Seattle thundersnow 'shocker'? Its lightning might have been caused by the Space Needle
SEATTLE -- The thundersnow event that rolled through Seattle Monday figuratively lit up social media as lightning literally lit up the Space Needle (twice!)
But some research suggests perhaps the Space Needle might not have been the victim of (at least) a pair of lightning bolts striking from the heavens. It turns out, the Space Needle might have been the one striking the clouds!
Thundersnow is a fairly rare event -- unlike major rain storms and severe weather cells that feature quite a bit of strong dynamics in clouds to create lightning, snow events usually don't have the wide change in temperatures or dynamics involved for frequent lightning.
But in the last few years -- and particularly a thundersnow event in Chicago in 2011 -- some have noticed when there is lightning during snow events, almost all of the lightning is centered on tall buildings. While that sounds feasible with regular thunderstorms, lightning detection equipment showed a dearth of other types of lightning -- such as cloud-to-air or cloud-to-cloud or cloud-to-ground-hitting-something-besides-a-super-tall-landmark.
According to this blog post by Weather Underground's Bob Henson, a few researchers went back in that Chicago storm and found 72 percent of the 282 lightning strikes detected in the storm were with about a half mile of a tall object -- in Chicago's case, mostly the Willis (formerly known as Sears) Tower and Trump Tower. (Yet the very tall Hancock Center was not hit.) And while there was heavy snow out over Lake Michigan as well, nary a lighting strike was detected there.
"In a typical summer storm, cloud-to-ground lightning will often strike the tallest object around--an isolated tree or house, perhaps--but the data suggest something else was going on in Chicago," Henson wrote in the blog. "When an tower is at least several hundred feet tall, the odds increase that the initial leader (the electrical charge that connects the thunderstorm cloud to the ground level object) will actually propagate from the top of the tower up to the cloud base, rather than the other way around. Just as a downward-propagating flash can branch out over its brief lifetime, striking several points on the ground, an upward-propagating flash can branch out as well."
Separate research projects have better studied this phenomenon called "self-initiated upward lightning," Henson said, and a "variety of evidence" suggests that's what was happening in that Chicago storm. These type of lightning apparently requires it to be snowing, with at least 18 mph winds at the top of the object to generate the electrical channel needed to reach the low cloud base.
In Seattle's case, we had three audible very loud lightning strikes near Seattle Center, with video proof that at least two struck the Needle. It's possible all three did. And with a strong Convergence Zone moving through, winds were certainly stronger than 18 mph atop the Needle:
So could it have been the Space Needle was the one sending the lightning bolts skyward instead of just being at the wrong place at the wrong time? Circumstantial evidence suggests it's a possibility!
Henson concludes in his blog: "In summary, tall towers don’t seem to be an absolute requirement for thundersnow, but they do appear to facilitate it in some ways that are only now becoming more apparent. The JGR study found that even objects less than 300 feet tall, such as cellphone towers and transmission lines in rural areas, can be enough to trigger thundersnow."