U.S. precipitation patterns for every La Niña winter since 1950

When the natural climate pattern La Niña develops in the tropical Pacific Ocean, it can affect areas thousands of miles away, including the United States. The effects are strongest in Northern Hemisphere winter. Check out these maps to see if La Niña has a reliable impact on the precipitation where you live.

These maps show December-February precipitation (rain and snow) across the contiguous United States compared to the 1991-2020 average during all 24 La Niña winters since 1950. Maps are sorted from top left to bottom right based on the strength of the La Niña event in December-February. Places that were wetter than average over the winter are blue-green; places that were drier than average are brown. (Additional technical details are at the bottom of the post.)

There are a few important things you have to remember about the influence of La Niña (and El Niño) on U.S. seasonal climate. 

1. No two events are exactly the same. 
2. Strong events don't guarantee strong impacts; they just make it more likely that some level of impacts will occur. 
3. La Niña and El Niño have a weaker influence on temperature than precipitation.

The typical U.S. impacts of La Niña are warmer- and drier-than-average conditions across the southern tier of the United States, colder-than-average conditions across the north-central Plains, and wetter-than-average conditions in the Pacific Northwest stretching into northern California. "Typical" doesn't mean "always," though, as the maps show. 

For example, Florida was drier than average in 5 of the 6 strong La Niña winters and in 12 of the 13 winters of at least moderate strength. Most of Texas was drier than average in 4 of the 6 strong La Niñas. Meanwhile, large parts of northern California, Oregon, and Washington were wetter than average in 5 out of 6 strong La Niña winters, as was the Ohio Valley in the East. 

These “failures” of the typical pattern happen because La Niña is never the only thing that influences the climate over the United States during the winter. Other climate phenomena, such as the Arctic Oscillation or the Madden Julian Oscillation, as well as the random variability of weather and climate also play a part in how a winter turns out. 

This inherent variability is why climate forecasters always talk about seasonal climate outlooks in terms of "odds," "chances," or "probabilities"—not guarantees. You can read more about how to understand and use probabilistic forecasts in our ENSO Blog archives. 

Technical details

A winter was considered a "La Niña winter" if it was colored blue in NOAA's Relative Oceanic Niño Index (RONI) table. Years are sorted from strongest La Niña  (top left) to weakest (bottom right)‚ based on the RONI value observed during December–February. For this graphic, winters with RONI values at or below -1.5 were ranked as strong, winters with RONI values between 1 and 1.5 were ranked as moderate, and events with RONI values less than -1 were ranked as weak. NOAA has recently started categorizing events with a peak RONI Index of -2 and lower as "very strong." However, none of the strong events met that threshold in the December-February season.  

Maps by Climate.us, based on NOAA nclimgrid data.