Sunday, June 17, 2012

Tornado or Straight-Line Winds: When Does the NWS Investigate?

After seeing firsthand the significant storm damage from powerful winds that occurred in and around TMF headquarters in St. Paul last Sunday night, we had cause to wonder: When does the National Weather Service decide to further investigate whether storm damage was caused by a tornado or straight-line winds? Obviously, to a property owner who’s looking at a tree over their car, the exact cause is not likely to be a pressing concern.

We took our question to Todd Krause, the warning coordination meteorologist at the Twin Cities National Weather Service in Chanhassen. Here is what he told us:

There are a couple reasons why we do surveys. One is if there is a great deal of interest (usually by the media and public) in what caused the damage (that is a subjective call on our part). We also will do a survey if we are trying to figure out scientifically what happened, so that we can review the radar data and other environmental clues and learn something for the next time. Even if we have had warnings in place, it is still important to learn something about what we’ve seen on radar etc.

Having said that, there will be times when we do not perform a survey every time there is damage somewhere. Sometimes staffing is such that we cannot spare anyone to go take a look. Or maybe more severe weather is anticipated and we need to remain at the office.  Or maybe somebody has provided pictures/video of a tornado or downburst and it is patently obviously what caused the damage. Or the scenario is obviously a certain type of damage (e.g. the Goodhue County storm damage on June 14 – see

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