionville,
  Concordville, Nether Providence Township, West Goshen, Brookhaven
  and Upland.

This includes Interstate 95 in Pennsylvania between mile markers 0
and 6.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4012 7566 3985 7533 3980 7541 3984 7550
      3984 7559 3982 7568 3978 7573 4005 7585
TIME...MOT...LOC 0102Z 327DEG 20KT 3997 7574 

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

Davis

1 follow-up statement

539 
WWUS51 KPHI 120120
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
920 PM EDT Wed Sep 11 2019

PAC029-045-120129-
/O.CAN.KPHI.SV.W.0394.000000T0000Z-190912T0145Z/
Chester PA-Delaware PA-
920 PM EDT Wed Sep 11 2019

...THE SEVERE THUNDERSTORM WARNING FOR CENTRAL CHESTER AND
SOUTHWESTERN 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, gusty winds are 
still possible with this thunderstorm.

LAT...LON 4012 7566 3985 7533 3980 7541 3984 7550
      3984 7559 3982 7568 3978 7573 4005 7585
TIME...MOT...LOC 0117Z 327DEG 20KT 3989 7567 

$$

Davis

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 11, 8:22 PM EDT	Special Weather Statement	PHI	Chester	23 min
Sep 11, 8:51 PM EDT	Special Weather Statement	PHI	Chester	39 min
Sep 11, 9:51 PM EDT	Special Weather Statement	PHI	Berks, Lehigh	24 min
Sep 11, 10:10 PM EDT	Severe Thunderstorm Warning	PHI	Berks, Lehigh, Montgomery	28 min
Sep 11, 10:37 PM EDT	Special Weather Statement	PHI	Bucks, Montgomery	38 min

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2019 Every severe thunderstorm warning in 2019

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.