Record-high temperatures for this time of year are possible in the Tri-Valley starting Saturday and lasting at least through Monday when the thermometer could hit 101 degrees.
The high temperatures follow a week of below-normal readings.
Clear skies are bringing a warming trend that could move temperatures as much as 30 degrees above normal, according to the National Weather Service.
Even coastal locations and downtown San Francisco could see highs in the 80s on Sunday and Monday. Weather officials said they can't rule out temperatures in the upper 80s to near 90 on Sunday afternoon in some spots along the coast.
In the Tri-Valley and other inland areas, temperatures in the high 90s are expected on Sunday and higher on Monday.
Gilroy will probably be the hottest spot in the region and could reach 105 degrees, meteorologist Steve Anderson said.
Anderson said the heat will really only a few days. Widespread cooling is expected by the middle of next week.
Editor's note: Keith Burbank, Bay City News, contributed to this report.