Winter fog in Willamette Valley, Oregon

Fog in Willamette Valley: Shades of dark green land viewed from space with a stretch of stark white running down the center.
Natural-color satellite view of dense fog in Willamette Valley, Oregon, on February 10, 2022. NASA satellites have so far seen 3 periods of extended fog there in 2022: January 14-17, January 22-29, and February 8-12. This week’s forecast is for sunny skies, though! Image via Landsat 9 satellite/ NASA Earth Observatory.

Fog in Willamette Valley

NASA Earth Observatory released this satellite image of Oregon’s Willamette Valley on Sunday (February 20, 2022). It shows a long, dense stretch of fog blanketing the valley: the result of a temperature inversion.

NASA satellites have viewed three extended periods of Willamette Valley fog this year. They happened on January 14-17, January 22-29, and February 8-12.

In a January 24, 2022, weather report, CBS-affiliated TV station KOIN-6, covering Oregon and southwest Washington, had a good explanation and visual about temperature inversions. Joseph Dames of KOIN said that during a temperature inversion:

… the surface will be cooler, with a warm layer above. That warm layer prevents pollutants from escaping. This also keeps the temperatures colder at the surface, allowing for fog to form … Cold air sinks to the valley floor during the winter months, as if we are in a cold bath.

Want the forecast for Willamette Valley this week? Click here

Graphic showing cold air above, warm air below, with arrow pointing upward.
Temperature inversions can cause dense fog over cities, too. And they can create hazardous driving conditions. Graphic via Joseph Dames/ KOIN-6.
Panel on left shows warmer air below cooler air; opposite on right.
In a temperature inversion, warm air is above a layer of cooler air. Image via University of Missouri/

Bottom line: Oregon has already seen at least three extended periods of valley fog this year as a result of temperature inversions. When this happens, temperatures are colder near the ground while the air above is warmed. The warm layer prevents pollutants from escaping, trapping fog and causing cold air to sink.

Via KOIN-6

February 22, 2022

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