Alert archive / New Jersey / Mesoscale Discussions in 2021
Mesoscale Discussion 1394
The Storm Prediction Center issued this mesoscale discussion at Jul 29, 2021, 7:09 PM EDT for 8 counties in New Jersey; Philadelphia County, Pennsylvania. It was in force for 96 min.
The area
The outline as issued.
The facts
- Issued
- Jul 29, 2021, 7:09 PM EDT (23:09 UTC)
- Expired
- Jul 29, 2021, 8:45 PM EDT
- In force
- 96 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 401
Counties Atlantic County, NJ, Burlington County, NJ, Camden County, NJ, Gloucester County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Ocean County, NJ, Philadelphia County, PA
The radar
The Philadelphia radar (KDIX), 13 km from the middle of the area, began a volume at 23:09 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
Brookhaven, NY (KOKX), launched 12:00Z, 11.2 hours before the alert went out and 175 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
- 54 J/kg
- Mixed-layer CIN
- -32 J/kg
- Mixed-layer LCL
- 823 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 65 m²/s²
- 0-3 km storm-relative helicity
- 127 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.1
The text
As transmitted.
013
ACUS11 KWNS 292310
SWOMCD
SPC MCD 292309
NJZ000-NYZ000-PAZ000-300045-
Mesoscale Discussion 1394
NWS Storm Prediction Center Norman OK
0609 PM CDT Thu Jul 29 2021
Areas affected...Far eastern Pennsylvania and central New Jersey
Concerning...Tornado Watch 401...
Valid 292309Z - 300045Z
The severe weather threat for Tornado Watch 401 continues.
SUMMARY...The tornado threat will continue for much of central New
Jersey for the next 1-2 hours as storms approach the coast.
DISCUSSION...Convection moving eastward out of far eastern PA into
central NJ continues to exhibit organized supercellular structure,
and at least one confirmed tornado has been noted with this activity
over the past hour. Recent surface observations across NJ show winds
have backed slightly to the south/southeast, which has augmented
low-level helicity over the region. This is captured well by the
KDIX VWP, which exhibits strong veering in the lowest 3 km. Recent
RAP soundings compare well to these observed trends and suggest
upwards of 150-200 m2/s2 effective SRH is in place across the
region. This wind profile, coupled with sufficient instability, will
continue to support a tornado threat as storms move towards the NJ
coast over the next 1-2 hours.
..Moore.. 07/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OKX...PHI...
LAT...LON 39977544 40457494 40617440 40487386 40217370 39797371
39227430 39367470 39637513 39977544SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 29, 2:23 PM EDT | Tornado Watch | SPC | Atlantic, Burlington, Camden, Cape May, Cumberland, Gloucester and 10 more | 8 hr |
| Jul 29, 4:26 PM EDT | Mesoscale Discussion | SPC | Burlington, Camden, Cumberland, Gloucester, Hunterdon, Mercer and 3 more | 94 min |
| Jul 29, 1:21 PM EDT | Mesoscale Discussion | SPC | Adams, Bedford, Blair, Cumberland, Dauphin, Franklin and 7 more | 114 min |
| Jul 29, 3:13 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Cambria, Clearfield and 6 more | 7 hr |
| Jul 29, 6:34 PM EDT | Mesoscale Discussion | SPC | Allegheny, Beaver, Fayette, Greene, Washington | 116 min |
Nearby
Mesoscale Discussions in New Jersey, 2021Mesoscale Discussions in Pennsylvania, 2021Every mesoscale discussion 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.