Flash Flood — Riverside, California

2025-09-18 · near Eagle Mtn, Riverside, California

Event narrative

CA-177 closed in both directions between I-10 and CA-62 due to flooding, with at least one car stuck in the floodwaters. No injuries reported.

Wider weather episode

The combination of an upper-level low off the CA coast and the remnants of Tropical Cyclone Mario resulted in a significant moisture increase with PWATs rising to 1.5 on the 17th and upwards of 1.8-2.0 on the 18th. Thunderstorms on the 17th were concentrated mainly across the higher terrain areas of southeast CA, mainly across the Chocolate Mountains, while on the 18th, the activity was more widespread as upper-level forcing from the combination of the upper-level low and the remnants of Tropical Cyclone Mario was maximized. With MLCAPE values maxing out at 1500 J/kg along with the abundant moisture, the thunderstorms were efficient rain producers, resulting in instances of flash flooding. DCAPE values ranging between 1000-1200 J/kg also supported instances of severe damaging wind gusts.

View location on OpenStreetMap → (34.0268, -115.2575)

Source: NOAA Storm Events Database, event_id 1293016. Narrative written by the NWS forecast office that issued the report.