May 06, 2020

Lightning in the Cascade Foothills and Snow in the Mountains

Yesterday evening, western Washington had the visual treat of a magnificent lightning display along the western foothills of the Cascades.   A stunning picture by Sigma Sreedharan, illustrated the active thunderstorms that hit the region after roughly 5 PM

And the lightning strike map over the 24-h ending 1 AM today (Wednesday) shows the hundreds of lightning strikes west of the Cascade crest.

 Theses thunderstorms were associated with huge towering cumulonimbus clouds as illustrated by this wonderful cloud shot by Dr. Peter Benda, looking east from Bellevue.  Virtually mountains in the sky.

The huge cumulonimbus clouds were associated with the approach of an upper-level trough (low pressure), which caused upward motion (which helps initiate thunderstorms) and cooler air aloft (which helps to promote a large decline in temperature aloft, which in turn produces instability). Low level westerly winds pushed the unstable air up the western side of the Cascades, releasing the convection.

500 hPa (about 18,000 ft) heights, winds, and temperature (color shaded).

The visible satellite image at 7:01 PM clearly shows the bubbling thunderstorms on both sides of Seattle (the Kitsap had a storm as well).

Lots of lightning...but what about snow?

A fairly strong front (white arrow pointing to it) was lurking offshore yesterday afternoon (see visible image around 5 PM).  Behind the front was much cooler air, something made evident by the popcorn-looking instability clouds behind it (they are produced by cool air moving over warmer water).

Behind the front, the freezing level dropped to around 5000 ft (snow level around 4000 ft), but snow in the central Cascades got supercharged by the development of a Puget Sound convergence zone (which formed as the winds behind the front veered into a westerly direction).  The radar imagery this morning around 9 AM shows the convergence zone extending from Seattle eastward towards the Cascades--providing lots of precipitation and helping to drop the freezing level further (melting snow cools the air below).

The scene at Steven Pass at 10 AM this morning was, well, wintry and beautiful.

The cold air will soon be history and dry conditions, with temperatures zooming up into the lower 80s will be enjoyed by western WA residents this weekend.


  1. Last evening in Port Orchard we had a thunderstorm come through with the heaviest rain I've ever seen in my life. It was coming down in solid sheets. We got 0.23 inches in a little over five minutes. It was incredible. The temperature also instantly dropped 10 degrees.

    1. Here in the slightly south of downtown everett, we got a smaller version of what you had in Port Orchard....a couple of thunder rumbles, a couple of lightning flashes, followed by very heavy rain, that lasted for just a few minutes...Phooey!...I had just gotten comfy, looking outward to the west, ready to enjoy the weather show--and then it all stopped!...statistically, we only have around 7 lightning events each year, I do not even know if this mini-display would even count!

    2. At any randomly chosen location around here, that will happen only once every several years or so. At a randomly chosen location in the Rockies, the Midwest, or the East, that will happen several times a year.

  2. Cliff,

    I like thunderstorms with their lightning and rumbling thunder--the occasional thunder clap. It's great for lulling you to sleep when you are accustomed to it.

  3. Cliff, do you have any insight into the boom heard by many in the region? I've heard speculation including sonic boom, thunder, meteor, meth lab explosion, and weird weather thing.

  4. Cliff, we have reports of a bolide meteor over Brier just after 7 pm Wednesday, accompanied by a boom as it broke up near the stratopause. Do you have any resources that captured this object in flight?

  5. Where there any seismology readings? I'm not sure how legit this is but I found this:

  6. Love cumulonimbus clouds...great chieftains...think Chief Joseph of the Nez Perce whose birth name (take into account slight variations of English translations) was Thunder Rolling Down the Mountain.


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