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It was a one-clap thunder


November 14, 2019

Carl Dinse

Thunder, feel the thunder

Lightning and the thunder

– "Thunder," Imagine Dragons

Lights flickered. The cable flatlined. Then the boom, the thunderclap that shook homes, followed by drenching rain, all in a brief window on Friday, Nov. 15.

Carl Dinse of Shoreline gave an excellent explanation of what happened that should satisfy weather geeks, and we are all weather geeks when nature shakes our foundations. Carl, who publishes http://www.shorelineweather.com, wrote the following in the Shoreline Area News website (shorelineareanews.com). Some content has been edited.

Here's is Carl's story:

Were you in the area about 10 minutes after 5 p.m. Friday evening? If so, you probably didn't miss that very loud, ground shaking thunderclap we had.

Mother Nature is making up for two weeks of uneventful weather.

A strong Puget Sound convergence zone developed Friday evening behind the morning's cold front and light rain. The convergence zone crept its way south from Everett to Shoreline and east. This band was so strong, it created a weak rotation within a thunder cell just north of Shoreline and Lake Forest Park.

Storm cell rotation is usually the warning that a tornado may develop, but in the Puget Sound region tornados are extremely rare, so rotation in a cell is just a sign that we have an unusually strong thunderstorm on our hands.

Around 4:46 p.m., the power flickered as the first cloud-to-ground lightning bolt struck on the western edge of the Snohomish river valley in Everett.

The power surge from that lightning strike was reported in Everett, Seattle, Shoreline, and Mukilteo. I think it's a safe assumption that was because the lightning struck one of the main power transmission towers crossing the Snohomish river valley into Everett before feeding down toward Seattle.

Then as the Puget Sound Convergence Zone drifted south, at just before 5:10 p.m., a powerful cloud-to-ground-lightning bolt struck right near Interstate 5 and the 220th Street SW interchange in Mountlake Terrace.

The lightning strike was really brief, but so powerful it sounded like an explosion, followed by a long rumble. The thunder shook buildings through Shoreline and all the way up to Everett. The Shoreline Community Collage seismograph even detected shaking from the thunder at 5:10 p.m.

Most of the rain from this event stayed north of the King County border. Areas in Bothell and east received over an inch of rain in less than one hour. The rain gauge at the Shoreline-Richmond Beach weather station didn't have any measurable precipitation, whereas our Shoreline Northridge (Echo Lake) weather station saw 0.01 inches from this event.


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