La Niña Expected to Develop This Fall. Here’s What That Means for Northern California.
Northern California residents may see a shift in weather patterns this fall as scientists at the National Oceanic and Atmospheric Administration (NOAA) predict the development of a weak La Niña. According to a forecast update, there is a 71% chance that La Niña conditions will establish by October or November and persist through early next spring.
La Niña events are characterized by an increase in easterly trade winds over the equatorial Pacific, which pushes warm surface water westward and brings colder water to the surface in the eastern Pacific. This shift in ocean temperatures can influence seasonal weather across North America.
However, the impact of a weak La Niña on Northern California’s winter precipitation has been historically inconsistent.
Since 1952, twelve weak La Niña events have occurred, showing varied outcomes for Sacramento’s rainfall. Three of those years recorded near-average precipitation (86%-100%), while three saw above-average rainfall (100%+).
Last year during a weak La Niña, Sacramento received 144% of its average annual rainfall. Conversely, six years experienced below-average precipitation, with the 1971-1972 water year seeing only half of the average rainfall.
The variability extends to rain and snow in the Northern Sierra as well. Out of the twelve weak La Niña events, five years saw above-average rain and snow, while five experienced below-average precipitation, as measured by the 8-station index for the Northern Sierra.
The past two winters have brought above-average rain and snow to the region. The winter of 2022-2023 was marked by a weak La Niña, while last winter showed no clear signs of either La Niña or El Niño conditions.
As we look ahead to the upcoming winter, Northern California residents should prepare for a range of potential weather scenarios, keeping in mind the unpredictable nature of weak La Niña events.
