April 17, 2011

Unstable Air and the Northwest Weather Workshop

Although the cold air that has been moving in aloft these days may have its down sides for gardening and some outdoor activities, there IS a silver lining to the situation....very nice cumulus and cumulonimbus clouds for viewing (an example shown above from the Puget Sound Clean Air Agency "Visibility Cam."

Believe it or not, the sun is actually getting fairly strong (the sun's strength today was the same as late August!!!), so the surface is getting quite a bit of solar radiation when the sky opens up. And the day is quite long now (like late August!).

Now the result of cold air aloft, but warming at the surface is that a large difference in temperature develops with height. In the business, we call that a large temperature lapse rate.

So why do we care about this? Well, when the lapse rate gets large enough the atmosphere can get unstable and it starts to convect. This is exactly what happens when you make hot cereal by the way (and if you don't eat hot cereal, you should, it is good for you). You put the a saucepan on the burner and when the vertical lapse rate because large enough the cereal starts to convect....some moving up and some moving down. Add some brown sugar...

Or you can see convection take place in a Lava Lamp--which those growing up in the 60s and 70s will remember well. Heating the lower portion causes colorful blobs to rise and then fall. Here is a video of one for the younger crowd:

People frequently ingested illicit substances while watching such displays, but meteorologists have no need for such aids--the convection is more than enough.

On these cool spring days you can watch the atmosphere go unstable--either by keeping your eyes on the clouds or by viewing one of the many cam videos--
My department has a good one:

By the way, spring is typically the most unstable time of the year around here. The atmosphere takes time to warm up and spring often brings some of the coldest temperatures aloft, while the strengthening sun causes the surface to warm up more quickly.

So put on a warm sweater and enjoy the convection...it is a great show, with some of the cauliflower-shaped cumulonimbus rising several miles into the sky.

Finally, let me note that the big local meteorological gathering of the year will occur on May 13-14th...the NORTHWEST WEATHER WORKSHOP. Meteorologists from throughout the Northwest gather to talk about the latest in our regional weather and layfolk (like most of you) are very welcome. Topics will include everything from radioactivity from Japan and the latest on the new radar and local modeling, to a panel discussion of the use of social media to communicate weather information.

The web site for the meeting, which included the agenda, is found at


You can register for the meeting and/or the Friday-night banquet if you are interested.


  1. Although I know the concept of "lapse rate" I do not know what "lapse" means or more specifically what its derivation is.

  2. I want a sunny and 70 degree day so badly!!! The clouds were definitely fun to watch today, though.

  3. Thanks! It has been cold, but your perspective cheered me up.

  4. The first swallows arrived at my house this morning. I'm going to be very upset if they die in a late freeze :(

  5. Cliff, it might be of interest to your readers to learn about the Pacific Decadal Oscillation (PDO)if you haven't already covered this topic. PDO is another long term climate cycle that also may be playing a role in our unusually cool spring.

  6. Got my 1st sunburn of the year (on a sailboat) yesterday. Cool temp fooled me. Thanks for including the explanation of the sun as strong as in August.

  7. I've hardly even noticed the longer days. It's been so cold, damp, and depressing that I haven't even been outside much in the evenings.
    I have a backyard observatory that hasn't been open to the night sky since February 1st. I have the wrong hobby for this area. It used to get a lot more use, but the last few years it's been getting worse.

  8. Snow is mixed in with rain here over in Kingston. 39F. Doesn't feel like April.

  9. Since it’s hailing outside today, I found this on the komo4.com website that sums it up best…

    ███████████████░░░░░░░░░░░░░░░░░ 44% DONE
    Install delayed. Please wait.
    Installation failed. Please try again.
    404 error: Season not found. Season "Spring" cannot be located. The season you are looking for might have been removed, had its name changed, or is temporarily unavailable. Please try again.

  10. This was hilarious. Oh, and informative.

  11. If you want to see lapse rate in action go to tiger mountain on a partly sunny spring and see paragliders 6000ft in the air!

  12. There is a "Cult of the Lapse Rate", otherwise known as glider pilots, who call in sick on sufficiently unstable days. We seek rising thermals the way that surfers seek waves. When you catch a good one, it's a heck of a ride. This one at Tiger Mt last week took me up nearly 2,000' in two minutes:


  13. There is a local "Cult of the Lapse Rate" otherwise known as glider pilots, who call in sick on sufficiently unstable days. We seek thermals the way surfers seek waves-- when you catch a good one it's a heck of a ride. Like this one on April 8 that took me up 2,000' in two minutes.


  14. Wild evening here in north Tacoma, near UPS. Around 830pm (Monday 4/18) In the space of ten minutes we had: heavy rain, graupel, graupel and snow, all snow (for several seconds), then lighter rain (for a few minutes). A couple miles away..nothing. If you were not watching, you would have missed the whole thing.

  15. 34F on my drive into PSNS today. Very cold. Great spot on KOMO1000 News Cliff. Good stuff. Keep up the bloggin.

  16. Tony (and all sun lovers), Remember the sun's UV strength has nothing to do with temperature. It basiclly depends upon three things, even given a clear day. It depends most importantly on the sun's altitude (height above the horizon), it depends on the observer's altitude above sea level, and it depends on the ozone density in the upper atmosphere. This is usually lower in the tropics, other things equal, but it doesn't vary much at a given location. A good general rule is, if your shadow is shorter that you are the sun's UV intensity is a force to be reckoned with. Or you can check the UV index.

  17. Cliff, you inspired me to set up a webcam and look at the unstable air... and wow, it really worked!


    Even a mini-anvil shape to a cloud and I believe a cold downburst that instantly puts a line of dark clouds in view??/

  18. Another time lapse on the 18th ...same day over Kirkland ...the view from 'Viewridge'



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