Alert archive / Pennsylvania / Severe Thunderstorm Warnings in 2020

Severe Thunderstorm Warning 240, NWS Philadelphia/Mount Holly

August 17, 2020Chester County, Delaware County, Pennsylvania; New Castle County, Delaware

NWS Philadelphia/Mount Holly issued this severe thunderstorm warning at Aug 17, 2020, 6:16 PM EDT for Chester County, Delaware County, Pennsylvania; New Castle County, Delaware. It was in force for 16 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 17, 2020, 6:16 PM EDT (22:16 UTC)
Expired: Aug 17, 2020, 6:32 PM EDT
In force: 16 min
Issued by: NWS Philadelphia/Mount Holly
Area: Storm-based polygon
Hail: 0.88 in
Wind: 60.0 mph

Counties New Castle County, DE, Chester County, PA, Delaware County, PA

The radar

The Philadelphia radar (KDIX), 116 km from the middle of the area, began a volume at 22:17 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.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 10.3 hours before the alert went out and 179 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: 9 J/kg
Mixed-layer CIN: -89 J/kg
Mixed-layer LCL: 685 m above ground
0-6 km bulk shear: 34 kt
0-1 km storm-relative helicity: 48 m²/s²
0-3 km storm-relative helicity: 54 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

772 
WUUS51 KPHI 172216
SVRPHI
DEC003-PAC029-045-172245-
/O.NEW.KPHI.SV.W.0240.200817T2216Z-200817T2245Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Mount Holly NJ
616 PM EDT Mon Aug 17 2020

The National Weather Service in Mount Holly NJ has issued a

* Severe Thunderstorm Warning for...
  Northwestern New Castle County in northern Delaware...
  Chester County in southeastern Pennsylvania...
  West central Delaware County in southeastern Pennsylvania...

* Until 645 PM EDT.

* At 615 PM EDT, severe thunderstorms were located along a line
  extending from near Glenmoore to Kemblesville, moving east at 25
  mph.

  HAZARD...60 mph wind gusts and nickel size hail.

  SOURCE...Radar indicated.

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

* Locations impacted include...
  Wilmington, West Chester, Phoenixville, Coatesville, Westtown,
  Downingtown, Elsmere, Kennett Square, Oxford, Parkesburg, West
  Grove, Cochranville, North Star, Marshallton, Pike Creek,
  Lionville-Marchwood, Ashland, Greenville, Glenmoore and Chester
  Springs.

This includes Pennsylvania Turnpike between mile markers 306 and 320.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

Protecting yourself from immediate threats to life and safety shall
take priority.  Whenever possible, as long as it does not cause
greater harm, all COVID-19 protective action guidance should be
followed.

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 4011 7589 4013 7551 3972 7557 3972 7602
TIME...MOT...LOC 2215Z 261DEG 21KT 4006 7575 3973 7583 

HAIL...0.88IN
WIND...60MPH
 
$$

Fitzsimmons

1 follow-up statement

823 
WWUS51 KPHI 172232
SVSPHI

Severe Weather Statement
National Weather Service Mount Holly NJ
632 PM EDT Mon Aug 17 2020

DEC003-PAC029-045-172241-
/O.CAN.KPHI.SV.W.0240.000000T0000Z-200817T2245Z/
New Castle DE-Chester PA-Delaware PA-
632 PM EDT Mon Aug 17 2020

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN NEW CASTLE...
CHESTER AND WEST CENTRAL DELAWARE COUNTIES IS CANCELLED...
            
The storms which prompted the warning have weakened below severe
limits, and no longer pose an immediate threat to life or property.
Therefore, the warning has been cancelled.  However gusty winds are
still possible with these thunderstorms.

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 4011 7589 4013 7551 3972 7557 3972 7602
TIME...MOT...LOC 2300Z 261DEG 21KT 4010 7541 3977 7549 

$$

Fitzsimmons

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 17, 5:08 AM EDT	Coastal Flood Advisory	PHI	Bucks, Delaware, Philadelphia	23 hr
Aug 17, 5:38 PM EDT	Severe Thunderstorm Warning	PHI	Chester	37 min
Aug 16, 10:52 PM EDT	Coastal Flood Statement	PHI	Sussex	4 hr
Aug 17, 10:44 AM EDT	Rip Current Statement	PHI	Sussex	11 hr

Nearby

Severe Thunderstorm Warnings in Pennsylvania, 2020 Severe Thunderstorm Warnings in Delaware, 2020 Every severe thunderstorm warning in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.