August 28, 2010

A Change in the Sky

Yesterday from the Puget Sound Clean Air Agency Visibility Camera

Today from Dale Ireland's web cam

Notice that the sky has a very different look the past two days? Yes, there are clouds...but the clouds have a very different look...with the sky filled with cotton-ball, cumulus type clouds (see above two images). Some of the cumulus have grown into cumulonimbus with rain and lightning (see satellite picture below, particularly over the eastern Cascade slopes)

What has caused these changes? Destablization of the atmosphere. And what has caused that?--moving in of cool air aloft.

There really has been an amazing decline in the lower atmospheric temperatures this week. For example, at roughly 4000 ft...the height of Stevens Pass...the temperatures of the free atmosphere has declined 20F or more from the warm period of a few days ago. With the sun and surface heating still being relatively strong, and cool air moving in aloft, there develops a large change of temperature with height. This destablizes the atmosphere, producing convective mixing, like you see in a saucepan when you cook some oatmeal by turning on the burner.

Tomorrow will be like today, perhaps with more convection over the Cascades. And then things go downhill as a series of system move across the region. Looks like the coast and the southern half of western WA (and Oregon) will get seriously wet as the jet stream dives south of us. I would avoid hiking in the Oregon Cascades for a few days starting late tomorrow unless you are ready for wet stuff.

And keep in mind an important safety issue: the first real rain of the season often produces highly slippery conditions as all the oil that has accumulated during the summer emulsifies with the water. Nasty stuff.

In a future blog I will talk about the upcoming La Nina winter. Hint: this will be a better year to secure an annual ski pass.


  1. Your KUOW discussion on Fri. gave me chills Cliff! I immediately thought I've got to invest in that ski pass this year =) Can't wait to hear your future details.

    You absolutely should have a position in the mayors office..."already one mayor taken down by La Nina". HA - that was so funny.

  2. We were underneath t-storms today but it was all virga. Super dry airmass.

    Also, I noticed cumulus clouds and showers immediately east of the slopes use a trigger mechanism. Its peaks and ridges but mostly it's a convergence of the cool W mts breeze against a warm E valley breeze. Interesting to witness on a daily basis.

  3. Well I am not certain how much truth there is to this, but my cats are all bulking up really early this year. Guess its a good thing I buy it at Costco!

  4. Cliff... off topic a bit, but I think you'd enjoy seeing this... from last night (28th) I found this amazing satellite image of face in the clouds on the earth! Hurricane Danielle is the nose and posted it to my blog


  5. I've noticed over the last few weeks that when it's in the 60's & 70's there is a "coolness" in the air that I don't usually feel until mid to late September. Seems like the cool air is moving in a bit early this year! My tomatoes sure don't like it! I have a bunch of them but they aren't ripening! Can't wait to read your blog about the upcoming La Nina...Hope it's leans more on the "strong" side rather than just moderate...I love stormy, cool winters!

  6. I'm already gearing up for rain, wind, potential power outages etc. this late fall/winter. And I'm hoping we get some lowland snow! Bring on the La Nina post! (Oh, and my tomatoes are staying quite green as well....)

  7. The birds having been bulking up on seed and suet at my feeders for several weeks now. The Japanese Maples and Dogwood have started to turn pink in some spots. And there is just "something" in the air that feels different.

    My favorite season is on the way. And gosh, wasn't yesterday (Sat Aug 28) just spectacularly BEAUTIFUL?! If we could have a few more days like that to escort us into fall, I'd be quite content w/ a cold winter, thank you very much.

  8. Of course every year is different, but am I mistaken in thinking that we often have a dry and somewhat warmer than average fall during La NiƱa? Lovely September and first two weeks of October, then suddenly the firehose turns on.

  9. I am way off topic here but here goes. Everyone seems to lose interest in a big storm when it loses Tropical Storm status. Hurricane Danielle is poised to become a powerful extratropical storm. It looks like its going to hit sparsely inhabitied Greenland but I can't seem to find any info. Do you know of any good blogs or weather sites following these extratropiocal cyclones?

  10. When you post about La Nina in Seattle, could you please mention the local wind pattern in Seattle? Will we be getting cold winds from the north? Will we be getting the southwesterly storms? Most importantly, what are the the chances we'll get knock-down windstorms (through the I-5 corridor to Seattle)? Is there a greater chance, a lesser chance, or no data either way?
    Thanks (from the boaters).


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