From a news release:

Extreme heat impacts are expected to continue through at least Thursday as the longest stretch of hot weather of the season is forecast, the National Weather Service reports. High temperatures will be around 10 to 20 degrees above normal most days.

Sunday may be a few degrees cooler than the rest of the week, though it will still be very hot. There will be little to no overnight relief. With this long duration extreme heat event, significant heat impacts are expected for the general public, especially for those sensitive to the heat, pets, and livestock.

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There is a chance of isolated thunderstorms with little to no rainfall over much of NorCal today through tomorrow. These dry thunderstorms could produce fire starts, so a Red Flag Warning has been issued. Isolated afternoon mountain thunderstorms are also possible over the Sierra Crest through Tuesday.

KEY POINTS

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Impacts

• The entire population could be impacted by long duration extreme heat with little to no relief overnight
• Heat related illness to humans, pets, and livestock likely with extended outdoor exposure
• Isolated thunderstorms across the Valley, foothills, and mountains could start new fires

Forecast Confidence

• High for long duration extreme heat event through next week
• High for fire weather concerns due to thunderstorms with little to no rainfall across the Valley, foothills, and mountains today (updated)
• Medium for isolated afternoon Sierra thunderstorms through early next week

Timing

• Sunday – Thursday
• Long duration extreme heat event today through Thursday with moderate to extreme heat risk impacts
• High temperatures: Valley 102-112°, foothills 93-107°
• Little to no overnight relief with minimum temperatures in the Valley and foothills in the 70s to low 80s
• Fire weather concerns due to possibility of thunderstorms with little to no rainfall over the entire Valley, foothills, and Sierra today through tomorrow morning (timing updated; see Thunderstorms.png)
• Isolated afternoon thunderstorms possible over the Sierra Crest through Tuesday