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Not a tornado — a macroburst: Here's what caused storm damage in Baltimore, Harford counties last week

Not a tornado — a macroburst: Here's what caused storm damage in Baltimore, Harford counties last week
A large tree lies on the Hormes residence off Terra Bella Court in Fallston on Thursday morning. The tree was taken down during the line of storms that rolled through the area late Wednesday night. (Matt Button / The Aegis)

Maryland is in the midst of its biggest spate of tornadoes in years, but some storm damage last week didn’t come from a cyclone — but what are known as macrobursts.

The National Weather Service says macrobursts downed large tree limbs and snapped some telephone poles along two stretches in the Baltimore area Wednesday. They estimated that wind speeds approached 90 mph.

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What is a macroburst?

It’s a sustained pulse of severe straight-line winds caused by rapid downdraft of air within a tall storm cloud. The winds can reach speeds of more than 130 mph, last for five to 30 minutes, and extend across an area more than 2½ miles wide. (A microburst, on the other hand, involves winds approaching 170 mph over an area less than 2½ miles wide.)

To the casual observer, damage caused Wednesday in White Marsh and in the Baldwin and Fallston areas, along the border between Baltimore and Harford counties, appeared to be caused by a tornado.

In White Marsh, two wooden telephone poles snapped along Silver Spring Road, and many trees and large branches were downed across a 4-mile area extending into Nottingham.

In Baldwin and Fallston, large hardwood tree limbs fell, some onto homes, and the trunks of about a dozen pine trees snapped. And some residents captured images of what appeared to be a funnel cloud.

But weather service meteorologists determined it was macrobursts, not tornadoes, that caused the damage.

Tornadoes leave chaotic trails of damage, casting debris in all different angles. But macrobursts and microbursts leave their mark by tossing debris in a single direction.

In the White Marsh area, all observed tree damage fell toward the northeast, the weather service said. In Baldwin and Fallston, snapped trees all pointed toward the east.

And meteorologists said images of an ominous cloud in that area did not show a funnel cloud, but rather what appeared to be a roll cloud — a relatively rare tube-shaped cloud commonly mistaken for a tornado.

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