This morning’s tornado in Concord, explained

An early morning storm brought a tornado to the area, and winds were as high as 100 miles per hour.

Four-year-old Stella Marquis clutched "Puppy," her stuffed animal, and looked around as her mother and their neighbors discussed the storm damage. –Dina Rudick/Globe Staff

A cold front — and an associated line of showers and storms — swept through the area early Monday morning, bringing briefly torrential rain to many areas in Massachusetts. This severe weather did spawn a tornado inside an area of very strong winds.

The strongest part of the line of storms was in the Marlborough to Concord area, where wind damage was evident. Several residents awoke to downed trees and power lines, the result of the strong winds. Additionally the power was out for hundreds of families.

The National Weather Service spent time today evaluating the damage to determine if the strong winds were caused by a tornado or downburst. We now know the damage was the result of an F-1 tornado, with winds of about 100 miles per hour.

The tornado was on the ground for about half a mile, and was 400 yards wide.

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According to the National Weather Service out of Taunton, the tornado touched down near Cambridge Turnpike around 3:20 a.m. EDT before heading toward the northeast. Most of the damage was “concentrated near Alcott and Independence Roads where trees were uprooted or had the tops sheared off at the top.”

“It was evident that trees were blown down in opposite directions,” according to the National Weather Service. “Several houses sustained damage to roof shingles. Damage was more spotty in nature farther northeast where it is suspected the tornado lifted after only a few minutes.”

The reason why people need to physically evaluate the fallen trees, power lines and other damage is to see how the damage occurred and the pattern it takes. If the damage is strewn in more of a circular pattern it was caused by a tornado; damage where the debris has fallen in one direction means the strong winds were likely caused by a downburst or microburst.

The pattern of damage from thunderstorms helps experts determine the exact cause.
The pattern of damage from thunderstorms helps experts determine the exact cause. —NOAA

Early this morning a tornado warning was issued by the National Weather Service in Boston for parts of Middlesex County near the strongest part of a thunderstorm in that area.   The reason a tornado warning was issued is that there was rotation within a thunderstorm.

Crews were out since the pre-dawn hours cleaning up downed trees and fallen power lines on Independence and Alcott Roads in Concord, MA on Monday morning, August, 22, 2016. Severe weather moved through eastern Massachusetts in the early hours Monday, leaving damage in its wake.
Crews were out since the pre-dawn hours cleaning up downed trees and fallen power lines on Independence and Alcott Roads in Concord, MA on Monday morning, August, 22, 2016. —Dina Rudick/Globe Staff
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The radar image below is measuring the velocity of the winds. The red colors represent winds moving away from the radar site in Taunton, and the green colors represent winds moving toward the same site in Taunton.

If there are winds moving toward and away from the radar site in a location and the winds are shaped in this circular pattern, it represents rotation.

The reason verification is needed after the storm occurs is because the radar sees rotation within the thunderstorm, not at the ground. The radar beam from the site in Taunton is pointed into the clouds.  It can’t be pointed at the ground because if it was it would be blocked by trees and buildings.

Doppler radars are the best tool to evaluate for possible tornadoes, other than actually seeing them.

There have been recent tornadoes in Massachusetts. On the anniversary of the Revere tornado this year, I wrote a piece about tornadoes and their frequency in the area.

On average, one tornado occurs in the state of Massachusetts each year, but some years there are more and some there are none.

I don’t see any more thunderstorms in the forecast for the next several days and there’s a good chance most of us won’t see even a drop of rain the rest of the month.

Doug Morrill cleared brush from around his 3-month-old (and smashed) Mercedes.
Doug Morrill cleared brush from around his 3-month-old (and smashed) Mercedes. “I wouldn’t have waxed it three days ago,” said Morrill of his new car. —Dina Rudick/Globe Staff
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