How do El Niño and La Niña differently affect U.S. winter temperature and snowfall patterns?
This fact-check may be outdated. Consider refreshing it to get the most current information.
Executive summary
El Niño and La Niña are opposite phases of ENSO that shift the Pacific jet stream and therefore alter U.S. winter temperature and snowfall patterns: La Niña typically favors colder-than-normal winters and increased precipitation (rain or snow) across the northern U.S. and drier, warmer winters in much of the South, while El Niño tends to push the jet stream south bringing wetter winters to the southern U.S. and milder conditions in parts of the north [1] [2] [3]. Recent reporting and government outlooks show forecasters expected La Niña to influence the 2025–26 winter—generally meaning a colder, snowier north and a drier, milder South—though many outlets stress the event was likely weak and regional outcomes vary [4] [5] [2].
1. How the Pacific drives U.S. winters: jet-stream steering and the ENSO lever
ENSO shifts east‑central tropical Pacific sea surface temperatures; El Niño is warm, La Niña is cool. Those ocean changes reorganize the Pacific jet stream: El Niño tends to move the jet south and east, La Niña moves it north and weakens it over the eastern Pacific—this steering explains the broad U.S. temperature and precipitation differences between the two phases [1] [6].
2. La Niña’s typical winter fingerprint: colder north, warmer south, snow where moisture meets cold
A classic La Niña winter brings colder-than-normal weather across much of the northern U.S. and warmer-than-normal conditions in the South, with more precipitation in the Pacific Northwest and northern states and below-average precipitation across the southern tier [1] [2] [3]. That combination often increases snowfall potential in the northern plains and Rockies when cold air and moisture coincide; several news analyses flagged more snow for the Rockies as a common La Niña outcome [7] [8].
3. El Niño’s contrasting signature: wetter south, milder north, Southeast snow surprises
El Niño typically pushes the Pacific jet farther south and east, producing wetter-than-average winters across the southern U.S. and generally milder conditions in some northern areas [1]. El Niño winters can also cause unusual snowfall in the Southeast in certain years, undercutting the simple “north cold, south warm” story (p1_s14 notes El Niño links to southeast snow).
4. Forecast probability and strength matter: weak events give weaker, patchier signals
Forecasters repeatedly emphasize event strength and timing. A weak La Niña or a late start weakens the ENSO signal and reduces the reliability of the “typical” regional impacts; NOAA and climate analysts warned that weak La Niña conditions are less likely to produce the textbook outcomes [9] [5]. For winter 2025–26, multiple outlets called the La Niña expected to be relatively weak or short‑lived, which lowers confidence in a uniform national pattern [5] [10].
5. Real winters deviate: recent seasons show important caveats
Journalistic reviews of recent winters show substantial departures from the textbook pattern: the 2024–25 season, while influenced by La Niña, produced pockets of both excess and deficit snowfall, including big snow shortfalls on the I‑95 corridor and surprising snowfall in Tennessee Valley and mid‑Atlantic regions—illustrating that ENSO is a dominant factor but not a deterministic one [3] [7].
6. Regional takeaways for planners and the public
If La Niña is present, prepare for an increased chance of colder and potentially snowier conditions across northern states and more active storm tracks in the Pacific Northwest and northern Plains; southern states should plan for a higher likelihood of milder, drier conditions and below‑normal precipitation [2] [1]. However, multiple outlets stress consulting local forecasts and short‑range model guidance because ENSO provides seasonal tendencies, not day‑to‑day predictions [6] [11].
7. Sources, disagreements and hidden caveats
Government sources and mainstream meteorology (NOAA/Climate.gov) present the mechanism and typical impacts clearly [6] [1]. News coverage and private forecasters largely agree on the broad pattern for La Niña winters but diverge on the magnitude and regional certainty—many warn that the 2025–26 La Niña was expected to be weak, which reduces predictive power [4] [2] [5]. Some private analyses assign higher probabilities to La Niña persistence; others emphasize rapidly changing subsurface ocean signals and possible transitions, so readers should view seasonal outlooks as probabilistic guidance, not guarantees [11] [10].
Limitations: available sources summarize patterns and recent forecasts but do not provide deterministic maps for every locality; local impacts depend on jet‑stream position, other climate modes (like the PDO), and storm‑by‑storm dynamics—factors described in the sources but not resolved to a city‑level certainty [12] [10].