More Tornadoes Today; It IS “Tornado Season”

October 29, 2018

9:30pm Monday…

We had a bit less instability in the atmosphere overhead today, leading to the theory that the weather would be a bit calmer.  That more or less happened…until one, or more likely two, tornadoes briefly touched down west of the Cascades.  Once again these were very weak.  The first prompted a tornado warning about 3:40pm for far southern Marion County around Jefferson/Marion/Scio areas.  The tornado was seen on the ground briefly and we received a couple videos of the rotating funnel cloud too.  The NWS just happened to have a storm spotter class in Scio tonight, how convenient!  It turns out one sign was damaged and there was some tree damage as well.

The 2nd event was about one hour earlier.  A farmer a few miles north of Forest Grove saw a (likely) tornado’s wind touch down over his pond, pulling up water.  Then it damaged/destroyed several greenhouse structures; at that point he headed inside.  Here are some pics of that damage, the sky view is after it had moved off to the east.  Thanks to Jim Roofener for the pics:

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It was too dark for the NWS to conduct a storm survey on this one so we’ll find out if it was officially a tornado tomorrow.  UPDATE:  NWS confirmed on the morning of October 30th that it was an EF-0 tornado.

One question people ask me is why we typically don’t see these on radar?  Two reasons, one is that these “storms” are very weak.  Rotation and updrafts are nothing like we get with real tornadoes.  The other is distance from the radar site.  For example that Marion County tornado is about 70 miles from the radar site, so the lowest beam is at least 8,000′ overhead.  Much of the rotation could be below the beam and not able to be seen from that far away.

Tornado Why We Cant See Eugene

Of course the (likely but not confirmed) Forest Grove tornado was quite close to the Dixie Mountain radar site.  That said, I still didn’t see anything that stuck out.  That tells me it was very weak and even the bulk of that one may have been below the 2-3,000′ high radar beam.

Wayne Garcia came up to me and asked if this is a typical time for a tornado around here.  I’ve always know that the spring/fall seasons seem to be best.  So I pulled out the storm reports and started counting…

I checked all tornado reports in Western Oregon and 5 SW Washington counties (including Lewis County) from 1950 to this year.   I count 88 tornadoes, including the three (likely) this week.  Now check out the monthly breakdown

Tornado Season Stats

Yes, there sure is a tornado season, or maybe we should say “seasons”.  Spring and Fall.  They are rare in mid-summer and mid-winter.  October is sure a favored month isn’t it?  These are the seasons when we have the most vigorous “cold” showers and lots of mixing/instability. Interesting eh?

Now I call it “tornado season”, but those tornadoes often come in batches.  For example in Oregon, here are the last few years when we had a tornado in October:

2018, 2017, 2016, 2010, 2009, 2000.  So we can go numerous years without an October tornado; it’s not a yearly event.  But far less unusual than many of you think!

Chief Meteorologist Mark Nelsen