Monday, December 22, 2025

Flood Watch Issued for Pasadena and Altadena as Atmospheric River Approaches

National Weather Service

A broad Flood Watch that includes Pasadena and Altadena will take effect Tuesday afternoon as a moderate to strong atmospheric river brings the potential for heavy rainfall and widespread urban flooding, according to a National Weather Service advisory issued Sunday.

The Flood Watch, announced by the National Weather Service’s Los Angeles/Oxnard office, remains in effect from Tuesday afternoon through Wednesday evening. Forecasters said flooding caused by excessive rainfall “continues to be possible” across the region.

Officials warned that excessive runoff may result in flooding of rivers, creeks, streams and other low-lying or flood-prone locations. The advisory also noted the potential for mud and debris flows across all foothill and mountain areas. Both Altadena and Pasadena are included in the Los Angeles County San Gabriel Valley zone listed in the watch.

The Weather Service said the incoming system is expected to deliver high rainfall rates as it moves across Southwestern California. The agency described the storm as a “moderate to strong atmospheric river,” with widespread urban flooding possible.

A separate Flood Watch was also issued for the Malibu Coast, including Malibu and Pacific Palisades, covering the same Tuesday-through-Wednesday timeframe.

Residents are urged to monitor later forecasts and remain alert for possible Flood Warnings. According to the Weather Service statement, those living in areas prone to flooding should be prepared to take action should flooding develop.

More information on flood safety is available at the National Weather Service website: http://www.weather.gov/safety/flood.