Alert archive / Massachusetts / Tornado Watches in 2021

Tornado Watch 486

September 1, 20215 counties in Massachusetts; 5 counties in Rhode Island

The Storm Prediction Center issued this tornado watch at Sep 1, 2021, 11:37 PM EDT for 5 counties in Massachusetts; 5 counties in Rhode Island. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Sep 1, 2021, 11:37 PM EDT (03:37 UTC)
Expired: Sep 2, 2021, 7:00 AM EDT
In force: 7 hr
Issued by: the Storm Prediction Center
Strongest gust expected: 60 kt

Counties Barnstable County, MA, Bristol County, MA, Dukes County, MA, Nantucket County, MA, Plymouth County, MA, Bristol County, RI, Kent County, RI, Newport County, RI, Providence County, RI, Washington County, RI

The radar

The Boston radar (KBOX), 40 km from the middle of the area, began a volume at 03:40 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 30%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 5%
Ten or more severe hail reports: 5%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 30%

Warnings issued inside it

8 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Sep 1, 11:56 PM EDT	Tornado Warning	BOX	Barnstable, Dukes	49 min
Sep 2, 12:08 AM EDT	Flash Flood Warning	BOX	Barnstable, Dukes	8 hr
Sep 2, 12:22 AM EDT	Tornado Warning	BOX	Dukes	53 min
Sep 2, 12:45 AM EDT	Tornado Warning	BOX	Barnstable, Dukes	60 min
Sep 2, 1:15 AM EDT	Tornado Warning	BOX	Dukes	28 min
Sep 2, 1:56 AM EDT	Tornado Warning	BOX	Barnstable	26 min
Sep 2, 2:34 AM EDT	Flash Flood Warning Considerable damage threat	BOX	Bristol, Plymouth	6 hr
Sep 2, 5:26 AM EDT	Flash Flood Warning Considerable damage threat	BOX	Barnstable, Bristol, Dukes, Plymouth	3 hr

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Brookhaven, NY (KOKX), launched 00:00Z, 3.6 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.

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: 123 J/kg
Mixed-layer CIN: -47 J/kg
Mixed-layer LCL: 512 m above ground
0-6 km bulk shear: 53 kt
0-1 km storm-relative helicity: 279 m²/s²
0-3 km storm-relative helicity: 456 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.2

Open this sounding in Storm Lab

The text

As transmitted.

035 
WWUS20 KWNS 020332
SEL6  
SPC WW 020332
MAZ000-RIZ000-CWZ000-021100-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 486
NWS Storm Prediction Center Norman OK
1135 PM EDT Wed Sep 1 2021

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Southeast Massachusetts
  Rhode Island
  Coastal Waters

* Effective this Wednesday night and Thursday morning from 1135
  PM until 700 AM EDT.

* Primary threats include...
  A couple tornadoes possible
  Isolated damaging wind gusts to 70 mph possible

SUMMARY...A northward-advancing warm front near the coast in
addition to a moist air mass and strong low-level wind field will
support the possibility of a near-coastal/inland potential for
supercells with a brief tornado risk aside from convectively
enhanced winds.

The tornado watch area is approximately along and 40 statute miles
north and south of a line from 20 miles northwest of Block Island RI
to 25 miles east of Hyannis MA. For a complete depiction of the
watch see the associated watch outline update (WOUS64 KWNS WOU6).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Tornado Watch means conditions are favorable for
tornadoes and severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 484...WW 485...

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 0 inches. Extreme turbulence and surface wind
gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean
storm motion vector 23030.

...Guyer

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 1, 11:20 PM EDT	Mesoscale Discussion	SPC	Barnstable, Bristol, Dukes, Nantucket, Plymouth	85 min
Sep 2, 3:38 AM EDT	Mesoscale Discussion	SPC	Barnstable, Dukes, Nantucket	97 min

Nearby

Tornado Watches in Massachusetts, 2021 Tornado Watches in Rhode Island, 2021 Every tornado watch 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.