NOAA Forecasts Heavy Winter Rainfall for California
Federal forecasters predict above-average precipitation for Southern California through next June.
Updated on Sept. 18, 2026 in Forecasts
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The National Oceanic and Atmospheric Administration has issued outlooks indicating a high probability of above-average winter rainfall across Southern California. These conditions coincide with several key regional reservoirs already nearing their total storage capacity.
Why it matters
High reservoir levels combined with projected heavy precipitation increase the risk of water management challenges across Southern California. Managing these inflows safely remains a priority as the region transitions into the new water year.
Castaic Lake and Lake Casitas are both at 95 percent capacity, while Diamond Valley Reservoir is at 97 percent capacity. These figures significantly exceed historic averages, with Diamond Valley sitting at 129 percent of its typical level.
The players
National Oceanic and Atmospheric Administration
This federal agency is responsible for monitoring climate patterns and issuing long-term atmospheric forecasts for the United States.
Climate Prediction Center
A branch of the National Weather Service, this body provides official seasonal climate outlooks and monitors the El Niño-Southern Oscillation cycle.
The details
Reservoir managers typically draw down water levels every winter to create necessary storage space for expected rain. While Diamond Valley Reservoir is an off-stream facility filled via pipelines, other facilities must prepare for potential high inflows as a super El Niño pattern strengthens.
Timeline
September 18, 2026: Current reservoir capacity levels were reported.
October 2026: The new water year begins.
November 2026: The window for above-average precipitation probability begins.
December 2027: The seasonal outlook period concludes.
Seasonal Patterns
The transition toward a super El Niño cycle follows historical climatological patterns that correlate with increased rainfall across the Southern California region. This shift updates the previous, more moderate projections for winter weather stability in the state.
Residents should monitor local water agency updates for potential releases or drainage operations near major reservoirs. Preparedness plans for heavy winter weather should be reviewed before the precipitation probability increases in November.
The takeaway
Maintaining sufficient storage capacity in reservoirs is critical to preventing flooding during periods of intense, concentrated rainfall. Homeowners in low-lying areas should ensure their drainage systems are clear to mitigate risks during the upcoming wet season.
Further reading
For more on expected weather trends, visit the Forecasts section.
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