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As low pressure passes through the Pacific Northwest and into the Northern Rockies early this week, a brief fall-like pattern of northerly offshore winds is expected to develop across the North Bay mountains late Tuesday and early Wednesday.

The National Weather Service in the Bay Area has issued a Fire Weather Watch effective Tuesday at 11PM through Wednesday morning at 11AM for the mountains of the North Bay and East Bay.

On Tuesday and Wednesday a low pressure system is forecast to be moving east through Washington state.

By late Tuesday night, winds are predicted to increase in the northern Sacramento Valley. The strongest winds, 30-50 MPH, are expected to stay at 2500 feet and above, but these may extend into the mountains of the North Bay by early Wednesday morning. This is how two models see winds at 2500 feet, at 5AM on Wednesday morning.

At this point it appears that the strongest winds will not mix to the surface. Here is the surface wind plot for 5AM Wednesday. This forecasts that strong surface winds may be isolated to the mountaintops of northern Napa and Sonoma Counties.

Of course, the northerly winds will also bring dry air into the region, lowering relative humidity values across Northern California, and increasing the danger from any fire starts, especially in the mountains.

At this point the period of strong winds is expected to be brief, and should end later in the day on Wednesday.

Due to northerly winds, smoke from Northern California fires may increase across the Bay Area and North Bay. This is how one smoke forecast shows conditions early Wednesday, as northerly winds push smoke south. Uncertain is how much of this smoke will reach the Bay Area and North Bay before wind directions change.


The National Interagency Fire Center has issued this general update for the Northern California region.

“Winds turn NW-N-NE Tue night & last thru Wed night with general pk gusts 25-35 mph & localized gusts to 40-50 mph favoring known Gaps-high Ridges Coastal Range & portions of Sac Vly & W. slopes of Cascade-Sierra Ranges as well as N. Bay Hills.

Heavy smoke will change directions due to this wind shift & affect portions of Sac Vly & Coastal Range/Bay Area that hasn’t been impacted as much past week”

We will keep you updated on this expected offshore wind event as conditions develop.

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