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


9 Replies to “What was that one clap wonder Friday night?”

  1. Ah hah! Mystery solved. I live just north of the “epicenter” of the lightning strike and the thunder shook my house and scared my poor dogs (and me). Thanks for the explanation!


  2. I was walking at dusk with my grandkids and my timid greyhound. The dog was scared to death, but the kids just said, “Was that thunder?”


    1. The map indicates the approximate area. I don’t have more specific details. I have not heard if there was any visible damage.


  3. We live near the center of your red circle. The thunderclap was loud enough to set off a couple of car alarms, followed by a deluge of rain. Unusual for the PNW, no big deal if you come from East of the Rockies. Nice article!


  4. And I got caught up in the surge of rain water that smashed around on the south side of the Value Village site (on Hwy 99.) The thunder was low and very loud and the water was about 3 feet high in the Value Village spot. I had to really get my car though the water at Value Village, and it was a chore.


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