Sweltering heat was blamed Sunday for at least three deaths in Northern California, including a resident at a nursing home who died after the facility's air conditioning system failed.

Triple-digit temperatures covered much of the Southwest. In California, the power grid manager warned the state might declare an emergency for the second-straight day due to soaring electricity use.

Excessive heat warnings were in effect through parts of Southern California, where temperatures were expected to reach 99 degrees in downtown Los Angeles and 115 degrees in nearby Woodland Hills, where the mercury hit a record-setting 119 degrees Saturday. National Weather Service broke heat records Saturday. On Sunday, forecasters issued a heat advisory for the southern and eastern regions of the Bay Area.

State electricity officials warned of possible power emergencies if demand remained high and a power plant that went off-line Saturday isn't fixed.

"Today's going to be close," said Gregg Fishman, spokesman for the California Independent System Operator.

Scorching temperatures were the result of a high-pressure system mixed with humidity from subtropical moisture streaming in from the Gulf of Mexico, according to Jamie Meyer, a National Weather Service meteorologist.

The high pressure will drop off somewhat in the coming days as will the humidity, causing temperatures to fall a few degrees each day until midweek, she said.

Heat waves left much of the country sweltering last week, with temperatures soaring into the upper 90s and higher from coast to coast and heat related deaths reported in Oklahoma, Illinois, Kansas, Missouri, Pennsylvania, Arkansas, Indiana, South Dakota and Tennessee.