WeatherWatcher: Lightning and Thunder return to the skies again

Sunday, September 29, 2019

Convergence zone clouds over Shoreline.
Photo by Jan Hansen

Lightning and thunder returned to our skies for a third time this month on Friday, September 27, 2019. The atmosphere above us has been cooling rapidly over the past few weeks. This is due to an upper level jet stream pattern that has locked in place bringing us arctic air. If the upper level pattern continues to favor this configuration we may be in for a stormy and snowy winter.

Friday's storm was actually the result of a classic Puget Sound Convergence Zone event. We had cold air moving out of the Frasier river canyon from interior British Columbia colliding with mild moist air moving in from the southwest.

Here's the radar image at 5:30pm on Friday showing the developing convergence zone. The nice arc shape is actually the wave of colder air pushing south, creating the strong convection and precipitation band.

Radar image by the National Weather Service

Here's the image at 6:30pm as the lightning approached the Shoreline and Lake Forest Park area. You can see how the precipitation band is now well into downtown Seattle near Elliot Bay.

Radar image by the National Weather Service

Some of the more intense showers had some hail, as well, that briefly accumulated in lawns and on decks.
Photo by Jan Hansen

Forecast: This week should be relatively calm, but much cooler than we are used to. We're going to start the week with mostly sunny skies and clear nights, lows in the 30's, highs into the upper 50's. We may see our first frost this week. 

The sunny skies start to fade Wednesday afternoon with increasing clouds and a slight chance of rain Wednesday night. Thursday through the weekend we warm up a bit to lows in the 40's, highs near 60, and a chance of rain for the entire period.

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Anonymous,  September 30, 2019 at 11:02 AM  

Please Carl, could you remember my dog hates thunder? I work downtown and can't be at the Convergence Zone in Shoreline every time there is a weather event..

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