|Visible light image of Washington state from GOES West weather satellite, 2:00 pm Seattle time Thursday Dec 23, 1999.|
All of the smooth, light colored areas are low clouds and fog - very
pronounced over the eastern half of the state; less so on the west side.
The brighter white, more sharply defined areas are snow covered mountains
that rise above the low lying fog. The Seattle area was actually
mostly clear today, as can be seen by the dark hole in the fog, with Lake
Washington being the even darker squiggle in the center of the clear area.
The fog and low clouds are a result of the high pressure weather system
that has been parked over the eastern Pacific and western US the last few
days. This time of year, such a pattern quickly results in an atmospheric
temperature inversion, where cold air is trapped right near the surface,
while much warmer air lies a couple thousand feet up. While Seattle
and the lowlands struggled to get out of the 30s today, Paradise on Mt.
Rainier climbed to 56°. and Hurricane Ridge in the Olympic mountains
reached a relatively scorching 60°F!
|GOES West composite visible - infrared image of western US and northeastern Pacific, 2:00 pm Seattle time Thursday Dec 23, 1999|
Composite of infrared (colored blue) and visible (colored orange) images.
The effect of this is to show relative warmth and altitude of clouds.
The orange colored clouds are low and relatively warm, so they don't show
up as well on the infrared image (where brightest = coldest). The
white-blue clouds over the ocean mark weak weather disturbances where there
are clouds higher in the atmosphere, the more widespread low clouds and
fog common over the Pacific this time of year show as orange. The
fog over Washington state shows as mostly orange, hence low and relatively
warm. The snow cover in the mountains also shows as orange, since
this snow is not much colder than freezing, 32° F. The higher
clouds, and the whole atmosphere over northern Canada (upper right corner
of image) are much colder - on the order of 10°~30° below zero