And on the 12th day, the mercury dropped.

A cold front moved into the Washington area Sunday night and early Monday, bringing thunder, lightning and cooling rains that ended 11 days of oppressive, excessive heat.

Predictions of fist-size hail and winds of up to 70 mph failed to materialize, and there was no repeat of the massive power outages that crippled parts of the District and its suburbs starting on June 29.

Instead, a light rain was falling as of 8 a.m., and the thermometer read 74 degrees — a drop of nearly 30 degrees from midday Sunday. Metro officials said Green Line trains were running normally after a heat-related derailment Friday, and all weather-related restrictions had been lifted for the morning commute.

Dominion Power said 23,000 customers lost service about 6:15 p.m. Sunday after storms and lightning struck in Northern Virginia, but the utility had reduced the number of outages to about 3,500 by 8 a.m. Monday.

Pepco reported only about 300 outages in the District, Montgomery County and Prince George’s County by 8 a.m.

And forecasters predicted temperatures in the low to mid-80s all week, with thunderstorms possible every day.

After the thermometer hit 105 on Saturday— one degree short of the all-time heat record — relief started to come as early as Sunday morning, when the temperature inched down to 102.

But who could tell? It still seemed as if the region had been buried alive in heat, as if the air was an enemy. Many felt like they were trapped indoors; those who ventured outside planned movements between air-conditioned venues the way generals plan island-hopping campaigns.

The heat wave had forced the cancellation of some outdoor events; sent people to pools, theaters, libraries or other air-conditioned ­oases; and even bent Metro’s steel tracks enough to derail a Green Line train.

By 9 p.m. Sunday, the temperature at Reagan National Airport was 84 degrees — 18 degrees below the day’s high.

Meanwhile, the front triggered a severe storm in Spotsylvania County, Va., that damaged three commercial buildings and a house, injuring at least seven people in a neighborhood at the county’s northeastern edge, said Mark Kuechler, a county fire and rescue spokesman. Jared Klein, a National Weather Service meteorologist, said a decision would probably be made Monday on whether to survey the damage to determine whether it was caused by a tornado.

Earlier Sunday, a 20-foot section pavement buckled in the heat on eastbound Route 50 in the Bowie area. Some vehicle damage was reported when the incident first occurred, state police Sgt. John Revel said.

For much of the weekend, service was halted on part of the Green Line, after the derailment on Friday that Metro officials said was caused by the heat. On Sunday night, Metro restored service on a single track between the Fort Totten and Prince George’s Plaza stations. Full service was restored for Monday morning.

While some exasperated residents — including a Bethesda family menaced by what appeared to be a live wire down near their home — were still contacting Pepco and other utilities about restoring power lost more than a week ago, regional officials were beginning to assess the financial impact of the derecho and the heat wave.

Fairfax County Board of Supervisors Chairman Sharon S. Bulova (D) said she expected to see higher overtime costs and other expenses caused by having to operate cooling centers. Virginia officials are also seeking answers from Verizon about the loss of 911 service after the storm.

Lon Anderson, spokesman for AAA Mid-Atlantic, said it is unclear what impact the historic chain of extremely hot days has had on the region, but he suspects that it has reduced the number of travelers. “Because of the heat, people who might have wanted to come here didn’t,” Anderson said.

By 3 p.m. Sunday, the temperature at Reagan National Airport had climbed to 102, setting a new daily record, according to Jason Samenow, meteorologist for The Washington Post’s Capital Weather Gang. It also made for the fourth-straight day of 100 degrees or higher, matching a record-long streak set in July 1930.

The record-breaking heat wave has been linked to 10 deaths in recent days in Maryland and Virginia. It also complicated efforts to recover from the wreckage of an unusual storm that knocked out power to hundreds of thousands of people.

Christina M. Hartman, 30, who lives in Bethesda, said Sunday that Pepco still had not dealt with a power line in her yard — even though an electrician who installed a cable at her home on Thursday said that he thinks the downed line is carrying electricity. And she has had trouble getting anyone from the utility to come check it out.

“They say they have a ticket open,” Hartman said.

There were no reported heat-related deaths in Virginia from the weekend’s near-record highs, according to Maribeth Brewster, a Virginia Department of Health spokeswoman. Maryland’s Department of Health and Mental Hygiene reported three heat-related deaths over the weekend, spokeswoman Karen Black said. District officials could not be reached.

On Sunday, with temperatures again in the triple digits, Metro was operating with a 35 mph maximum speed limit on all above-ground tracks, and additional teams of inspectors were walking the rails looking for possible problems, Metro spokesman Dan Stessel said.

All heat-related restrictions were lifted on Monday, after the enormous heat dome that had settled over the eastern two-thirds of the country for the past two weeks was broken, allowing the dip in the jet stream to move east and deliver cooler air from the north.

“We’re not going to see a return of record heat anytime soon,” Samenow said.

For the next week, he said, high temperatures should reach the mid- to upper 80s, close to normal if not a bit below.

“I don’t even see us hitting 90 this week, which is good,” Samenow said.

Hamil R. Harris, Katherine Shaver and Marissa Evans contributed to this report.