Tornadoes can happen here, but they are usually weak
If you live in the Midwest, you need to keep an eye on the sky for tornadoes. If you live in St. Helens, you might keep half an eye on cloud formations, because, yes, tornadoes can happen in Columbia County.
A small version of the meteorological phenomenon hit the Pittsburg Road area of St. Helens on Tuesday, Nov. 10.
In our part of the country, with a few exceptions, tornadoes are usually mild, causing some trees to tumble and roof shingles to fly.
"For the whole state of Oregon, we probably average something close to about two tornadoes a year," said David Elson, a meteorologist with the National Weather Service in Portland. "Most of those are pretty weak, but they do occur with some regularity."
In the Midwest, during tornado season, warm air can clash with cool air to produce ideal conditions for tornado formation. In this region of the country, the meteorological conditions differ.
"Our instability parameter is usually kind of weak compared to the Plains and the eastern part of the United States," Elson said.
In St. Helens, he explained, "This would have been a case where we had pretty good shear, a good change in the winds with height. We had a little bit of instability, just enough to get the showers going. Showers are a result of instability. So we had the instability, but it just wasn't terribly strong."
Unlike the Midwest, tornado formations in our neck of the woods can be hard to spot on radar.
"If it's (tornado) reasonably close to the radar, we can usually pick out the rotation, but it's usually not a very strong signature," Elson remarked.
While the St. Helens tornado was classified EF-0 in strength (the weakest on the Enhanced Fujita Scale), two EF-2 tornadoes have been recorded in Oregon in the past several years. A twister hit Aumsville on Dec. 14, 2010, causing damage. On Oct. 14, 2016, a twister cut a swath through the coastal town of Manzanita.
The granddaddy of all tornadoes in this region of the Northwest was the Vancouver Tornado of 1972. The EF-3 tornado, which hit April 5, killed six people, injured 300 and caused widespread damage in the area.
So, don't be surprised if you see a twister in the future.
"We don't get a lot of them," Elson said. "They're not always terribly strong, but we can get them."
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