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 slopes, 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 slopes, 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.
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