Alert archive / Massachusetts / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 81, NWS Boston/Norton, MA

July 17, 2021Middlesex County, Worcester County, Massachusetts

NWS Boston/Norton, MA issued this severe thunderstorm warning at Jul 17, 2021, 4:34 PM EDT for Middlesex County, Worcester County, Massachusetts. It was in force for 36 min. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Jul 17, 2021, 4:34 PM EDT (20:34 UTC)
Expired: Jul 17, 2021, 5:10 PM EDT
In force: 36 min
Issued by: NWS Boston/Norton, MA
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

Counties Middlesex County, MA, Worcester County, MA

The radar

The Boston radar (KBOX), 56 km from the middle of the area, began a volume at 20:35 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 was reported inside it

Time	Report	Where	Remark
Jul 17, 4:56 PM EDT	TSTM WND DMG	Worcester, MA	TREES AND WIRES DOWN ON HAVELOCK ROAD

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Brookhaven, NY (KOKX), launched 12:00Z, 8.6 hours before the alert went out and 180 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: 1203 J/kg
Mixed-layer CIN: -55 J/kg
Mixed-layer LCL: 1054 m above ground
0-6 km bulk shear: 24 kt
0-1 km storm-relative helicity: 35 m²/s²
0-3 km storm-relative helicity: 46 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.0

Open this sounding in Storm Lab

The text

As transmitted.

634 
WUUS51 KBOX 172034
SVRBOX
MAC017-027-172130-
/O.NEW.KBOX.SV.W.0081.210717T2034Z-210717T2130Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Boston/Norton MA
434 PM EDT Sat Jul 17 2021

The National Weather Service in Boston/Norton has issued a

* Severe Thunderstorm Warning for...
  Southeastern Worcester County in central Massachusetts...
  South central Middlesex County in northeastern Massachusetts...

* Until 530 PM EDT.

* At 434 PM EDT, a severe thunderstorm was located near Shrewsbury,
  moving northeast at 25 mph.

  HAZARD...60 mph wind gusts and quarter size hail.

  SOURCE...Radar indicated.

  IMPACT...Expect wind damage to trees and power lines. Minor hail 
           damage to vehicles is possible.

* Locations impacted include...
  Worcester, Framingham, Marlborough, Shrewsbury, Milford, Acton,
  Hudson, Westborough, Grafton, Sudbury, Holden, Ashland, Auburn,
  Northbridge, Hopkinton, Northborough, Oxford, Holliston, Millbury
  and Leicester.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4210 7186 4227 7194 4248 7149 4220 7138
TIME...MOT...LOC 2034Z 241DEG 21KT 4224 7175 

HAIL...1.00IN
WIND...60MPH
 
$$

Chai

1 follow-up statement

719 
WWUS51 KBOX 172110
SVSBOX

Severe Weather Statement
National Weather Service Boston/Norton MA
510 PM EDT Sat Jul 17 2021

MAC017-027-172120-
/O.CAN.KBOX.SV.W.0081.000000T0000Z-210717T2130Z/
Worcester MA-Middlesex MA-
510 PM EDT Sat Jul 17 2021

...THE SEVERE THUNDERSTORM WARNING FOR SOUTHEASTERN WORCESTER AND
SOUTH 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.  However heavy rain is still possible with this
thunderstorm.

LAT...LON 4210 7186 4227 7194 4248 7149 4220 7138
TIME...MOT...LOC 2109Z 241DEG 21KT 4234 7150 

$$

Chai

The office that day

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

Issued	Product	Office	Counties	Lasted
Jul 17, 2:37 PM EDT	Special Weather Statement	BOX	Franklin	38 min
Jul 17, 2:45 PM EDT	Special Weather Statement	BOX	Plymouth	45 min
Jul 17, 2:53 PM EDT	Special Weather Statement	BOX	Hampshire	52 min
Jul 17, 2:53 PM EDT	Severe Thunderstorm Warning	BOX	Bristol, Norfolk	52 min
Jul 17, 3:36 PM EDT	Areal Flood Warning	BOX	Bristol	114 min
Jul 17, 4:05 PM EDT	Severe Thunderstorm Warning	BOX	Worcester	34 min
Jul 17, 4:15 PM EDT	Severe Thunderstorm Warning	BOX	Hampden, Worcester	60 min
Jul 17, 4:38 PM EDT	Severe Thunderstorm Warning	BOX	Hampden, Hampshire	67 min
Jul 17, 4:48 PM EDT	Flash Flood Warning	BOX	Worcester	3 hr
Jul 17, 4:58 PM EDT	Flash Flood Warning	BOX	Hampden	2 hr
Jul 17, 5:10 PM EDT	Severe Thunderstorm Warning	BOX	Middlesex, Worcester	65 min
Jul 17, 5:34 PM EDT	Special Weather Statement	BOX	Hampshire	41 min
Jul 17, 5:35 PM EDT	Flash Flood Warning	BOX	Hampden, Hampshire	3 hr
Jul 17, 6:04 PM EDT	Flash Flood Warning	BOX	Hampden, Hampshire	3 hr
Jul 17, 6:05 PM EDT	Severe Thunderstorm Warning	BOX	Bristol	26 min
Jul 17, 7:49 PM EDT	Areal Flood Warning	BOX	Hampden, Worcester	116 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.