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Here’s how the National Weather Service assesses tornadoes

Crews look at damage to determine wind speeds

ORLANDO, Fla. – Severe weather in Central Florida can happen pretty much anytime of the year, day or night.

During the winter, strong storms push through ahead of cold fronts. In the summer, sea breeze storms or tropical systems are to blame for our intense weather.

Within these severe weather events, tornadoes could form and cause significant damage.

Who decides if the damage is from an actual tornado?

That is where meteorologist from the National Weather Service come into play. Not only do they forecast the weather and send out warnings, they also go out and survey storm damage.

If a tornado is suspected either by the damage or eyewitness reports, a specialized team from the local National Weather Service office is deployed to investigate the area.

What information can they assess from the damage?

The survey team’s main goal is to gather enough data to reconstruct the lifespan of the tornado. This includes how long the tornado was on the ground (length path), the size of the twister and how strong it was (magnitude).

Tornadoes are categorized by the strength of their wind. Unlike hurricanes, tornadoes get their ranking by 3-second wind gusts compared to sustained winds in hurricanes.

Tornado intensity scale
Tornado intensity scale

How do they decide the magnitude and timing of the tornado?

When the crew arrives at the suspected tornado damage, they will conduct a full ground survey that could span several miles.

Along with their radar data, social media also helps them collect photos and videos from witnesses to get an idea of the timeline. They also have access to aerial footage, provided from news outlets, for an even more complete look at the area.

When it comes to determining the strength of the tornado, the team will look for the worst damage. Once that is found, the team will assign a damage indicator to the structure. Each one of these damage indicators has a description of the typical construction of the area.

EF scale damage indicators
EF scale damage indicators (NWS)

Once the indicator is selected, the team will then assign a degree of damage to the structure or object. The tornado evaluator will then make a judgement of the wind speeds that would've caused that specific damage, which will decide the official EF rating of the twister.

What tools do the meteorologist use in their survey?

The survey team is equipped with a few things that help them map out the tornado’s life cycle. This includes a GPS unit, a cellphone, a laptop with damage survey software, a digital camera, a map and a notebook.


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