Be prepared for very active conditions and high fire danger across northern California today. Low pressure is still parked off the coast of central California, and will work to keep our high temperatures in check and bring unstable conditions into our forecast this afternoon and evening. The threat of thundertorms will become more potent and widespread today, and is resulting in a Red Flag Warning for high fire danger being issued for portions of the valley, the foothills, and some mountain areas. The Red Flag Warning will go into effect at noon and last through 9pm tonight in Tehama County, Shasta County, the Butte County Foothills, and a portion of Plumas County. The Red Flag Warning will also go into effect at noon in Trinity, Siskiyou, and Modoc Counties, but will expire at 8pm in Trinity County and 7pm in Siskiyou and Modoc Counties. Our fire danger is being driven by the threat of thunderstorms that could include dry lightning, and localized gusty winds over dry fuels. We're starting out with mild conditions this morning and mostly clear conditions overhead. Temperatures in the valley are mostly in the 60's for the start of your Thursday, while foothill areas are in the 50's to 60's, and mountain areas are in the 40's to 50's. We'll have wind out of the south to 10mph, and humidity will dip into the 17 to 30 percent range this afternoon. High temperatures will end up in the mid to high 90's in the valley, upper 70's to upper 80's in the foothills and Sierra, and upper 80's to mid 90's in the Northern Mountains this afternoon. The threat of thunderstorms will start to ramp up this afternoon and will persist into tonight.
The low pressure area of the coast of central California will start to break down and track east through southern California on Friday, and high pressure will begin to build into the Pacific Northwest. This will result in the threat of thunderstorms becoming limited to the northern Sierra, and our high temperatures heating up by a few degrees on Friday afternoon. Sunny to mostly sunny conditions are expected across most of our region on Friday. Low temperatures will be similar to Thursday morning on Friday, but high temperatures will end up 5 to 6 degrees warmer in most areas. Valley locations will top out in the upper 90's to triple digits on Friday afternoon, while foothill and mountain areas top out in the 80's to 90's.
High pressure centered to our north will dominate the forecast across the entire West Coast from this weekend through early next week, and will drive dangerous heat across northern California during that time. An Excessive Heat Watch has now been issued for the valley and foothills from Saturday through Wednesday, and an Excessive Heat Watch is also set to go into effect from Saturday morning through Monday night in Trinity County. An Excessive Heat Watch is also set to go into effect from Sunday through Wednesday along the eastern slopes of the Sierra. An Excessive Heat Warning has been issued for Modoc and Siskiyou County areas from 11am Saturday through 11pm Tuesday night. Valley areas are projected to end up in the 105 to 112 degree range this weekend, while foothill and mountain areas top out in the 90's to lower triple digits. Very hot and dry conditions are projected to continue through all of next week. Valley areas will have overnight low temperatures ranging from the upper 60's to lower 80's, and high temperatures in the triple digits all week next week. Mountain and foothill areas can expect temperatures to range from the 90's to triple digits through most of next week as well. Make sure you're keeping up with our coverage as the threat of fire danger ramps up today, and plan ahead to beat the dangerous heat on the way in your extended forecast.