Get ready for another day of hot temperatures and the potential for thunderstorms across northern California in your Friday forecast. High pressure off to our east will continue to keep us hot and will draw monsoonal moisture from the south into our region. That influx of moisture is projected to create enough instability to kick off more thunderstorm activity in our mountain areas today, and we'll have a slight chance for some thunderstorm development in the northern end of the valley this afternoon and evening. The threat of thunderstorms brings elevated fire danger concerns to our forecast, as any thunderstorm activity could be accompanied by dry lightning and locally eratic winds. A Red Flag Warning will be in effect from noon through 8pm Friday in Trinity County, and from 2pm through 11pm Friday in Modoc and Siskiyou Counties. The main driving factor prompting the Red Flag Warnings for high fire danger is the potential for thunderstorms. An Excessive Heat Warning is set to stay in effect in western Siskiyou County through 11pm Friday, and a Heat Advisory is set to be in effect in Trinity County from 10am through 8pm Friday. Thin clouds are tracking into northern California from the south to start the day, and we've continued to track showers across portions of the Sierra and southern Cascades overnight. Showers and thunderstorms will mostly be possible in our higher elevations this afternoon and evening, while the far northern end of the valley will have potential for some active weather late in the day. Clouds are expected to increase through the day. We'll start out mostly sunny in the valley and foothills but will become partly cloudy this afternoon. Mountain areas will become mostly cloudy by later this afternoon. Temperatures are starting out in the 70's to lower 80's in the valley, 70's in the foothills, and 50's to 60's in our higher elevations this morning. Winds are out of the north or northeast early today, but will again shift to become out of the south or southwest this afternoon. Humidity will likely dip into the 13 to 22 percent range this afternoon. High temperatures are projected to top out in the 103 to 109 degree range in the valley, upper 80's to upper 90's in the foothills, mid 80's to mid 90's in the Sierra, and upper 90's to lower triple digits in the Northern Mountains Friday afternoon.
Conditions will be very similar as we head into this weekend, but temperatures will trend down by several degrees on Saturday. Valley areas will range from the upper 90's to lower triple digits through this weekend, while foothill and mountain areas top out in the 80's to mid 90's. The threat of thunderstorms will continue in our higher elevations through Sunday, and we'll even have a slight chance for limited active weather down into the valley on Saturday. Overnight low temperatures will also stay very warm as clouds continue to track overhead through the weekend.
Low pressure approaching the West Coast will nudge the high pressure off to our east further to the east from Sunday into Monday. This will cut off the source of monsoonal moisture that's bringing the potential for thunderstorms to our area through the weekend. Temperatures will end up around average or a little below average early next week, and we'll have sunny skies. Stronger south winds will also be possible across our region as the low pressure approaches the West Coast. We're projecting dry weather, sunny skies, and around average temperatures through all of next week.