Just as a boa constrictor envelops and tightens on its prey, so is the high pressure over us tightening and strengthening the inversion over our heads!
Each day the inversion layer over the Puget Sound lowlands has lowered and gained more better definition, and with it the tops of the low cloud layer have descended. We are being squeezed....meteorologically, of course.
The latest pilot reports report the top of the clouds are around 1200 ft, allowing some of the higher eastside hills to be uncovered.
The inversion is really extraordinary, with temperatures in the forties near sea level, while sixties are a few thousand feet above...even at night! During the day some low mountain locations jumped into the upper 70s to near 80F, while some Puget Sound folks were 30+ degrees cooler. Amazing.
To illustrate, look at the max temperatures Monday in the region. The dark green shows locations with HIGHS in the forties. Only a few miles away and perhaps 2-3 thousand feet up, observation sites reported mid-70s and higher. With bright sun.
in a previous blog. Anyway, this figure is a bit technical, but it shows a plot of temperature (right lines) and dew points (left lines) from some aircraft coming into Seattle-Tacoma Airport on Monday evening. HUGE inversion, with temperature increasing with height by about 20F in 2500 ft. (the numbers of the left give the pressure level 850 hPa is about 5000 ft).
There is very dry air above a very shallow saturated layer (where the temperature and dew point are on top of each other).
Why is this like a boa constrictor? The persistent high is strengthening the inversion in two ways. First, there is sinking motion with the high--stronger above and weakening near the surface. Sinking causes compressional warming and thus the warming is greater aloft than near the surface....this helps the inversion strengthen and lower. And high pressure and associated sinking stops clouds from forming aloft, which allows good infrared radiational cooling from the surface and the cloud tops. So we got a heater aloft and a cooler near the surface. What does that spell?
The inversion is getting so shallow, that we may have a chance to burn through it on Tuesday. The extent of the cloud coverage definitely was a bit less on Monday than on Sunday.
To show you how low the inversion is gotten, here is a wonderful picture this (Tuesday) morning from Peter Benda from his house in Bellevue at 1170 ft...the top of the cloud deck must be around 1000 ft:
Amtrak has the potential to tap the huge demand for sun and warmth. Just run regular "SunTrains" from Seattle across Steven Pass to Leavenworth or Wenatchee. Sun tan lotion included. The train could make a stop at the elevation at warmest temperatures. They would make millions.