The National Weather Service office in Portland said a tornado did indeed move through Battle Ground Monday, though there were no reports of major damage.

Witness videos and Doppler radar showed that it was a potential weak tornado, but meteorologists had to physically assess the damage before they knew its strength and its exact path.

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John Bumgardner with the National Weather Service told OPB Tuesday that storm surveyors head out to the scene with a giant book of directives that tells then what to look for and consider.

“You know, in the book it might say something like, ‘Well if you have a hardwood tree that snapped, and if it snapped this high up, then that corresponds to X wind speeds,’” he said. “And if it was a soft wood, like some kind of pine or spruce, then it was this wind speed. And the same thing for structural damage as well. So they’ll be looking for all of that and then referencing the book to make a final decision.”

Bumgardner said structural damage is assessed the same way. Wind speeds are almost always determined by damage, not by gusts measured in real time.

Tornadoes are becoming more common in the area, but usually they’re comparatively weak, according to Bumgardner.

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