Weather Blog

Time lapse -- of the end of a heat wave

Time lapse -- of the end of a heat wave
Photo and caption By Reid Wolcott: "Marine push that arrived at 9:10pm at the north tip of Lake Washington. Winds were gusting over 50 kts and it was very challenging to even stand, let alone hold a camera on a tripod! A meteorologists/photographers dream!"

A bit of a different tack this Friday for the weather blog, where we normally do time lapse video.

But most of the week was sunny and boring... except for Thursday.  The epic crash of our heat wave made for some great photography.

I want to begin with series of photographs taken by the UW's Reid Wolcott, who is a graduate student and research assistant with the Atmospheric Sciences Department. (You might remember one of his photos from the Mt. Rainier lenticular cloud blog that went viral on e-mail. His was the one at sunset.)

He knew the marine push was coming, grabbed his camera and headed out to the northern tip of Lake Washington to see it roll on in.

You can see some his great photos on his Flickr site here

To get a good idea of what he went through, we can synch up his photographs to the minute-by-minute observations at the University of Washington Atmospheric Sciences Building.  That's a few miles to the south, but close enough. The temperature was likely about 83 degrees when the first sunset shot was taken. That had dropped to about 68 by the time he left.

Wow!

Here is the more traditional time lapse video from the UW building:

And how about this -- an apparent "Dust bow" taken by Mike Russell. Look closely and you can see a pink arc there in the middle of the photograph. I'm not sure if this is dust actually refracting light a bit like a rainbow, or if there was some rain in there doing the trick as some places did report light rain during the push. But it is interesting!

The marine push continued north and rolled up Vancouver Island, where the UW's Mark Albright says the swirling winds made an eddy in the fog along the northwestern coast:



So just what happened?

There is great debate in the local weather community over what exactly caused those strong winds across the Puget Sound area Thursday night.

We had two meteorological events occurring simultaneously -- a push of marine air rolling in off the coast, and a strong line of thunderstorms marching through northern Oregon and southern Washington.

Typically when we get a strong marine push, it can come with a period of gusty winds as the cool air replaces the hot air that was entrenched. On one hand, while we do get gusty winds, they're usually not 40-50 mph gusty and they're usually displaying sports-car like acceleration -- as in 0 to 50 in 5.5 seconds. Usually it's a building surge of wind.

On the other hand, it did have a rush of cool air behind it, as we'd expect in a marine push, and the pressure difference between the Seattle area and the coast was one of the highest in memory, so this would rate among the strongest marine pushes on record.

But there's also evidence we experienced what's called a "gust front." Typical of the massive thunderstorms in the Midwest, gust fronts are caused by extreme downdrafts out of the thunderclouds that race outward from the storms -- sort of like waves when you drop a stone in pond.

Some meteorologists contend visible-light satellite photos seemed to indicate a gust front as generated from those storms, but the problem is it got dark in the middle of the event, so we couldn’t really see it. (Infrared satellites would not pick up such nuances). And it's unknown whether a front would really survive that far to reach from Portland to Seattle.

There was also a surge of marine air moving east through the Strait of Juan de Fuca in the 8-9 p.m. hour, which would lean back toward marine push, but the surge was much weaker than you'd expect for such a great pressure difference.

So it's possible it was some sort of combination, or maybe they occurred at the same time, or maybe even the gust front helped trigger the marine push. Meteorologists will be poring over the observational data from around the region to see if we can solve the mystery and I'm sure someone will have a nice research paper out of it :)

Weather play by play

Here are some of the "play-by-plays" of the weather from that evening:

In Shelton, the marine air rolled by just before 7 p.m. on the tails of a 35-40 mph wind. The temperature plummeted from 88 degrees at 6 p.m. to 79 degrees at 7 p.m. and 63 at 8 p.m.

It hit Yelm around 7:30 with a gust of 54 mph.

A short time later, it rolled through Olympia with a 43 mph gust dropping the temperature from 85 at 7 p.m. to 72 at 8 p.m., and 66 by 9 p.m.

It hit Sea-Tac Airport just before 9 p.m. with the wind gusting to 36 mph blowing dust as well. The temperature went from 86 at 7:53 p.m. to 72 at 8:45 p.m.

University of Washington building at 8:53 p.m. -- 83 degrees. At 9:14 p.m.? 68 degrees.

Speaking of rapidly dropping, how would you like to dress in Forks today? They were at 90 degrees at noon, and by 7:38 p.m. it was 59 degrees. At 8:15 p.m. it blew through Port Angeles as I was on the phone with my Dad. At the start of the call, his home weather station was at 83. Ten minutes later, it was 68 and still dropping.

In fact, as a general rule, temperatures were near 90 across much of the region at around 6 p.m., and by 11 p.m., most of the region was in the low-mid 60s.

Have a great weekend!