"We believe it was weather-related, but we don't know for sure," utility spokesman Mick Shutt said.

At 12:15 p.m., power went off for 11,315 business and residential customers, including the Vancouver Mall neighborhood. Traffic lights also were inoperative, although police dispatchers said motorists managed to avoid any accidents.

Shutt said utility workers may never know the exact cause of Wednesday's power failure.

"All they did is reset the breakers and turn it back on," he said.

Utility workers know they lost power on a transmission line serving four substations in the Hazel Dell and Minnehaha areas north of Vancouver. Shutt said a tree limb might have dropped on the line long enough to short it out, but then bounced away before causing any noticeable damage.

A balky switch failed at a Bonneville Power Administration substation in the same area in June, cutting power to about 5,000 residential and business customers from the BPA's Ross Complex in Minnehaha to downtown Vancouver.

BPA spokesman Ed Mosey said Wednesday that Bonneville was not to blame this time, and Shutt concurred.

A downpour coincided with the power failure, suggesting a tree limb sagged or broke onto the transmission line during the unsettled weather. Crews restored electricity in blocks, Shutt said, with the final block coming on by about 1:30 p.m.