Alert archive / New Jersey / Severe Thunderstorm Watches in 2020

Severe Thunderstorm Watch 310

June 27, 202010 counties in New Jersey; 6 counties in Pennsylvania

The Storm Prediction Center issued this severe thunderstorm watch at Jun 27, 2020, 3:16 PM EDT for 10 counties in New Jersey; 6 counties in Pennsylvania. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Jun 27, 2020, 3:16 PM EDT (19:16 UTC)
Expired: Jun 27, 2020, 8:00 PM EDT
In force: 5 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

Counties Atlantic County, NJ, Burlington County, NJ, Camden County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Ocean County, NJ, Somerset County, NJ, Berks County, PA, Bucks County, PA, Chester County, PA, Delaware County, PA, Montgomery County, PA, Philadelphia County, PA

The radar

The Philadelphia radar (KDIX), 44 km from the middle of the area, began a volume at 19:16 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 SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 20%
One or more hailstones of 2 inches or more: 10%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

3 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jun 27, 3:37 PM EDT	Severe Thunderstorm Warning	PHI	Hunterdon, Mercer, Middlesex, Somerset, Warren	53 min
Jun 27, 4:17 PM EDT	Severe Thunderstorm Warning	PHI	Mercer, Middlesex, Monmouth, Ocean, Somerset	58 min
Jun 27, 5:12 PM EDT	Severe Thunderstorm Warning	PHI	Burlington, Mercer, Monmouth, Ocean	48 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Brookhaven, NY (KOKX), launched 12:00Z, 7.3 hours before the alert went out and 180 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: 1675 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: 63 m²/s²
0-3 km storm-relative helicity: 131 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

244 
WWUS20 KWNS 271914
SEL0  
SPC WW 271914
NJZ000-PAZ000-CWZ000-280000-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 310
NWS Storm Prediction Center Norman OK
315 PM EDT Sat Jun 27 2020

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Parts of central and southern New Jersey
  Extreme southeast Pennsylvania
  Coastal Waters

* Effective this Saturday afternoon and evening from 315 PM until
  800 PM EDT.

* Primary threats include...
  Scattered damaging wind gusts to 70 mph possible
  Isolated large hail events to 1.5 inches in diameter possible
  A tornado or two possible

SUMMARY...A small cluster of storms is expected to intensify while
moving east-southeastward from southeast Pennsylvania into New
Jersey this afternoon.  The storm environment will favor a mix of
short line segments and supercells capable of producing damaging
winds, though an isolated tornado and hail may occur with the
strongest storms.

The severe thunderstorm watch area is approximately along and 35
statute miles north and south of a line from 30 miles north
northwest of Philadelphia PA to 30 miles east southeast of Lakehurst
NJ. For a complete depiction of the watch see the associated watch
outline update (WOUS64 KWNS WOU0).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.

&&

AVIATION...A few severe thunderstorms with hail surface and aloft to
1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
29035.

...Thompson

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 27, 12:34 PM EDT	Mesoscale Discussion	SPC	Bergen, Burlington, Essex, Hudson, Hunterdon, Mercer and 9 more	2 hr
Jun 27, 4:15 PM EDT	Mesoscale Discussion	SPC	Hunterdon, Mercer, Middlesex, Monmouth, Ocean, Somerset	90 min
Jun 27, 5:30 PM EDT	Mesoscale Discussion	SPC	Cumberland, Salem	60 min
Jun 26, 11:15 PM EDT	Severe Thunderstorm Watch	SPC	Crawford, Erie	5 hr
Jun 27, 12:35 AM EDT	Mesoscale Discussion	SPC	Crawford, Erie, Mercer, Venango	115 min
Jun 27, 2:48 AM EDT	Mesoscale Discussion	SPC	Crawford, Mercer	57 min

Nearby

Severe Thunderstorm Watches in New Jersey, 2020 Severe Thunderstorm Watches in Pennsylvania, 2020 Every severe thunderstorm watch 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.