Alert archive / Massachusetts / Mesoscale Discussions in 2021
Mesoscale Discussion 1756
The Storm Prediction Center issued this mesoscale discussion at Sep 15, 2021, 3:04 PM EDT for 8 counties in Massachusetts; Morris County, Passaic County, Sussex County, New Jersey; 5 counties in New York. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Sep 15, 2021, 3:04 PM EDT (19:04 UTC)
- Expired
- Sep 15, 2021, 5:00 PM EDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
Counties Berkshire County, MA, Essex County, MA, Franklin County, MA, Hampden County, MA, Hampshire County, MA, Middlesex County, MA, Suffolk County, MA, Worcester County, MA, Morris County, NJ, Passaic County, NJ, Sussex County, NJ, Dutchess County, NY, Orange County, NY, Putnam County, NY, Rockland County, NY, Westchester County, NY
The radar
The Brookhaven radar (KOKX), 119 km from the middle of the area, began a volume at 19:05 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
Albany, NY (KALY), launched 12:00Z, 7.1 hours before the alert went out and 115 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
- 856 J/kg
- Mixed-layer CIN
- -92 J/kg
- Mixed-layer LCL
- 766 m above ground
- 0-6 km bulk shear
- 51 kt
- 0-1 km storm-relative helicity
- 214 m²/s²
- 0-3 km storm-relative helicity
- 248 m²/s²
- Significant tornado parameter
- 0.7
- Supercell composite
- 6.3
The text
As transmitted.
172
ACUS11 KWNS 151904
SWOMCD
SPC MCD 151904
MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-152100-
Mesoscale Discussion 1756
NWS Storm Prediction Center Norman OK
0204 PM CDT Wed Sep 15 2021
Areas affected...portions of northern NJ...southern NY...CT...and MA
Concerning...Severe potential...Watch possible
Valid 151904Z - 152100Z
Probability of Watch Issuance...60 percent
SUMMARY...Severe thunderstorm potential is increasing across parts
of far northern NJ/southern NY into MA. A new severe thunderstorm
watch may be needed.
DISCUSSION...A narrow corridor of increasing severe potential exists
from far northern NJ into MA ahead of ongoing strong/severe
convection further to the north/northwest. This corridor has
experienced strong heating today, with temperatures mostly in the
mid to upper 80s amid 65-70 F dewpoints, yielding MLCAPE values
around 1500-2000 J/kg. Visible satellite shows a broad area of
agitated CU, with stronger vertical development across parts of
southern NY/northern NJ as well as near the MA/VT/NH border.
Stronger ascent will remain north of the area, so it is unclear if
any storms will develop ahead of the slowly east/northeastward
moving bands of convection further to the northwest. However, a
southeastward-advancing outflow boundary is noted from Delaware to
Rensselaer Counties in southeast NY and may provide enough focus for
additional development across/moving into the MCD area. Vertical
shear does decrease with southward extent across New England, but
effective shear magnitudes around 30-40 kts is more than sufficient
to maintain organized cells/clusters in a moderately unstable
airmass. As such, a severe threat could spread south of WW 501 and
WW 502 in the next couple of hours and a new watch may be needed.
..Leitman/Thompson.. 09/15/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GYX...BOX...OKX...ALY...PHI...BGM...
LAT...LON 42177357 42597287 42797205 42817080 42697055 42527055
42097149 41477303 40777453 40807474 40897494 41407473
42177357SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 15, 3:43 PM EDT | Severe Thunderstorm Watch | SPC | Capitol Planning Region, Northwest Hills Planning Region | 6 hr |
| Sep 15, 10:33 AM EDT | Mesoscale Discussion | SPC | Berkshire | 2 hr |
| Sep 15, 11:55 AM EDT | Severe Thunderstorm Watch | SPC | Berkshire | 8 hr |
| Sep 15, 4:38 PM EDT | Mesoscale Discussion | SPC | Berkshire, Franklin, Hampshire | 67 min |
Nearby
Mesoscale Discussions in Massachusetts, 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.