The clouds are building over northern California as a storm system approaches from the Pacific Ocean. We can expect increasing clouds tonight with a chance of rain showers and thunderstorms through sunrise Friday. A trough of low pressure is already pushing clouds and moisture over our region today and a few light sprinkles of rain have fallen. The main body of active weather will not arrive until late tonight, with a line of showers and thunderstorms mainly between midnight and sunrise. Rain amounts will be fairly light, and lightning is possible. Lows tonight will range from the 40s in the mountains to the 60s in the valley. After morning showers we'll have sun Friday afternoon with cooler highs ranging from the 70s to near 90.
A Red Flag Warning covers most of northern California at this time, and it will expire piece by piece from west to east from Friday morning through Friday night as first the threat of lightning disappears, then the gusty residual wind quiets down by Friday night. We can expect the smoke to return to many parts of northern California in the wake of this fast-moving storm, but temperatures will start to rise. We don't have any other good chances or significant rain or strong wind through the rest of the 7-day forecast. Valley lows will begin fairly mild Friday morning, but will cool to the lower 60s beginning this weekend. Valley highs will begin below average Friday, but will rise above average by the first half of next week, staying in the 90s.