La Niña has officially started: What happens next

AUSTIN (KXAN) -- The Climate Prediction Center announced Thursday that La Niña has officially started. A detailed analysis found La Niña began in December 2024 with a weak La Niña favored during the rest of this winter.

La Niña is the cool phase of ENSO (El Niño-Southern Oscillation) that is marked by sea-surface water temperatures 0.5ºC below the climatological average in a key area of the eastern Pacific.

Those water temperatures reached that key metric in December marking the long-awaited arrival of La Niña.