Alert archive / Massachusetts / Mesoscale Discussions in 2021
Mesoscale Discussion 1504
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 6:44 PM EDT for 10 counties in Massachusetts; 4 counties in New Hampshire; 5 counties in Rhode Island. It was in force for 61 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 6:44 PM EDT (22:44 UTC)
- Expired
- Aug 12, 2021, 7:45 PM EDT
- In force
- 61 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Bristol County, MA, Essex County, MA, Franklin County, MA, Hampden County, MA, Hampshire County, MA, Middlesex County, MA, Norfolk County, MA, Plymouth County, MA, Suffolk County, MA, Worcester County, MA, Cheshire County, NH, Hillsborough County, NH, Merrimack County, NH, Rockingham County, NH, Bristol County, RI, Kent County, RI, Newport County, RI, Providence County, RI, Washington County, RI
The radar
The Boston radar (KBOX), 51 km from the middle of the area, began a volume at 22:47 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, 10.7 hours before the alert went out and 174 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
- 278 J/kg
- Mixed-layer CIN
- -162 J/kg
- Mixed-layer LCL
- 1400 m above ground
- 0-6 km bulk shear
- 14 kt
- 0-1 km storm-relative helicity
- -82 m²/s²
- 0-3 km storm-relative helicity
- -47 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
711
ACUS11 KWNS 122245
SWOMCD
SPC MCD 122244
MAZ000-NHZ000-RIZ000-CTZ000-VTZ000-122345-
Mesoscale Discussion 1504
NWS Storm Prediction Center Norman OK
0544 PM CDT Thu Aug 12 2021
Areas affected...Southern New England
Concerning...Severe potential...Watch unlikely
Valid 122244Z - 122345Z
Probability of Watch Issuance...20 percent
SUMMARY...A cluster of thunderstorms west of Boston may pose a risk
for a few damaging wind gusts early this evening. Weakening of the
storms is ongoing and should continue limiting the threat.
DISCUSSION...KBOX radar data showed a line of thunderstorms along
the CT MA border moving east around 45 mph. SPC mesoanalysis
indicates around 2000 J/kg of MLCAPE is present but decreases
considerably near the Atlantic coast. Several measured severe wind
gusts near Springfield MA in the last hour suggest a few instances
of wind damage may still be possible with these storms as they track
toward the east early this evening. However, radar echo tops have
shown a considerable decrease in the last half hour as storms
approached the Boston and Providence metro regions. This suggests
storms are weakening rapidly as diurnal heating is diminishing. The
weakening trend is forecast to continue, but a few strong wind gusts
may still accompany thunderstorms through early evening.
..Lyons.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GYX...BOX...OKX...ALY...
LAT...LON 42027328 43197236 43397155 42987103 42677086 42217051
41827061 41467087 41297133 41307197 41547268 42027328SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 1:42 PM EDT | Severe Thunderstorm Watch | SPC | Berkshire | 6 hr |
| Aug 12, 3:50 PM EDT | Mesoscale Discussion | SPC | Essex, Franklin, Hampden, Hampshire, Middlesex, Norfolk and 2 more | 55 min |
Nearby
Mesoscale Discussions in Massachusetts, 2021Mesoscale Discussions in Rhode Island, 2021Mesoscale Discussions in New Hampshire, 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.