April's unexpected warm-up sent temperatures surging to 101 degrees Monday in Dallas, rewriting weather records, triggering rolling electric blackouts and offering an early taste of what could be a hot, dry summer even by Texas standards.

JIM MAHONEY/DMNJulie Moore of Dallas seeks out some shade at Pioneer Plaza in Dallas. Monday's high of 101 degrees at Dallas/Fort Worth Airport set the record for the hottest-ever April temperature and was the third earliest 100-degree day ever.

So many air conditioners pumped out so much cool air across the sweltering state that the Electric Reliability Council of Texas - or ERCOT, which oversees and regulates power production - ordered utility companies to begin shutting off power to sections of their power grids on a rotating basis.

"With the temperatures as high as they are, there's a lot of demand on the system. It's an emergency situation at ERCOT," said Carol Peters, a spokeswoman for TXU Electric Delivery. "This is a planned procedure in response to an emergency."

Besides setting a record high temperature for the date, easily eclipsing the old record of 94 set in 1913 and equaled in 1925, Monday's high of 101 at Dallas/Fort Worth International Airport broke the record for the hottest-ever April temperature.

The heat will continue today, probably topping out in the mid-90s, said Troy Dungan, chief forecaster for WFAA-TV (Channel 8). A cool front arriving Wednesday morning should push temperatures down to the upper 70s and low 80s later this week and maybe bring some showers into the weekend.

"That's the same thing that stops thunderstorms from forming. It's so warm above us that the sun doesn't have to warm it. Instead, the sun's energy warms things closer to the surface."

The low-pressure systems that triggered tornadoes across the northern and central plains have pulled warm air north from the Gulf of Mexico and the Mexican deserts, further raising Texas temperatures, Mr. Shoemaker said.

"In March and April, we actually have a lot of generating equipment out of service for maintenance because it's usually cool this time of year," ERCOT spokeswoman Dottie Roark said. "Now we're getting close to needing the electricity we have available."

"They are truly rolling and random," DART spokesman Morgan Lyons said of the blackouts. "It's affected our signals system, but not our propulsion system."

Electricity demand in April rarely exceeds 40,000 megawatts, Ms. Roark said. But demand since Friday has been high, topping out Monday at more than 50,000 megawatts.

At the peak of the rolling outages, TXU Electric Delivery reduced its load by 380 megawatts, which is about equal to the energy needed to power 79,800 homes.

If the demand far exceeds supply capabilities and rolling blackouts are not used, "The system would start shutting down," Ms. Peters said. "You couldn't have power the next day. The equipment would be damaged."

Jackson Hewitt Tax Service in the 4000 block of Lemmon Avenue had to go a while without power - on tax deadline day no less. "When it went out, it was only for about 10 minutes," office supervisor Khrista Cartwright said.

Many people didn't know what to think when the lights went out. Because of construction in the area, few suspected the weather had caused the outages.

Mike Arroyos, who was driving on Lemmon Avenue near King's Road when the power went out, said he was nearly in a collision when the traffic lights stopped working.

Water temperatures in the far-off western Pacific indicate a La Niña weather pattern, "and that usually means a warmer than usual and drier than usual summer for us," Mr. Shoemaker said.

With North Texas lake levels already well below normal, water restrictions seem likely this summer, said Jim Parks, executive director of North Texas Municipal Water District, which provides water for 1.5 million people in 60 area cities.

The district declared Stage 2 drought conditions in January, calling for voluntary conservation. But officials say a Stage 3 drought is likely by summer, with mandatory water restrictions, including a ban on watering lawns from 10 a.m. to 6 p.m. and watering limits of 1 inch a week.

"We should be cooler beginning Wednesday when that cold front passes through," Mr. Shoemaker said. "And beginning Thursday and running through the weekend, there's a decent chance of rain off and on.

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