COOLING ARRIVES LATE FRIDAY. (VERY) SLIGHT CHANCE HIGH BASED SHOWERS SATURDAY OR SUNDAY.

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The giant high amplitude dome of high pressure that has brought record temperatures to Northern California for 10 plus days finally moves east Friday, and by Sunday temperatures across the North Bay will return to near normal.

Here is the position of the dome today, Friday, and then on Sunday, when the high pressure center is expected to be over the Four Corners region.

As you can see, when the high pressure dome shifts east, this will allow a mid level low pressure center to slide north along the California coast. The impact of that will be to increase our cooling onshore flow (good), and to usher in moisture from the south (not so good). The water in the atmospheric column is forecast to be near record levels for this time of year on Saturday into Sunday. That’s a lot!

Mostly we can expect it to be rather muggy for a couple of days (sat, sun), but you can see the predicted northward flow of subtropical air.

Anytime this kind of thing happens (subtropical moisture inflow) dry lightning is a possibility for our region, but any thunderstorm activity in our area is very unlikely this time. The atmospheric dynamics just don’t support it on any large scale. In fact, the NWS puts the chances of thundershowers at just 5-10 percent for the Bay Area region. But showers will be likely in the Sierra, especially Saturday and Sunday.

If this changes we’ll bring you an updated post. Stay tuned!