On Wednesday December 18th, an EF-2 rated tornado struck in Port Orchard, Washington near Seattle. The National Weather Service-Seattle tweeted that it was the strongest tornado to hit Washington state since 1986. The estimated peak winds were 120+ mph, and the roughly 250-300 yard wide tornado traversed the landscape for about 1.40 miles. While no one was injured, the tornado did cause damage to trees and structures. As news of this tornado spread, I suspected people might say that Washington state never gets tornadoes. The statement is "false" and a good opportunity to clear up two other myths as well.
According to a fact sheet issued by the National Weather Service, the state of Washington actually averages 2.5 tornadoes per year. The last tornado to impact western Washington (they are more common in the eastern part of the state) was on March 30th, 2017 in Monroe, Washington. These facts suggest that tornadoes are "rare" in Washington, but that they do happen. One of the state's worst tornadoes happened on April 5, 1972. A tornado ripped through Vancouver, Washington killing 6 people and injuring 300 including 70 children. Meteorologist James Spann tweeted statistics from the Seattle Times noting that the state of Washington has experienced 120 tornadoes over the period 1950 to 2016.
However, I want to emphasize a point that often gets lost in these discussions. Tornadoes are "rare" anywhere, relatively speaking. According to the NOAA's National Severe Storms Laboratory website,
About 1,200 tornadoes hit the U.S. yearly. Since official tornado records only date back to 1950, we do not know the actual average number of tornadoes that occur each year. Plus, tornado spotting and reporting methods have changed a lot over the last several decades.
Places typically associated with tornadoes get less activity than you think. According to a 2016 blog by Washington State University, Texas experiences approximately 146 twisters each year followed by Kansas (92) and Oklahoma (65). There are over 16 million thunderstorms globally each year and roughly 100,000 of them occur in the United States, according to NOAA. In the grand scheme of things, tornadic storms are "rare." Why does Washington state receive even less tornadic activity. The answer is basic meteorology and geography. Nic Lloyd and Linda Weiford wrote in WSU Insider blog,
In the Great Plains, the Midwest, the Mississippi Valley and the southern United States, the geography allows just this sort of thing to happen: warm, moist air flowing northward from the Gulf of Mexico interacts with cool air from the Rocky Mountains. But that’s not the case here, where we’re bound by the Pacific Ocean to the west and the Rockies to the east. A key ingredient that’s lacking is humidity, or water vapor in the atmosphere’s lower level.
Air emanating from the Gulf of Mexico may be warm and moist, but not the air moving off the chilly Pacific waters (see above).
Another myth that we can dispel is that a tornado anywhere can only happen during the warm season. People often think of "tornado season" as late Spring to Summer. This is certainly the peak time of activity for places like the Southern Plains. In the Northern Plains and upper Midwest, the peak activity tends to be in June and July. There are other regional variances, but the key point to remember is that tornadoes can happen at any time of the year. I noted earlier that Washington state experiences 2-3 tornadoes per year. However, 0.1 tornadoes per year happen in Washington during the month of December according to the National Weather Service-Seattle, which suggests that December tornadoes in Washington are extremely rare.
The final myth that often surfaces after an event like this is that tornadoes cannot hit cities. In this case, the tornado was about 15 miles from Seattle. I have long heard this myth. It is not true. I debunked this myth in a previous Forbes article. I wrote,
This myth likely emerged from the fact that tornadoes in major urban areas are relatively rare. Heck, tornadoes themselves are rare in themselves over the course of a given year, but their impact is potentially devastating so they get our attention. The reason they rarely hit a major city is that in the grand scheme of things, urban spaces are relatively small. Roughly 3% of the world's land surface is urban. The graphic above shows the relative amount of urban land cover in the United States. For illustrative purposes, imagine it was a dartboard. If you are an unskilled dart thrower, how often would you hit a city with a dart in 10 throws? Statistically, you are more likely not too.
