To weaken Gorge, Bay Area Peninsula & coast winds.
The Columbia River Gorge and the San Francisco Bay Area Peninsula and coast have had unusually weak winds the last 2 weak. Sometimes this was due to monsoonal clouds aloft and even sprinkles. Sometimes is was related to weak pressure gradient in the area. Let’s explore some of the major causes of this wind drought. In a recent blog on monsoonal clouds I explained how these clouds weaken the wind. But normally monsoonal clouds are a 1-2 day event. Yet here we are a week later and there is still mention of these clouds in the forecasts! Meteorologist call this a stagnate pattern. But before we explore that stagnation let’s look at another issue
Meanwhile the North Pacific High, that giant clockwise spinning feature located between the west coast and Hawaii has been greatly distorted in recent weeks and has kept that distortion much of that time.
Today, July 29 the images to the right show the typical distortion of the North Pacific High.
Looking at the top image find Portland and The Dalles which roughly bracket the western Gorge. Note how the isobars of the North Pacific High are closest together out in the Pacific. In a normal summer pattern those isobars would be concentrated over the Gorge making for a strong pressure gradient. So while the Columbia Basin has been hot and has low pressure the pressure gradient is not concentrated over the Gorge. Hence modest winds.
Now look at the 2nd image. Find San Francisco and note the Peninsula to the south and just north of Santa Cruz are the fabled wave sailing sites like Waddell. Note how the North Pacific High isobars are concentrated off of Cape Mendocino well north of the Bay Area. This positioning means the ocean wind west of the Bay Area is NNW rather than the normal NW.
NNW rather than NW sounds like a subtle difference but give the orientation of the California coast it means only a bit of wind reaches the Bay Area coast. Moreover NNW winds favor the creation of a small eddy west of the Golden Gate that further weakens the coast and Waddell winds.
Will finish this later today.