Dangerous heat persists in your Tuesday forecast, and the threat of mountain thunderstorms will be possible across the northern Sierra today. The Excessive Heat Warning is now set to stay in effect in the valley and foothills through 8pm Tuesday night, through 9pm Tuesday night in Trinity County, through 10pm Wednesday night in Lassen and Plumas Counties, and through 11pm Thursday night in Modoc and Siskiyou Counties. High pressure centered to our northeast will continue to leave us very hot and dry today, but low pressure off the coast will provide a modest Delta Breeze and bring the potential for mountain thunderstorms to our region over the next few days. Conditions are mostly clear overhead this morning, and we'll be sunny through your Tuesday. Only some limited clouds will move into the eastern slopes of the Sierra this afternoon, and the threat of thunderstorms is expected to stay to our south along the California and Nevada border. Temperatures are starting out in the 60's to 70's in the valley and foothills this morning, while our higher elevations are starting out in the 50's to 60's. South winds to 10mph are expected today, and gusts up to around 20mph will be possible this afternoon and evening. Humidity will dip into the 9 to 21 percent range this afternoon, so it will be very dry across our region. High temperatures are projected to end up in the 102 to 109 degree range in the valley, 90's in the foothills, and 90's to lower triple digits in our higher elevations this afternoon. The dry and hot conditions will result in moderate to high fire danger today. Fuels are very dry and primed to ignite. It's very important to stay cautious as to not start any new fires, especially since we have several actively burning across our region already.
High pressure will continue to be centered off to our northeast over the next few days, and that will keep our high tempratures well above average. The low pressure off the coast will provide some modest cooling to our region through the remainder of this week, but it will really only be keeping our high temperatures in check. This will also draw in enough moisture to bring instability into our forecast in the northern Sierra. The threat of thunderstorms will become somewhat more widespread along the eastern slopes of the Sierra on Wednesday and Thursday. High temperatures in the valley will end up in the 90's to lower triple digits late this week through the weekend, while mountain and foothill areas continue to top out in the 80's to 90's through your 4th of July Weekend. There will be a chance for some thunderstorm activity moving as far west as the eastern Shasta County mountains on Saturday, but that threat does not currently look as likely on Sunday for the 4th of July. Hot and dry conditions will continue to dominate our region through your entire extended forecast. Dry and hot conditions are also expected to persist through next week.