The visible satellite image this morning was an October classic:
Low clouds (stratus and fog) within the valleys of western Washington, Oregon, and southern British Columbia.
The Seattle PanoCam said it all (below) and contrasted sharply with the cam on Crystal Mountain (also shown).
To show this, the temperature above SeaTac airport, based on aircraft data, is shown below.
52 F at the surface and 65F at 3000 ft!
Autumn is the time of the year when everything comes together to produce fog and low clouds, as shown in the figure below.
Why such an inversion (temperature increasing with height)?
With clear skies above, the surface can radiate (infrared) heat to space, allowing surface cooling.
Nights are getting much longer, providing more time to cool.
And there is a ridge of high pressure aloft (see upper-level map above), which not only produces clear skies and good radiative cooling at the surface, but also forces sinking aloft, which results in upper-level warming (air warms by compression when it sinks).
Orange colors indicate higher-than-normal 500 hPa heights (higher pressure than normal, around 18,000 ft). This is called ridging and is associated with sinking and warming air aloft.
Autumn is the time of the year when everything comes together to produce fog and low clouds, as shown in the figure below.
October is the foggiest month of the year.
If you enjoy hiking and want a meteorological treat, try an early morning hike in the foothills of our local mountains. You will start cold, but rapidly warm up as you ascend through the inversion.
Just pick a day with a ridge overhead, like today.
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Potential for Aurora tonight.
The Planetary K Index is elevated, and some folks (such as Greg Johnson of Skunk Bay Weather) saw a good display last night.
No guarantees, but there could be a repeat tonight.
Old Seattle guy here. Fog used to be standard in the last half of August. Now not so much. Also - do you remember Christmas of 1985? 6? when SeaTac was fogged in for ~TWO WEEKS. I had to drive from LA in the tule fog.
ReplyDeleteWe live about 1-1/4 miles north of Snoqualmie Falls, about 550-ft MSL. We had fog in mid-August and several times since.
DeleteI'm too young to remember Sea-Tac being fogged in for two weeks in 1985/1986. But I do know that fog in August is a regular occurance on the Grays Harbor coast. August is sometimes referred to August as "Fogust" out there.
DeleteI remember that year well as I was in my 20's and working at my first job and recall when the fog would never totally go away and remained all day for quite a while and if memory serves, it was during the week between Christmas and New Years and recall the pollution settling on the cars at the time and recall it remaining hazy in the distance when the fog lessened as the day progressed but again, never totally went away.
DeleteI just recall it was gloomy, hazy and very still.
I'll try and look for an aurora tonight... But so far, every time I have seen one I did not know it was coming, and every time I expected one, it wasn't there!
ReplyDeleteAs for the inversion I went rock climbing in Mazama yesterday, my car thermometer said 82 degrees around 3 P.M. and is was about 56 degrees on Washington Pass when I drove home.
ReplyDeleteDefinitely foggy last week in the mornings while commuting to Kent. On Thursday, it was pea soup in Tacoma, virtually to street level but as I got onto SR 16 to merge onto NB I-5, the fog lifted some and rose about 200Ft up so the highway was clear, but not so much above me for most of the way to SR 516/Kent Demoines Rd so I can drive to SR 181 to go north for the final length to work.
ReplyDeleteIt was quite foggy in Kent on 516, but it did lessen up somewhat as I turned left onto SR 181/68th Ave S. to head north for the final stretch.