One of the sure signs that a heat wave is building into Western Washington and Oregon is to just take a peek at the temperature for Brookings on the southern Oregon Coast. ('BOK' is their NOAA Weather code)
Temperatures hit an amazing 101 degrees Monday after reaching 92 Sunday -- warmer than both Las Vegas and Phoenix that day (who were dealing with thunderstorms). Perhaps even more amazing is it only cooled to 80 degrees Sunday night -- a temperature that would break Seattle's all-time warmest night by 9 degrees. And again, Brookings is right on the coast!
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How can some place right next to a big pool of 50 degree ocean water get so hot? They can blame the mountains to their east. When a thermal trough builds up from California, it draws an east wind from the interior.
But as that wind sinks down the mountain range, it compresses and heats further, giving Brookings a number of days each summer when it could pass as a southern California coastal town. In fact, Brookings has a number of record highs at 100 or greater in the summer.
Forks on the Washington coast gets a bit of this effect sometimes too with winds sinking down the Olympics, but not as frequently as Brookings.
The effect in Brookings is pretty localized -- highs were in the 70s just up the coast a bit in North Bend -- but it is a bit of a "canary in the coal mine" that a thermal trough is indeed building, and could soon spell hot weather for the rest of the Pacific Northwest if that thermal trough moves north, as this current one is expected to do so.