Update 2:15 p.m. A severe thunderstorm warning has been issued for southwest San Bernardino County, the city of Redlands, northwest Riverside County, and the city of Moreno Valley through 2:45 p.m.
National Weather Service radar indicated a thunderstorm capable of producing quarter-size hail and damaging winds in excess of 60 miles per hour.
At 1:42 p.m. the storm "was extended from Moreno Valley to just south of Redlands . . . and moving northwest at 10 miles per hour," the Weather Service advised.
Other locations in the warning area included but were not limited to Loma Linda, Colton and Mentone.
Another developing storm was just east of Lakeview, about five miles north of Hemet.
Posted 2 p.m. Thunderstorm activity prompted flood advisories and warnings Thursday afternoon in Mill Creek Canyon northeast of Redlands and Loma Linda.
A flash flood warning was in effect until 2 p.m for south central San Bernardino and extreme northwest Riverside counties.
National Weather Service radar indicated heavy rain capable of producing flash flooding, and a thunderstorm with excessive rain was expected to remain over Forest Falls and Mill Creek.
Strong winds, hail and lightning capable of starting fires were also possible.