Two words: Delta. Breeze.
This weather feature is so significant it can take us from highs in the 100s one day to 70s the next.
So why don’t we always have it?
Let’s start here. The valley warms quicker than air over the ocean. This creates a big temperature difference. The warmer valley air is less dense and rises. The cooler marine air is denser and sinks.
In order for the atmosphere to even out that temperature difference, it will “pull” the cool air inland toward the warm air. This brings that huge relief in hot temperatures.
All this is happening in a transition area between the Bay Area and the valley called the delta, thus the name Delta Breeze. It’s lower than the surrounding area, so it’s like taking that cool air and shooting it through a tunnel until it reaches the valley and can spread out.
Alright, that’s here on the ground. The other big part of this is what’s happening way up there in the atmosphere that helps to get that cooler breeze to the valley. This is usually a low in the North Pacific. It has a counterclockwise spin that starts that flow from the Pacific to the valley.
If that low isn’t there, we’ll sit for days in the 100s.
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