SAN DIEGO (CNS) - Late-summer thunderstorms lashed the East County highlands with downpours, lightning and stiff winds Thursday, causing scattered flash flooding and downing a few trees and power poles.

Fueled by high temperatures and monsoonal moisture out of Mexico, north-moving thunderheads developed over the county's mountains in the early and mid-afternoon, according to the National Weather Service.

The towering cloud banks generated scores of lightning strikes and periods of heavy rain that led to back-country flash flooding around Palomar Mountain, Cuyamaca State Park and nearby areas, the federal agency reported.

Pea-sized hail fell near Julian and Pine Valley, where winds gusting up to 60 mph also toppled trees and utility standards, NWS meteorologist Brett Albright said.

Measurable precipitation fell in some locales, including Oak Grove, which received 1.23 inches; Lake Cuyamaca, 0.8 of an inch; Pine Hills, 0.27; and the Campo area, 0.46. A number of other spots got a few hundredths of an inch of moisture.

The storm activity was diminishing by late afternoon, though similar -- if somewhat less intense -- conditions were expected to return to eastern San Diego County on Friday, Albright said.

Over the weekend, the region should enjoy a slight cooling trend and some relief from the recent spike in humidity levels, the weather service predicted.