Weather Blog

What was with the "backwards thunderstorms"?

What was with the "backwards thunderstorms"?

Tuesday brought a strange sight to Western Washington -- not just the thunderstorms that popped up off the mountains, but the fact that they blew *to the west* toward Bellevue and through Seattle and into Kitsap County.

Typically, our weather moves west to east and on stormy days, we keep our eyes over Puget Sound for any approaching weather. What gives?

We can thank an area of low pressure to our southwest.  Here is a satellite image from Tuesday evening:

Air flows counterclockwise around a low pressure system, so you can see here how the low was pulling air back around from the east/southeast toward the west: (Hey, it's time for me to show off my "awesome" Photoshop skills again!)

As that air ran into the eastern slopes of the Cascades, the mountains provided lift to make the thunderstorms. Then the easterly winds carried those storms west across King and Snohomish County into Kitsap County.

Here are some time lapse videos of the day, courtesy of our usual contributors: Dr. Dale Ireland over in Silverdale and the UW Atmospheric Sciences Dept. Both cameras face west. Watch how the main upper air flow is moving southeast/east to west-ish.  But also notice the incredible wind shear going on with air flowing southerly and then, at times, northerly at the lower levels.

Here is the Silverdale one:

And here is UW:

I've already peeked ahead to part of Wednesday's time lapse from the UW, and it also shows some amazing wind shear going on in the morning. I'll highlight that Friday as part of the usual time lapse compilation.