Alert archive / Massachusetts / Mesoscale Discussions in 2021
Mesoscale Discussion 2024
The Storm Prediction Center issued this mesoscale discussion at Dec 11, 2021, 9:49 PM EST for 9 counties in Massachusetts; 5 counties in New Hampshire; Windham County, Vermont. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Dec 11, 2021, 9:49 PM EST (02:49 UTC)
- Expired
- Dec 11, 2021, 11:45 PM EST
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Berkshire County, MA, Essex County, MA, Franklin County, MA, Hampden County, MA, Hampshire County, MA, Middlesex County, MA, Norfolk County, MA, Suffolk County, MA, Worcester County, MA, Cheshire County, NH, Hillsborough County, NH, Merrimack County, NH, Rockingham County, NH, Strafford County, NH, Windham County, VT
The radar
The Boston radar (KBOX), 101 km from the middle of the area, began a volume at 02:53 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
Albany, NY (KALY), launched 00:00Z, 2.8 hours before the alert went out and 151 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
- 956 m above ground
- 0-6 km bulk shear
- 95 kt
- 0-1 km storm-relative helicity
- 405 m²/s²
- 0-3 km storm-relative helicity
- 481 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
621
ACUS11 KWNS 120250
SWOMCD
SPC MCD 120249
MEZ000-MAZ000-NHZ000-VTZ000-NYZ000-120445-
Mesoscale Discussion 2024
NWS Storm Prediction Center Norman OK
0849 PM CST Sat Dec 11 2021
Areas affected...portions of Massachusetts...southern New Hampshire
Concerning...Severe potential...Watch unlikely
Valid 120249Z - 120445Z
Probability of Watch Issuance...5 percent
SUMMARY...A couple strong wind gusts may accompany a low-topped line
of showers progressing across portions of New England over the next
couple of hours. A WW issuance is not expected.
DISCUSSION...Very strong deep-layer ascent associated with a 70+ kt
LLJ, overspread by a 100-150 kt 300 mb jet streak, is contributing
to the forcing of a low-topped line of showers. Current MRMS mosaic
radar data shows 30 dBZ echoes struggling to reach 20 kft.
Nonetheless, the GYX 00Z observed sounding depicted 50 kt wind
speeds around 500 m AGL, suggesting that any efficient mechanical
downward momentum transport within the low-topped line of showers
may support continued strong wind gusts for the next few hours,
until the line moves off shore. Nonetheless, buoyancy is negligible
across New England. As such, organized/widespread severe winds seem
unlikely, and a WW issuance is not expected.
..Squitieri/Grams.. 12/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GYX...BOX...BTV...ALY...
LAT...LON 42287366 42847299 43257261 43357205 43447128 43407071
42957043 42387037 42147065 42087129 42047209 42077265
42147336 42287366Nearby
Mesoscale Discussions in Massachusetts, 2021Mesoscale Discussions in New Hampshire, 2021Mesoscale Discussions in Vermont, 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.