National Weather Service United States Department of Commerce
El Niño-Southern Oscillation (ENSO) effect on
Winter Weather across West Central and Southwest Florida

El Niño and La Niña are opposite phases of a natural climate pattern across the tropical Pacific Ocean that swings back and forth every 3-7 years on average. Together, they are called ENSO (pronounced “en-so”), which is short for El Niño-Southern Oscillation.

The ENSO pattern in the tropical Pacific can be in one of three states: El Niño, Neutral, or La Niña. El Niño (the warm phase) and La Niña (the cool phase) lead to significant differences from the average ocean temperatures, winds, surface pressure, and rainfall across parts of the tropical Pacific. Neutral indicates that conditions are near their long-term average.

Typical Wintertime Pattern during El Niño
      Typical Wintertime Pattern during La Niña

During an El Niño Winter the southern tier of Alaska and the U.S. Pacific Northwest tend to be warmer than average, whereas the U.S. southern tier of states—from California to the Carolinas—tends to be cooler and wetter than average. Meanwhile La Niña typically brings above-average precipitation and colder-than-average temperatures along the northern tier of the U.S., along with below-average precipitation and above-average temperatures across the South.

An analysis of the 300 millibar (≅30,000 feet) wind speeds, the appoximate location of the jetstream, during the different ENSO phases depicts rather well how the location of the jetstream shifts with the stronger winds (red areas in image below) further south during El Niño and further north during La Niña.
300 mb Wind Speeds during different ENSO phases300 mb Wind Speeds during different ENSO phases
However, there are other climate patterns, such as the Madden-Julian Oscillation and Arctic Oscillation (AO), that can also play a role in determining winter weather. For example, the AO influences the number of arctic air masses that intrude into the U.S., but its predictability is limited to a couple of weeks. More local information about how the AO effects the weather across the Florida peninsula can be found at Arctic Oscillation: Impacts on West Central and Southwest Florida

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