Temperatures will warm to 15-20 degrees above normal across interior Northwest California Thursday through the weekend with highest exceeding 100 degrees for many valley locations. The heat will begin in the south in Mendocino and Lake counties where a Heat Advisory has been issued for Thursday and Friday when the HeatRisk will be in the Moderate to Major category. Heat will then spread north into Humboldt, Trinity, and Del Norte Friday into the weekend though overnight lows may be a bit cooler, lowering the HeatRisk overall. To combat the heat, wear light fitting clothing, stay inside during the hottest times of the day, and drink plenty of fluids. And remember, never leave kids or pets inside an unattended vehicle. Vehicles heat up quickly and can become deadly within minutes.