Alert archive / Massachusetts / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 117, NWS Boston/Norton, MA

September 24, 2021Middlesex County, Worcester County, Massachusetts

NWS Boston/Norton, MA issued this severe thunderstorm warning at Sep 24, 2021, 11:11 AM EDT for Middlesex County, Worcester County, Massachusetts. It was in force for 22 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Sep 24, 2021, 11:11 AM EDT (15:11 UTC)
Expired: Sep 24, 2021, 11:33 AM EDT
In force: 22 min
Issued by: NWS Boston/Norton, MA
Area: Storm-based polygon
Tornado: Possible
Hail: 0.75 in
Wind: 60.0 mph

Counties Middlesex County, MA, Worcester County, MA

The radar

The Boston radar (KBOX), 83 km from the middle of the area, began a volume at 15:11 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

Gray, ME (KGYX), launched 12:00Z, 3.2 hours before the alert went out and 173 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: 249 J/kg
Mixed-layer CIN: -15 J/kg
Mixed-layer LCL: 537 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 144 m²/s²
0-3 km storm-relative helicity: 141 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.8

Open this sounding in Storm Lab

The text

As transmitted.

772 
WUUS51 KBOX 241511
SVRBOX
MAC017-027-241545-
/O.NEW.KBOX.SV.W.0117.210924T1511Z-210924T1545Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Boston/Norton MA
1111 AM EDT Fri Sep 24 2021

The National Weather Service in Boston/Norton has issued a

* Severe Thunderstorm Warning for...
  Northeastern Worcester County in central Massachusetts...
  North central Middlesex County in northeastern Massachusetts...

* Until 1145 AM EDT.

* At 1111 AM EDT, a severe thunderstorm was located over Ayer, or 10
  miles west of Chelmsford, moving north at 30 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Expect damage to trees and power lines.

* Locations impacted include...
  Chelmsford, Westford, Pepperell, Tyngsborough, Groton, Littleton,
  Lancaster, Ayer, Shirley, Harvard, Boxborough and Dunstable.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4270 7157 4270 7140 4269 7137 4248 7150
      4251 7166 4271 7162
TIME...MOT...LOC 1511Z 196DEG 28KT 4254 7155 

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Chai

1 follow-up statement

833 
WWUS51 KBOX 241533
SVSBOX

Severe Weather Statement
National Weather Service Boston/Norton MA
1133 AM EDT Fri Sep 24 2021

MAC017-027-241543-
/O.CAN.KBOX.SV.W.0117.000000T0000Z-210924T1545Z/
Worcester MA-Middlesex MA-
1133 AM EDT Fri Sep 24 2021

...THE SEVERE THUNDERSTORM WARNING FOR NORTHEASTERN WORCESTER AND
NORTH CENTRAL MIDDLESEX COUNTIES IS CANCELLED...
        
The storm which prompted the warning has weakened below severe
limits, and has exited the warned area. Therefore, the warning has
been cancelled.

LAT...LON 4270 7157 4270 7140 4269 7137 4248 7150
      4251 7166 4271 7162
TIME...MOT...LOC 1532Z 196DEG 28KT 4269 7149 

$$

Chai

The office that day

Everything else NWS Boston/Norton, MA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 24, 8:23 AM EDT	Severe Thunderstorm Warning	BOX	Hampshire, Worcester	15 min
Sep 24, 12:19 PM EDT	Special Marine Warning	BOX		56 min
Sep 24, 12:36 PM EDT	Special Weather Statement	BOX	Norfolk	54 min

Nearby

Severe Thunderstorm Warnings in Massachusetts, 2021 Every severe thunderstorm warning 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.