Looking at this animation first notice the upper trough and upper ridge that are moving towards the Golden State from the west.
Focus on the upper ridge which is a northward extending loop of upper-level winds at the 500 mb. level which is 18,000 feet above the surface.
This upper ridge brings very warm air from equatorial areas further northward. The light blue color in the next image shows this warm air aloft. The warm air in the area of the upper ridge is descending air that compresses as it nears the surface making for even warmer air.
The next image shows how the upper ridge and compressional heating warm up the surface air. Over the ocean this surface heating is muted by the constantly moving waters. But take a look at the red color over California and the southern Great Basin. That reflects that the heating induced by the upper ridge keeps heating the landmass day after day hence the heatwave.
Now for the complex part.
Focus on the white isobar lines that show zones of equal pressure.
Notice the isobars moving into the Pacific Northwest and far Northern California. This high pressure causes NNW winds aloft over much of California. This brings more warm are into the state from Nevada and the Great Basin.
Now check out the zone of isobars extending from Central Valley and Southern California Deserts way over the coast.
In the San Francisco Bay Area having low pressure over the coast weakens the pressure gradient so the Bay sees weak coast wind.
In Southern California having low pressure over the Southern California Bight helps to product a large eddy in the Southern California Bight and also weakens the coast winds.
So when will the heat subside and more seasonal winds return? Here is a hint. Keep an eye on that pacific upper trough!
diff ridge into Oregon and far Northern California. This causes: 1. NNE winds just aloft with Mt. Diablo 34g39 predawn. 2. Northerly Sherman Island winds.3. The ocean winds have a bit of NNW. 4. The Central Valley thermal low expands over the coast.