A swift moving summer storm Friday night left more than a million in the Washington area without electricity Saturday morning, even as forecasters predicted temperatures would once again cross the 100 degree mark.

The powerful storm, which peppered the area with hundreds of lightning bolts, took down trees and power lines, even knocking out 911 call centers in Fairfax and Prince William Counties.

The National Weather Service issued an excessive heat warning for the entire Washington area until 9 p.m. Saturday, with heat indices expected to reach 110-115 degrees in the high humidity. Localities across the region opened cooling centers to make up for the lost air conditioning in many homes. Officials urged residents to find a cool place to stay and to check on elderly and at-risk neighbors.

But Fairfax officials warned residents to call before heading to county facilities to cool off: Some county buildings' power was also knocked out.

Officials urged Montgomery and Prince George's County residents to conserve water, since the power was out for the water utility, but said the water was safe to drink.

The Courthouse Metro station was closed Saturday morning due to the power outage.

The AT&T National golf tournament was closed to spectators because of the storm damage, organizers said. Saturday tickets will be honored Sunday, they promised.

Find regional storm cleanup updates and advice on what to do in the heat at http://www.capitalregionupdates.gov/.