With expected temperatures around the 100-degree mark, the National Weather Service issued a Napa County heat advisory for Wednesday and Thursday.
The advisory covers much of the Bay Area and coastal valleys, with temperatures in the hottest interior locations potentially reaching 107 degrees.
The Weather Service said south Napa could hit 99 degrees on Wednesday and 98 degrees on Thursday. Calistoga could reach 102 degrees on Wednesday, then drop a degree on Thursday.
Hot temperatures will create a situation in which heat illnesses are possible. People should drink plenty of fluids and take extra precautions if they work or spend time outside.