Alert archive / New Jersey / Mesoscale Discussions in 2021
Mesoscale Discussion 402
The Storm Prediction Center issued this mesoscale discussion at Apr 21, 2021, 11:49 AM EDT for 4 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 21, 2021, 11:49 AM EDT (15:49 UTC)
- Expired
- Apr 21, 2021, 2:15 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
All 39 counties
Berkshire County, MA, Franklin County, MA, Hampden County, MA, Hampshire County, MA, Worcester County, MA, Bergen County, NJ, Burlington County, NJ, Camden County, NJ, Essex County, NJ, Hudson County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Morris County, NJ, Ocean County, NJ, Passaic County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Bronx County, NY, Columbia County, NY, Dutchess County, NY, Greene County, NY, Kings County, NY, Nassau County, NY, New York County, NY, Orange County, NY, Putnam County, NY, Queens County, NY, Rensselaer County, NY, Richmond County, NY, Rockland County, NY, Ulster County, NY, Westchester County, NY, Bucks County, PA, Delaware County, PA, Philadelphia County, PA
The radar
The Brookhaven radar (KOKX), 101 km from the middle of the area, began a volume at 15:49 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Brookhaven, NY (KOKX), launched 12:00Z, 3.8 hours before the alert went out and 101 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1427 m above ground
- 0-6 km bulk shear
- 37 kt
- 0-1 km storm-relative helicity
- 206 m²/s²
- 0-3 km storm-relative helicity
- 201 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
959
ACUS11 KWNS 211550
SWOMCD
SPC MCD 211549
MAZ000-CTZ000-NYZ000-NHZ000-VTZ000-NJZ000-PAZ000-211815-
Mesoscale Discussion 0402
NWS Storm Prediction Center Norman OK
1049 AM CDT Wed Apr 21 2021
Areas affected...Western MA...NY Hudson Valley...Western/Central
Long Island...Western CT...NJ
Concerning...Severe potential...Watch possible
Valid 211549Z - 211815Z
Probability of Watch Issuance...60 percent
SUMMARY...Thunderstorm development is anticipated over the next hour
or two along a cold front progressing through the Northeast.
Damaging wind gusts are possible with these storms and trends are
being monitored for possible Severe Thunderstorm Watch issuance.
DISCUSSION...Recent surface analysis places a low near the NY/NJ/PA
border intersection. A warm front extends eastward/northeastward
from this low across southern NY through western MA and off the far
southern ME coast. This low is embedded within a broad area of low
pressure preceding a strong frontal surge attendant to a shortwave
moving into western PA/NY. This low is expected to deepen over the
next few hours ahead of the front while the warm front lifts
northward. As a result, temperatures in the low to mid 60s will
likely be in place ahead of the front from western MA through
central NJ. Low-level moisture will be modest (i.e. in upper 40s/low
50s) but the steep low and mid-level lapse rates will foster modest
buoyancy.
Expectation is that deeper convection will begin developing along
the front during the next hour or two before then moving quickly
eastward across the region. Previously mentioned steep low-level
lapse rates coupled with deep convection and strengthening low to
mid-level flow will result in the potential for damaging wind gusts
as the storms move through. Storm coverage may be high enough to
merit watch issuance and convective trends are being monitored
closely.
..Mosier/Guyer.. 04/21/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GYX...BOX...OKX...ALY...PHI...BGM...
LAT...LON 42007464 42827370 42997248 42527173 40567305 40117347
39677459 39897543 40937512 42007464SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 21, 12:28 PM EDT | Severe Thunderstorm Watch | SPC | Greater Bridgeport Planning Region, Capitol Planning Region, Northwest Hills Planning Region, Lower Connecticut River Valley Planning Region, Naugatuck Valley Planning Region, Southeastern Connecticut Planning Region and 1 more | 5 hr |
| Apr 21, 2:56 PM EDT | Mesoscale Discussion | SPC | 94 min | |
| Apr 21, 12:22 PM EDT | Mesoscale Discussion | SPC | Cape May, Cumberland, Salem | 113 min |
Nearby
Mesoscale Discussions in New Jersey, 2021Mesoscale Discussions in New York, 2021Mesoscale Discussions in Connecticut, 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.