How meteorologists determine whether tornadoes touch down

If it looked like a tornado and it twirled like a tornado, it was probably a tornado.

Determining whether a tornado touched down isn’t an exact science, but meteorologists pair radar data with debris patterns to determine whether funnel clouds actually touched down during storms.

Much of Maryland was under a tornado watch overnight Sunday, while Frederick, Carroll and Baltimore counties were under a tornado warning. Although it didn’t appear Monday morning that any tornadoes stretched to ground locally, the National Weather Service was still reviewing information it received from city and county emergency managers, 911 calls and reports from weather spotters to determine whether one touched down, weather service meteorologist Raymond Martin said.

Reviewing those reports and comparing them with radar data is the first step the National Weather Service takes when it comes to drawing conclusions about tornadoes. If the weather service thinks any areas were particularly hard-hit based on radar observations, it might call nearby spotters — volunteers who are trained to identify and describe severe weather — to find out what sort of damage they’re seeing.

If the radar information matches damage reports on the ground, the weather service sends one or two surveyors to examine an area for evidence that a tornado struck, Martin said. Telltale signs like twisted trees or debris scattered in multiple directions indicate a tornado touched down, Martin said.

“What they’re looking for are signs of any rotation,” Martin said.

The National Weather Service in Sterling, Virginia, doesn’t have any drones of its own, but occasionally surveyors will borrow them to take aerial images, too.

If debris patterns match the radar signature, that pairing provides strong evidence for meteorologists to declare a tornado touched down, Martin said.

It will likely be several days before the weather service indicates whether any tornadoes occurred Sunday night.

In Maryland, where tornadoes are rare, damage from tornadoes can be easy to confuse with damage from high winds. Gusty winds were expected to continue through Monday across the state.

“Depending on the strength of the storm and the development of the storm, there can be both, and sometimes it can be hard to separate out what was one and what was the other,” Martin said.

Generally, “straight-line winds” are more common in Maryland and can still cause severe damage.

“Tornadoes get all the attention because there are pretty to look at, they are pretty fascinating, they’re big huge vortexes milling across the plains,” Martin said. “Just because it was straight-line winds doesn’t mean it was less important or damaging.”

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