Alert archive / Massachusetts / Mesoscale Discussions in 2021

Mesoscale Discussion 1874

October 16, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Oct 16, 2021, 5:39 PM EDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Oct 16, 2021, 5:39 PM EDT (21:39 UTC)
Expired: Oct 16, 2021, 7:45 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Essex County, MA, Franklin County, MA, Hampden County, MA, Hampshire County, MA, Middlesex County, MA, Norfolk County, MA, Suffolk County, MA, Worcester County, MA, Hillsborough County, NH, Rockingham County, NH, Nassau County, NY, Suffolk County, NY, Kent County, RI, Providence County, RI, Washington County, RI

The radar

The Brookhaven radar (KOKX), 105 km from the middle of the area, began a volume at 21:39 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, 9.7 hours before the alert went out and 105 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1068 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 140 m²/s²
0-3 km storm-relative helicity: 174 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

077 
ACUS11 KWNS 162140
SWOMCD
SPC MCD 162139 
MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-VTZ000-162345-

Mesoscale Discussion 1874
NWS Storm Prediction Center Norman OK
0439 PM CDT Sat Oct 16 2021

Areas affected...Long Island and southern New England

Concerning...Severe potential...Watch unlikely 

Valid 162139Z - 162345Z

Probability of Watch Issuance...20 percent

SUMMARY...An isolated risk for damaging gusts may continue into the
early evening across Long Island and southern New England.

DISCUSSION...A broken squall line is oriented north-south from the
NY/MA/CT border into the greater NYC area as of 535pm EDT.  The
airmass ahead of the squall line over southern New England is
marginally unstable with temperatures in the lower 70s, and
dewpoints ranging from near 60 deg F in central MA to the mid 60s
near the coast.  The strength of the wind profile supports storm
organization but the deep-shear vector is largely parallel to the
squall line and this may limit the overall potential for more
intense downdrafts from developing.  Nonetheless, a conditional risk
for an isolated pocket or two of damaging gusts may continue as the
squall line moves across Long Island and southern New England over
the next couple of hours.  While it seems unlikely a severe
thunderstorm watch will be needed, convective trends will continue
to be monitored.

..Smith/Guyer.. 10/16/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BOX...OKX...ALY...

LAT...LON   40647375 41677317 42697278 43197165 42927077 42427080
            41017187 40557331 40647375

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 16, 12:35 PM EDT	Severe Thunderstorm Watch	SPC	Northwest Hills Planning Region	6 hr
Oct 16, 2:55 PM EDT	Mesoscale Discussion	SPC		95 min
Oct 16, 12:09 PM EDT	Mesoscale Discussion	SPC	Berkshire	2 hr
Oct 16, 11:06 AM EDT	Mesoscale Discussion	SPC	Broome, Chenango, Cortland, Delaware, Madison, Otsego and 2 more	114 min

Nearby

Mesoscale Discussions in Massachusetts, 2021 Mesoscale Discussions in Connecticut, 2021 Mesoscale Discussions in Rhode Island, 2021 Every 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.