Wednesday, September 3, 20142:14 pm
Sorry, I was listening to Nickelback. But that question has often graced my mind when thinking about convergence zones. I’ve been wondering when we’d get a “zone to end all zones,” and this is the best one since the morning of December 18, 2008. I don’t think anything can top that one… I got 4-6 inches of snow and school was canceled. Our house also almost got struck by lightning around 5 a.m. It was bloody fantastic. That convergence zone represented the leading edge of the arctic air mass that settled in afterwards for nearly a week and wreaked havoc over the entire city.
|05:08 am PST, Thu 18 Dec 2008|
This zone, while not snowy and having quite as vicious lightning, had much heavier precipitation and much more lightning to go with it. Let’s take a look at some screenshots at certain times, and then some animations of the entire evolution of the convergence zone as a whole. All of these were retrieved from the UW Atmos Online Weather Data Archive.
|04:40 pm PDT, Tue 02 Sep 2014|
We started out with a strong squall line heading through Snohomish and Skagit Counties. It even had the signature of a “bow echo,” something commonly associated with very strong squall lines and mesoscale convective systems over the Great Plains, and something that is generally indicative of very high straight-line winds.
|05:25 pm PDT, Tue 02 Sep 2014|
45 minutes later, the squall line turned southeast and weakened.
|05:59 pm PDT, Tue 02 Sep 2014|
30 minutes later, we see more of a SW-to-NE oriented convergence zone begin to develop. The area of rain begins to broaden, and it continues to move southward. Northern Seattle is getting thunder and lightning.
|06:57 pm PDT, Tue 02 Sep 2014|
By 7, much of downtown has gotten thunder and lightning or is getting some at the moment. The real action, however, is further east. The zone becomes more east-west oriented.
|07:26 pm PDT, Tue 02 Sep 2014|
By now, only a few select places west of Lake Washington are getting hammered with precip. The vast majority of precipitation is falling east of the lake.
|08:57 pm PDT, Tue 02 Sep 2014|
|Retrieved from Seattle RainWatch|
Over 6 inches east of Maple Valley! Simply incredible. Meanwhile, places like Mountlake Terrace hardly got anything. That’s how thunderstorms work.