Flash Flood — Riverside, California

2018-09-30 · near Mortmar, Riverside, California

Event narrative

Thunderstorms with very heavy rain developed across portions of eastern Riverside County during the evening hours on September 30th. The stronger storms produced intense rain that led to flash flooding to the southwest of Joshua Tree National Park and to the north of the Salton Sea. At 1925PST (2025 PDT) the California Highway Patrol reported that Box Canyon Road was closed at the Mecca Copia Trail due to flash flooding. Significant impacts were reported to have occurred further downstream. Major damage was reportedly done to the Box Canyon Road forcing the road to be closed for days. It was also reported that a man was swept to his death driving along Box Canyon Road between Interstate 10 and Highway 111. He was returning from a camping trip in Joshua Tree National Park. His damaged car was found by the road later the next day with no trace of the man to be found. A Flash Flood Warning was issued for the area at 1909MST and it remained in effect until 2215MST.

Wider weather episode

Deep tropical moisture started to spread north and into far southeast California during the day on September 30th; the moisture spread into the area ahead of Hurricane Rosa and led to the development of isolated thunderstorms. Due to the tropical nature of the moisture, the storms that developed produced very heavy rain which led to an episode of flash flooding in eastern Riverside County, to the southwest of Joshua Tree National Park and just north of the Salton Sea. At 1925PST, the California Highway Patrol indicated that Box Canyon Road was closed at Mecca Copia Trail due to flash flooding. The patrol indicated that there were significant flooding issues further downstream with major damage done to Box Canyon Road. It was also reported that a man was swept off of Box Canyon Road and to his death due to flash flooding of a large wash running across the road, between Interstate 10 and Highway 111.

View location on OpenStreetMap → (33.5614, -115.8674)

Source: NOAA Storm Events Database, event_id 779523. Narrative written by the NWS forecast office that issued the report.