The cool air returned to San Francisco last night. When I took this picture this morning about 8:00 a.m., fog masked the skyline and Twin Peaks, but a ray of sun illuminated the inner Mission District. Taken from Bernal Heights.

Meanwhile, more than 100 fires were caused by lightning last night in counties north of the city, and inland areas still expect 100-degree temperatures, though cooling is expected to help firefighters in Napa and Solano counties.

I wouldn’t drop my guard just yet, but after people in Potrero Hill and Bernal Heights were plagued by a spate of muggings over the last several weeks, three men were arrested last night after an incident on Potrero Hill. Police said the men may be linked to the previous incidents.