Pretty much anyone within an hour's drive to Puget Sound had quite the show last night, as a couple of very intense thunderstorms formed over the central Cascade mountains and then were steered right over the Tacoma-Seattle-Everett-Bremerton metro areas.
KOMO photographer Peter Mongillo went out to Mukilteo and then up to Monroe and shot some great video of the storms at a speed of 60 frames per second -- twice the speed of normal video recordings.
It allowed him to really slow down the video when the strikes hit, and it gave an amazing illustration of how lightning can travel across the sky:
First, here the Mukilteo/Whidbey Island movie:
And here it is from Monroe:
The intricate forks in the bolts are just the lightning's way of finding the path of least resistance to equalize its charge. Depending on what's going on in the air around the bolt, it's not always a straight line. Sort of like when you look at a traffic camera map and decide the side streets are faster than the freeway today.
Besides, lightning would be really boring if it were just straight lines!
Going the other way, here is sped up video of the storm as it passed over Hansville, courtesy of SkunkBayWeather.com
I've put some of the still shots from that video in the photo gallery here on this page.
Not your usual Seattle thunderstorm
Most storms around here we lovingly call "one-hit wonders" because the cells are usually lucky to only fire off a lightning strike or two -- certainly not the dazzling several-strike shows we saw Sunday night. Thunderstorms are rare here because you need warm, moist air on the ground and colder air aloft to allow that warm air to rise with authority.
Our "one-hit wonder" thunderstorms are usually because the air moving in aloft is so cold that it's enough of a difference to trigger a weak thunderstorm, even though we don't have the warm, moist air for fuel.
Our atmospheric flow here is almost always from the west/southwest, or northwest -- all coming off the cool Pacific Ocean waters that don't really give us that "warm, moist" component (warm air can hold more moisture than cold air, so we don't have that much potential for storms that way.) So we've got the moisture, not the warm.
Our second-most popular flow is from the east when we get thermal troughs, but that brings a very dry, continental air that dries even further as it goes over and sinks down our side of the Cascade mountains. So in that case, we've got the warm, but not the moisture. (This is also why it's very rarely warm and muggy here at the same time.)
But if we get a southerly flow, it's the rare hat trick of conditions that can bring our thunderstorms. For one, it's usually warmer to the south, so it'll push up warmer air that won't be cooled by the ocean nor dried out by sinking down the Cascades. And in this particular case, the monsoon season has started in the Desert Southwest, and this flow has tapped into some of that tropical moisture and moved in north into our area.
Now we've got the ingredients. The Cascades then provide lift to start the process of thunderstorm building, and the upper air flow takes it from there.
Sunday night, a storm formed around Mt. Rainier, and the upper level winds, while mainly south, had just a hint of southeast in it -- enough to nudge that storm west into the lowlands where it carved a path from Tacoma up north through West Seattle and into western Snohomish County and Whidbey Island, eventually going into the San Juans. A second set of storms hugged the Cascades and brought another show to the foothill communities.
It's a somewhat similar set up for Monday night, although it was pretty "lucky" that the storms made it that far west Sunday night and again, chances are low with greater threat of thunderstorms closer to the Cascades themselves.
As we get into Tuesday, the upper air flow will return more west/southwesterly which will cool us off a bit more, take away our warm/moist component and push any storms that do form in the mountains into Eastern Washington.