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El Niño and La Niña are opposite phases of a natural climate pattern across the tropical Pacific Ocean. These two phases make up the El Niño Southern Oscillation (ENSO). ENSO pattern can be in one of three states; El Niño, La Niña, or Neutral phase. La Niña is a cold phase while El Niño represents the warm phase. These two phases can lead to significant differences in average sea-surface temperatures, winds, surface pressure and rainfall in the tropical Pacific.

While the Tennessee Valley is not located in the Pacific, these climate variations can still impact our local weather. When the ENSO is in the La Niña phase, there is the chance for warmer than average temperatures and an equal chance of above or below average precipitation. During the El Niño phase, there’s also an equal chance of seeing below or above average temperatures and precipitation. This means that there’s no signal to sway it strongly in either direction.

La Niña conditions have been intact since last August and are expected to continue into the upcoming winter. La Niña impacts are more pronounced in the winter season. When we experience this pattern, there are strong easterly trade winds resulting in strong surface winds. These strong winds lead to the upwelling of the cooler surface waters near the eastern Pacific to be pushed farther west. The result of this is cooler-than-average sea surface temperatures.

La Niña Conditions Forecast To Continue This Winter

The latest observations show that the negative subsurface temperature anomaly remains unchanged, reflecting the dominance of the below-average temperatures across the eastern Pacific. The Climate Prediction Center has a 91 percent chance of these conditions continuing through November and then a 54 percent by the start of the upcoming year.