La Ni?a: What It Means for California’s Weather and Water

National Oceanic and Atmospheric Administration scientists recently forecasted a 70% chance that La Ni?a develops between August and October, and a nearly 8 in 10 chance of La Ni?a this winter.?

On the heels of a strong El Ni?o year, whose effects were a shadow of what many expected, understanding the potential impacts of La Ni?a is crucial for Californians.

La Ni?a and Its Impact

The periodic fluctuation of sea surface temperatures in the Pacific is referred to as ENSO (El Ni?o-Southern Oscillation) and occurs in two phases: El Ni?o (warmer sea surface temps) and La Ni?a (cooler).

This natural occurrence can significantly influence global weather patterns. California has a particular interest in these patterns due to the state’s precarious water situation, as both El Ni?o and La Ni?a impact annual precipitation.

La Ni?a events are often associated with drier conditions in California. Three of the driest years on record in California—2020 through 2022— coincided with La Ni?a and were marked by severe drought and unprecedented water restrictions.

However, this pattern is not guaranteed, as La Ni?a’s influence on precipitation is complex and varied.? For example, in the 2022-23 water year, despite La Ni?a conditions similar to the previous dry year, California experienced above-normal precipitation.

Even more noteworthy, the 2016-17 water year, the wettest year on record for California, was during a weak La Ni?a.??

While La Ni?a can load the dice for certain weather patterns, it does not guarantee a specific outcome.?

Atmospheric Response to La Ni?a

Recent research by Dr. Jiang of UCLA underscores that while sea surface temperatures are a significant factor, they only explain about 25% of the year-to-year variability in California’s precipitation.

The remaining 75% is largely determined by atmospheric circulation patterns that are independent of ENSO.?

These findings highlight a crucial gap in our ability to predict California’s winter precipitation: while ENSO-related patterns provide some insight, they account for only a quarter of the variability.? Furthermore, dynamic models are unable to reliably predict these ENSO-independent circulation anomalies, explaining their limited predictive skill for California winter precipitation.??

A New Approach: Weather Tools’ CAP Forecast

The California Annual Precipitation (CAP) forecast offers a different approach. At Weather Tools, our CAP forecast utilizes a proprietary model that does not rely on historical climate patterns. This proven method has enabled us to deliver accurate water year precipitation forecasts for eight consecutive years, regardless of climate forcing.

The CAP forecast has consistently demonstrated its accuracy, even during La Ni?a years. For instance, in the 2022-23 water year referenced above, our forecast predicted precipitation amounts ranging from 20-40% above the state average. National Weather Service data confirmed that actual precipitation was 43% above normal, showcasing the robustness of our model.?

In water year 2016-17, a weak La Ni?a, the CAP forecast predicted precipitation greater than 40% above normal.? Remarkably, the total precipitation for the water year was 64.1% above normal.?

Conversely, the National Weather Service seasonal precipitation outlook discussion for December 2016 to February 2017 called for dry conditions primarily due to the influence of La Ni?a.?

Preparing for La Ni?a: Looking Ahead

As we transition from the El Ni?o-dominated 2023-24 water year to a likely La Ni?a-influenced 2024-25, it’s crucial to remember that La Ni?a accounts for only a fraction of the overall precipitation outcome.

The CAP statistical model sidesteps this challenge with our novel approach.

Issued in the first week of November, the CAP forecast has proven its accuracy, offering precise water year predictions regardless of climate forcing.

This approach ensures that Californians are better prepared for the potential impacts of La Ni?a, whether wet or dry.

Interested in the complete picture for water year 2024-25??

Learn more about the CAP forecast here, or contact us directly at [email protected] or by calling 530-774-5475.