What was that one clap wonder Friday night?

Area circled in red is the approximate location of the 5:10pm lightning strike. (All images courtesy Shoreline Area News)

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.

According to the following post from Carl Dinse, Weather Watcher from Shoreline Area News, 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 4:46pm 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 towards Seattle.

Then as the Puget Sound Convergence Zone drifted south, at just before 5:10pm a powerful cloud-to-ground-lightning bolt struck right near Interstate 5 and the 220th St 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 5:10pm.

To give you an idea what this convergence zone looked like this evening, below are two screen shots of the Doppler radar at the time. First image is the radar for 4:45pm, second image is the radar from 5:15pm.
Radar at 4:45 p.m. Friday.
Radar at 5:15 p.m. Friday.

Most of the rain from this event stayed north of the 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 the Shoreline Northridge (Echo Lake) weather station saw 0.01 inches from this event.

Anew storm was predicted to make its way into the region Saturday, with light rain and strong breezes gusting possibly up to 30-40mph.

Winds are supposed to taper off Sunday morning, with a relatively calm Sunday afternoon and evening. We have another rainmaker moving in on Monday. Extended forecast after Monday calls for a calmer Tuesday, still breezy but with showers. Wednesday through next Friday, however, looks sunny, clear, chilly and breezy at times. Highs near 50°F with lows in the mid-upper 30s later in the week.

— By Carl Dinse

 

  1. Oh yes! I virtually jumped, given the boom! My dog ran and was hiding for a while! And then came the thunder, and then the downpour! I took a video from that! Pretty scary for a while!

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