EF0 tornado, Dennis, Massachusetts, September 1, 2021

1. EF065 to 85 mphthis tornado

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF0

Date

September 1, 2021

Touchdown

1:30 AM EDT (05:30 UTC)

Lifted

1:31 AM EDT (05:31 UTC)

On the ground

1 minutes

Path length

0.1 miles (0.2 km)

Path width

15 yards (14 m)

Deaths

0

Injuries

0

Property damage

$15,000

County

Barnstable County

Touchdown point

41.741, -70.213

Lift-off point

41.743, -70.213

Record number

2109012330-01

On Sept. 1, Tropical Depression Ida tracked northeasward from the central Appalachians and arrived in southern New England late in the day as a remnant low. The low moved rather swiftly across southern New England, reaching the coastal waters east of Massachusetts by 7 AM EDT on Sept. 2. One to three inches of rain fell in northwest Massachusetts, but heavy amounts of 4.0 to 6.5 inches fell south of the Mass Pike, with the heaviest amounts, near 7 inches, in the upper portion of Cape Cod. The most intense rain fell from the evening on the 1st to the early morning on the 2nd. There was widespread street flooding and some flash flooding. In addition, a brief tornado touched down in Dennis, MA (on Cape Cod) during the overnight hours.

A weak tornado briefly touched down at 130 AM in Dennis early in the morning and lasted for less than one minute. Damage was observed near the intersection of East Bay View Road and Wampanoag Trail. One home sustained damage when a window of a sun porch was blown in and others on an adjacent side were blown out. Outside patio furniture was lofted and landed across the street. Another house across the street had shingles blown off the roof in the opposite direction from other damage that was observed. Three large oak trees in the area also were blown down. One resident received the tornado warning prior to 1 AM and was able to seek shelter in the basement. The estimated maximum wind speed was 75 mph.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

45 minutes of warning. NWS BOX issued a tornado warning for this county at 04:45 UTC, 45 minutes before the tornado touched down, in force until 05:45 UTC.

The county was under a tornado watch, issued at 03:37 UTC and running to 11:00 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 00:59 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Hyannis/Polando Field (HYA), 10 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Boston radar (KBOX), 80 km away, was scanning. The volume nearest the touchdown began at 05:27 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2021 tornado in MassachusettsEvery tornado in Massachusetts since 1950Warnings in force in Massachusetts nowThe forecast where you are

10 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.