SAN DIEGO -- A moist and unstable air mass brought periods of heavy rain and lightning to the San Diego area Monday, causing scattered flooding and forcing the closure of an East County highway.

The sultry, unsettled conditions prompted the National Weather Service to issue a flash-flood watch, effective from the midmorning through early evening.

In the late morning and afternoon, banks of thunderheads let loose with downpours across the region's eastern and northern reaches.

Between 11 a.m. and 5 p.m., the cloudbursts dropped 0.75 inches of rain in Ranchita, west of Borrego Springs; 0.28 in Cuyamaca; 0.24 in Julian; and 0.04 at Sutherland Dam, west of Santa Ysabel, and in Tierra del Sol, east of Campo.

About 4:30 p.m., heavy showers forced the closure of a stretch of State Route 78 just east of Yaqui Pass Road in Anza-Borrego State Park, according to the California Highway Patrol.

Caltrans crews were able to reopen the east-west roadway shortly before 6:30 p.m., the CHP reported.