Residents here switching on their air conditioners to ward off an unusually hot night Thursday got a rude surprise: The power went off. That triggered a widespread outage, spreading into Utah County, with at least 10,000 homes out of power for a while.

Those without power for air conditioners or fans sweltered. The low temperature overnight reached only 71 degrees - 8 degrees lower than the record high minimum temperature for the date but still uncomfortable."It appears to be a failure of one of the splices" in an underground power line supplying the Dimple Dell Substation that caused the outage, said David Eskelsen, spokesman for Utah Power.

He believes the increased demand because of the hot weather played a role in the cable's breakdown but won't know for certain until technicians report more fully.

The failure tripped breakers at other substations, including those at 9000 South; Draper; and, in Utah County, Highland and Pleasant Grove. "There's probably easily 10,000 people" who were without power until the breakers could be reset, which took about half an hour.

Meanwhile, much of southeastern Sandy remained out of power. The affected area was from 400 West to 3900 East and from 10000 to 12450 South.

"Service was restored to most residents in the affected area by 6:30 a.m. However, as temperatures increase today, outages may again occur," Eskelsen warned Friday morning.

"When you get to July, we get a lot (of minimums) in the 70s, unfortunately," said William J. Alder, meteorologist in charge of the National Weath-er Office's Salt Lake regional office.

However, he held out some hope: "We've got a weak cool front that's coming through the Pacific Northwest and should be here midday tomorrow. Moisture should move north from Arizona, with scattered showers and thunderstorms throughout Utah on Friday and mainly in the state's eastern areas on Saturday."

Highs Friday should be mid- or upper-90s. On Saturday, they should dip slightly to middle or lower 90s. Saturday should be nicer, with the heat only reaching the mid-80s, Alder said.