Alert archive / New Jersey / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 497
The Storm Prediction Center issued this severe thunderstorm watch at Sep 13, 2021, 7:44 PM EDT for 6 counties in New Jersey; 6 counties in Pennsylvania. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 13, 2021, 7:44 PM EDT (23:44 UTC)
- Expired
- Sep 14, 2021, 12:12 AM EDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Morris County, NJ, Somerset County, NJ, Warren County, NJ, Bucks County, PA, Carbon County, PA, Lehigh County, PA, Luzerne County, PA, Monroe County, PA, Northampton County, PA
The radar
The Philadelphia radar (KDIX), 131 km from the middle of the area, began a volume at 23:46 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
- 5%
- 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
- 30%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
8 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 13, 8:16 PM EDT | Severe Thunderstorm Warning | PHI | Carbon, Monroe | 44 min |
| Sep 13, 8:28 PM EDT | Severe Thunderstorm Warning | BGM | Luzerne | 22 min |
| Sep 13, 8:41 PM EDT | Severe Thunderstorm Warning | PHI | Hunterdon, Warren | 49 min |
| Sep 13, 9:03 PM EDT | Severe Thunderstorm Warning | PHI | Hunterdon, Morris, Somerset, Warren | 57 min |
| Sep 13, 9:12 PM EDT | Flash Flood Warning | PHI | Hunterdon, Morris, Warren | 114 min |
| Sep 13, 9:21 PM EDT | Severe Thunderstorm Warning | PHI | Hunterdon, Somerset, Warren | 38 min |
| Sep 13, 9:34 PM EDT | Severe Thunderstorm Warning | PHI | Middlesex, Morris, Somerset | 38 min |
| Sep 13, 9:53 PM EDT | Severe Thunderstorm Warning | PHI | Mercer, Middlesex, Monmouth, Somerset | 52 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, 11.7 hours before the alert went out and 222 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
- 325 J/kg
- Mixed-layer CIN
- -257 J/kg
- Mixed-layer LCL
- 1152 m above ground
- 0-6 km bulk shear
- 61 kt
- 0-1 km storm-relative helicity
- 133 m²/s²
- 0-3 km storm-relative helicity
- 238 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.1
The text
As transmitted.
195 WWUS20 KWNS 132341 SEL7 SPC WW 132341 NJZ000-PAZ000-140500- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 497 NWS Storm Prediction Center Norman OK 745 PM EDT Mon Sep 13 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northern New Jersey Eastern Pennsylvania * Effective this Monday night and Tuesday morning from 745 PM until 100 AM EDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...A cluster of strong-severe thunderstorms upshear over north-central/northeastern PA may produce damaging/severe gusts and large hail as it moves across the watch area, before weakening near the Atlantic Coast. The severe thunderstorm watch area is approximately along and 25 statute miles north and south of a line from 40 miles west northwest of Allentown PA to 20 miles northeast of Trenton NJ. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU7). 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. && OTHER WATCH INFORMATION...CONTINUE...WW 496... 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. ...Edwards
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 12, 10:25 PM EDT | Severe Thunderstorm Watch | SPC | Erie | 4 hr |
| Sep 13, 12:26 AM EDT | Mesoscale Discussion | SPC | Susquehanna | 94 min |
| Sep 13, 4:11 PM EDT | Mesoscale Discussion | SPC | Cameron, Clinton, Elk, Erie, Forest, McKean and 2 more | 2 hr |
| Sep 13, 5:53 PM EDT | Severe Thunderstorm Watch | SPC | Cameron, Centre, Clarion, Clearfield, Clinton, Columbia and 14 more | 3 hr |
| Sep 13, 7:07 PM EDT | Mesoscale Discussion | SPC | Carbon, Centre, Clearfield, Columbia, Jefferson, Luzerne and 5 more | 113 min |
Nearby
Severe Thunderstorm Watches in New Jersey, 2021Severe Thunderstorm Watches in Pennsylvania, 2021Every severe thunderstorm watch 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.