January 14, 2009

Lowering Inversion and Low Clouds

As you can see from the satellite image this morning, some areas are in low clouds and fog, while the southeastern sound, the mountains, and the coast were in sun. The lowlands of eastern Washington were also cool and cloudy.



The inversion aloft has been progressively lowering in altitude. The picture below is extraordinary in showing this. What you are seeing are temps and winds above Seattle ( red temp, blue wind) over the past day. The zone of big changes in temperature (lots of red lines close together) is the inversion. Note how it has progressively lowered...right now the base of the inversion is around 600 m. The plots of temperature at particular times (second plot below), shows the inversion changes even more graphically. Within rougly 300 m (1000 ft), the temperature increases nearly 20F (10C)! I bet the top of Tiger Mountain (2500ft) is in sun now (let me know if anyone has been up there this afternoon).

Above the inversion it is really warm and toasty. The observations at Paradise (around 5500ft) showed temps in the mid-50s. This will be true for a number of mountain locations (e.g, Mt. Baker, Crystal). So this is a good time for a mid-elevation hike or ski trip in the mountains.

Air quality has held out...mainly because the inversion has been quite high, allowing the mixing of pollutants in a substantial volume of air (see graphic from Puget Sound Clean Air Agency). With lots of clouds we have not formed a surface-based inversion, and such inversions are associated with the worst air quality situations. However, as the overlying inversion descends, air quality may well decline.

The current long-range forecasts, out 4-5 days, are emphatic that high pressures and resulting inversions will hold out through the period.


16 comments:

  1. It hit 64 F at Paradise today at 2:00. Cliff sure called it right!

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  2. Cliff: what's the best way to look for forecasts of inversion height in the output from the various mesoscale models?

    Only in the soundings. Or is there a another way?

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  3. But I'll bet you couldn't see too much from the top of tiger mountain with it being so hazy...
    Or does the visibility improve once above the inversion?

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  4. 64 at Paradise? I bet it was dreamy up there! Though I did just finish reading an informative article on the storms of '06 and their impact on Rainier in Backpacker Mag. So maybe I shouldn't get so thrilled at the nice weather. Because you really need to keep your glacial pack up there.

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  5. I live on Tiger Mt, about 800 feet, and we've been in glorious sun all day, although barely above 40 degrees this afternoon. I hiked some trails near our house, up over 1000 feet, and it was cold but beautifully clear. There were a few small mud slides from the heavy rains, and one very large chunk of a power line access road, about 75 feet, has washed out--simply slid right down the mountain, taking out trees and everything else in its path. Pretty impressive!

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  6. Kevin...the soundings and the time-height cross sections have that information...cliff

    1000 ft is not high enough to warm up...got to go to the top!

    PS: the inversion base is now 420 m and most of the warming occurs by 900m (roughly 3000ft). Remember cold air moves through the passes...so they won't be warm at that elevation.

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  7. Out here at my house on Ring Hill, in East Woodinville, the high for today was 38 F, and that was very briefly during the afternoon. It was overcast most of the day.

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  8. We now have an _Air Stagnation Advisory_ http://www.wrh.noaa.gov/sew/
    in effect as of 10PM tonight lasting into Saturday. As a relative newcomer to the area (arrived here 18 months ago), I never heard of such a thing. Do they happen often??? And last so long???

    As always, thank you so much, Cliff, for what I am learning here.

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  9. Cliff--

    An example of this inversion is evident at Stevens Pass. According to their website, this afternoon it was 34 at the base (approx 4000 feet) and 44 at the top (approx 5800 feet). A few years ago I was headed for Stevens Pass and checked the website before leaving and it said 12 degrees at the base and 35 at the top. I thought it was a typo--turns out I was wrong. When approaching the summit (the last 1000 feet or so) the temp plummetted from 30 or so to 12 at the top. Amazingly, once reaching ski area it was RAINING at the road level. Everything was coated with ice as the rain froze on everything it landed on. A very thin layer of very cold air with much warmer air aloft. I had a few beers and went home, not good skiing conditions.

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  10. Cliff--

    An example of this inversion is evident at Stevens Pass. According to their website, this afternoon it was 34 at the base (approx 4000 feet) and 44 at the top (approx 5800 feet). A few years ago I was headed for Stevens Pass and checked the website before leaving and it said 12 degrees at the base and 35 at the top. I thought it was a typo--turns out I was wrong. When approaching the summit (the last 1000 feet or so) the temp plummetted from 30 or so to 12 at the top. Amazingly, once reaching ski area it was RAINING at the road level. Everything was coated with ice as the rain froze on everything it landed on. A very thin layer of very cold air with much warmer air aloft. I had a few beers and went home, not good skiing conditions.

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  11. Really glad I don't live at Paradise! 64 in mid-January? That's just plain UGLY!

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  12. Skiing near snoqualmie today at around 5000' my thermometer read 55 F.

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  13. I can vouch for Cliff's experience on Tiger Mt. I did not go up today, but I've been regularly running the trail to Poo Poo Point and beyond for nearly seven years. Many times I've started with below freezing temps and frost at the bottom and found spring-like temps at the top. Sometimes the transition takes place within just a few feet of elevation. It can be very dramatic--and delightful. The only problem is over-dressing!

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  14. More than one person today has remarked to me that they heard on the news that it is supposed to be sunny on Friday and Saturday. However, most live near the Puget Sound, so I tell them to take it with a grain of salt. They look at me funny because I'm not _____ on KIXX, so obviously what do I know?...They say on the TV that it will hit the high 50s Friday. I tell them if it is sunny, enjoy it...

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  15. JayDee: the sounding forecasts form MM5-NAM look like the possibility of breaks in the fog on the afternoons of Thursday, Friday and Saturday.

    See the wet bulb and dry bulb temps actually diverge each afternoon ...

    http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_e_snd_ksew+///3

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  16. Hmmm, I just looked at MM5-GFS sounding and it seems more enthusiastic about no fog over the next few days.

    http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_x_snd_ksea+///3

    WRF-GFS is a little more pessismitic but looks pretty good too.

    http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_snd_ksea+///3
    I guess it depends upon which model you beleieve!

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