Alert archive / Connecticut / Mesoscale Discussions in 2021

Mesoscale Discussion 404

April 21, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Apr 21, 2021, 2:56 PM EDT for 4 states. It was in force for 94 min.

The area

The outline as issued.

The facts

Issued: Apr 21, 2021, 2:56 PM EDT (18:56 UTC)
Expired: Apr 21, 2021, 4:30 PM EDT
In force: 94 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 97

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

The radar

The Brookhaven radar (KOKX), 101 km from the middle of the area, began a volume at 18:59 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, 6.9 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.

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: 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

Open this sounding in Storm Lab

The text

As transmitted.

635 
ACUS11 KWNS 211857
SWOMCD
SPC MCD 211856 
MEZ000-MAZ000-NHZ000-RIZ000-CTZ000-NYZ000-VTZ000-212030-

Mesoscale Discussion 0404
NWS Storm Prediction Center Norman OK
0156 PM CDT Wed Apr 21 2021

Areas affected...CT...Most of MA...Southern NH

Concerning...Severe Thunderstorm Watch 97...

Valid 211856Z - 212030Z

The severe weather threat for Severe Thunderstorm Watch 97
continues.

SUMMARY...Threat for damaging wind gusts continues over southern New
England.

DISCUSSION...Low-topped convective line continues to move
eastward/northeastward at 40-45 kt into southern New England. Gusts
around 40-45 kt have been reported with this line thus far.
Downstream areas of western/central MA and CT are characterized by
temperatures in the mid 60s and steep low-level lapse rates (i.e. 7
to 8 deg C per km from 0-3 km). As such, the expectation is for
gusts of similar strength (i.e. 40 to 50 kt) to continue as the line
moves across western/central MA and CT over the next hour or so.

Some potential exists for the deep convection along the front to
reach into far southern New Hampshire, with an attendant threat for
a few damaging wind gusts.

..Mosier.. 04/21/2021

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

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

LAT...LON   41737357 42867250 43127063 41407181 40797240 40617364
            41737357

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 21, 11:49 AM EDT	Mesoscale Discussion	SPC		2 hr
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

Nearby

Mesoscale Discussions in Connecticut, 2021 Mesoscale Discussions in Massachusetts, 2021 Mesoscale Discussions in New Hampshire, 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.