A swath of the North Bay and much of the Sacramento Valley are under a Red Flag Warning starting Tuesday night and lasting through Wednesday evening, as the first bout of threatening fire winds arrives this season.

It wouldn't be late summer without a Red Flag Warning, and while we've been spared any significant fire threats so far this summer, that all ends tonight. The National Weather Service has issued a Red Flag Warning for a large area north of Sacramento and including the city itself, as well as parts of Solano and Napa counties, where PG&E power shutoffs could occur in the next 24 hours.

The Red Flag Warning begins at 11 p.m. Tuesday and runs through 8 p.m. Wednesday.

PG&E issued its warning of a potential public-safety power shutoff (PSPS) for seven counties on Monday, putting them under a fire weather watch — and this included parts of Napa, Lake, Colusa, Glenn, Shasta, Tehama and Yolo counties. As the Napa Valley Register reports, the largest of those potential shutoffs are way to the north, in Shasta and Tehama counties, where around 7,000 customers could lose power.

Fifty or fewer customers are expected to be impacted in the northern and eastern reaches of Napa County. Shutoffs could begin by 3 a.m. Wednesday.

Wednesday is expected to be the hottest day of the week, and that will be combined with 15- to 25-mph winds in the western portion of the Sacramento Valley, coupled with gusts from 30 to 35 mph, as the weather service predicts.

The National Interagency Fire Center further predicts gusty winds of 25 to 35 mph, with localized peak gusts as high as 45 mph, and this includes the Mount Diablo area as well to the Sacramento River Delta.

Coming behind this weather is a cold front that will significantly cool things down, here as well as up in Tahoe, for the Labor Day Weekend. That is expected to bring some possible showers as well in some spots.