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As the week progresses, the North Bay will transition from cool onshore breezes to near record heat that will accompany high pressure moving in from the desert Southwest.

In preparation, the National Weather Service has issued a Heat Advisory for the North Bay and much of the Bay Area from 11AM Wednesday morning, to 11AM Thursday. Beginning Thursday, when heating reaches its peak, an Excessive Heat Warning will be in effect from 11AM through 1PM Friday for a large part of the North Bay.

A bit of good news. No offshore wind events are forecast, rather surface winds will be mainly from the west or northwest, but confined mostly to the coast.

Monday afternoon, a trough of low pressure was to our northwest, and strong high pressure to our southeast. (Images 1 and 2)

Beginning Tuesday the strong high pressure dome will push east, into California, as low pressure moves off to our north and east. The high is expected to reach its peak intensity over California on Thursday. (Image 3)

That will correspond with the highest temperatures. Across inland Northern California, all time records for the date may be set. (Image 4)

For the Bay Area and the North Bay, inland areas will be hot, reaching 95-108 degrees. But, a continuing onshore breeze is expected to keep the coast, and locations within a few miles of the coast, relatively cool. The NWS released this graphic showing the likelihood of cities in the Bay Area hitting 100 degrees this week. (Image 5)

Of course, temperatures often exceed NWS forecasts, especially in the micro climates of the North Bay. If you are in a warm area like Windsor, Healdsburg or Cloverdale, expect highs Thursday, and perhaps Friday, to be 100-108 degrees. Far inland areas like Lake Berryessa may reach 110.

The NWS has issued a relative heat risk map, which shows the influence of the onshore breezes in keeping areas near the coast cooler than well inland. (Image 6)

By Thursday, much of the West will be far hotter than normal. This GFS forecast shows that central Sonoma County may be 27 degrees above average at 2PM Thursday. That would be well over 100 degrees in many areas. (Image 7) (the Euro shows slightly cooler temperatures by about 5 degrees)

Whatever happens, it will be hot. Minor cooling looks to begin Friday with more robust cooling through the weekend as high pressure moves away from California. By Monday, temperatures may be back close to normal. (Image 8)

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