What Is A Thermal Trough?

Story Published: Mar 13, 2008 at 1:13 PM PDT

Story Updated: Mar 13, 2008 at 1:13 PM PDT

By Steve Pool

SEATTLE - Also known as a "heat low", it's caused by an area of intense heat. Since hot air rises, it'll leave an area near the ground where there is less air around, causing lower pressure at the surface. Air then rushes in from nearby areas to replace the hot, rising air.

When the trough is positioned to our west, that will pull hot surface air from Eastern Washington, down the western slopes of the Cascades, and out toward the offshore trough. As a double whammy, as air sinks, it also warm, making it feel even hotter.

We'll stay hot until the trough moves overhead and then jumps the Cascades into Eastern Washington. At that point, now we're on the west side of the trough, where air is rushing in from the cool, Pacific ocean and it'll cool us off quite rapidly.

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