August 09, 2010

Diablo Winds in the North Cascades and the Upcoming Heat Wave!

An green-blue mountain lake with towering mountains, snowfields and glaciers, as well as a fascinating meteorology--the is what I found during a pleasant stay this weekend at the North Cascade Institute, where I was one of the instructors for their Naturalist Weekend Retreat. The location of this beautiful facility is on Diablo Lake (see maps above and below), behind City Light's Diablo Dam. A very pleasant place to take environmentally oriented classes or to use as a base for exploring the North Cascades.

The lake (see picture below) has a green-bluish tinge due to the very fine particles produced by the surrounding glaciers (glacial flour). Why greenish blue? Why is the sky blue? A similar reason--what is known as Rayleigh scattering of visible light. Very fine particles scatter short wavelengths (like blue or green) far more than longer wavelengths (like red or yellow). Thus the shorter wavelengths are scattered back to your eye producing the bluish or greenish tint.

Some of the most exceptional meteorological features of this location are the diurnal (daily) winds. Nearly every day in summer the winds pick up on the lake around noon, with the flow accelerating up to 12-25 mph, often producing whitecaps. The wind is from the west, flowing directly up the Skagit River valley (see map above). During my stay I noted a strong correlation between this westerly wind and the pressure difference across the Cascades; when eastern Washington pressure fell relative to the west, the winds accelerated. Thus, the winds appeared to be gap winds, which are roughly proportional to the pressure difference across the gap. The interesting thing for me, is although the gap is very clear to the west (the Skagit River Valley), to the immediate east there is considerable blocking terrain until one gets to Mazama. But clearly the air rushing up the Skagit is going somewhere as it pushes to the east. Since the pressure difference increases during the day (eastern Washington heats up, air there becomes less dense, and thus the pressure falls), the wind strengthened late morning into the afternoon.

Want to see a video of the winds that I took from an overlook above the eastern side of Diablo Lake? Check this out:

Those trees are permanently deformed by the strong westerly winds!

Another interesting feature includes the rainfall and clouds. There is a very large precipitation gradient across this area. At Diablo and Ross dams they typically get about 57 inches a year, yet at Newhalem, the City Light company town a few miles to the west, there is usually about 79 inches. And far more in the mountains to the west. You can frequently see the clouds breaking to the east of the mountains west of Diablo Dam (see my marked up picture). That really makes that area far less cloudy than the windward slopes of the north Cascades.

The basin surrounding Diablo Lake is home to an extraordinary number of glaciers and of course State Route 20 is famous for its wintertime snow closures. It only has been able to stay open for one winter- the amazingly dry winter of 1976-1977.

Finally, let me talk about current weather. We had some showers and clouds today, but don't worry...a BIG change is coming later this week. Sun and warmth will return on Friday and expect the 80s this weekend. Don't listen to those who tell you summer is is not.


  1. As a graduate student with NCI, living on the edge of Diablo, I looked forward to the crazy afternoon winds. It's exciting to have a clear explanation as to why they happen! I wish I could have come this weekend, I'm sure it was fantastic

  2. It looks as if that tree ablowin' in the wind is moderately flagged. That is, the branches on the windward side are frequently broken off so the tree presents a lop-sided appearance. This usually occurs at high altitudes were strong winds are persistently from one direction.

  3. I was so excited to see this post! My family and I just got back from camping on Gorge Lake and we were a little blown away by the winds (pun intended). So neat to know the source, one of the reasons I love your blog! Thanks :)

  4. I'm not sure Mazama is the destination of that wind. I kayaked on Ross Lake recently, and the same reliable wind blows S-N up that valley - I wonder if the air's being drawn into inland BC?

  5. There is a wind in Northern California up in Butte County. Like clockwork in the summer at the Jarbo CDF in station in Jarbo Gap around 0500 a strong down canyon wind blows. It usually fallows a hot day in the Sacramento Valley where there are up canyon winds through out the afternoon.

  6. I've experienced the same afternoon phenomenon on Fish Lake -just East of Lake Wenatchee. The first couple fishing trips ended with a long wet haul back due to whitecaps breaking over the bow of our small boat. The warm Eastern WA sunshine quickly dried us out though.

  7. Hey Cliff, did you see this video of a storm rolling in from Finland? It's pretty cool. Can you write a little bit about it?

  8. Loved seeing the wind over Diablo lake. I grew up there-- what a lovely place to live! Thanks for the memories. :)

  9. We had some showers and clouds today, but don't worry...a BIG change is coming later this week. Sun and warmth will return on Friday
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