WeatherWatcher: Active weather, thunder, hail, cool and dry ahead

Friday, October 13, 2017

The last 24 hours has brought us significantly more active weather around here than we've been used to. Around 11:30pm Thursday night we had a thunderstorm move through the area, then early Friday morning a hail storm move through.

Initial reports were pointing at a Puget Sound Convergence zone as the cause of all this weather. However, after I reviewed radar images I've decided that Thursday night was just an unstable air mass moving through with a small scale thunderstorm squall line that happened to swing from west to east through Seattle, Shoreline, extendinh all the way up north past Burlington. You can click on any of these radar images for a full size view.

Radar image of Puget Sound Thursday night at 11:30PM Pacific.
Radar by National Weather Service

Friday morning's hail storm was a different story. There was a convergence zone, but it wasn't the typical one that forms from winds moving around the north and south sides of the Olympic mountain range. This one was formed by winds moving around Vancouver Island and converging west of Oak Harbor.

Below is a zoomed out image of Western Washington and Vancouver Island. I drew some arrows in red pointing in the direction winds were moving to create this type of convergence zone. You can see the perpendicular curved squall line northeast of Seattle at the eastern end of the convergence zone. That squall line was the hail storm.

Zoomed out radar image of Puget Sound Convergence Zone Friday at 8:00AM.
Radar by National Weather Service

This convergence started spitting out mini squall lines which made it southeast through Everett, Lynnwood, and south through Shoreline and Bothell. One of the early morning squall lines was dumping a significant amount of hail.

Below is a closer view of the radar image at 8:00am Friday morning showing the nice, long convergence zone formed between Vancouver Island and the Cascade mountains.
Puget Sound radar image Friday morning at 8:00AM.
Radar by National Weather Service

Forecast: Believe it or not, we have some cooler weather ahead for the weekend. We are looking at lows in the 30's and highs in the upper 40's to low 50's. Our first frost is possible especially in exposed or uncovered areas. It may also be a good time to think about wrapping up external plumbing and plumbing fixtures.

The good news about this weekend is we will be dry, and partly-mostly sunny during the days with patchy fog at night. If we do have our first frost, it should kill off a good portion of the summer end wasp population.

Our cool and dry period comes to an end late Monday or early Tuesday morning. The jet stream is going to be pointed right at us next week by Tuesday morning with our usual fall Pacific storm track to finish up the week.

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