SAN DIEGO — A flash flood warning was issued Wednesday afternoon for Pine Valley and Mount Laguna, according to t he National Weather Service, San Diego.

The severe storm that developed near Mount Laguna produced 60 MPH wind gusts, penny sized hail and heavy rain, according to News 8's Chief Meteorologist Karlene Chavis. 

Storms near Julian were so strong, residents were warned to remain indoors.

Mountain areas also see thunderstorm activity Wednesday morning, NWS meteorologist Greg Martin said.

A high pressure system hanging over the Four Corners region is causing our heat wave while monsoonal moisture from Mexico is generating precipitation. Some light rain could accompany thunderstorms today before heavier showers are expected on Thursday, Martin said.

A chance of thunderstorms will continue through Friday evening in the mountains and through Thursday evening in the deserts, while the thunderstorm activity is expected to clear out of coastal and inland valley areas by Wednesday night.

The chance of measurable precipitation has been set at 20 percent today for the inland valleys, coastal areas and the deserts, according to the NWS. There is a 50 percent chance today in the mountains.

High temperatures Wednesday are expected to reach 89 near the coast and inland, 93 in the western valleys, 98 near the foothills, 96 in the mountains and 111 in the deserts.

The heat wave is expected to peak on Saturday, when temperatures in the deserts could reach 116, forecasters said.