Winter precipitation patterns during each of the 20 strongest La Niña episodes since 1950. The strength is measured by the December–February Oceanic Niño Index (ONI), which is three-month average surface temperature departure from normal in the Niño 3.4 region. The December–February ONI for each episode is shown in parentheses (units of °C) above each map. Dark green colors indicate much wetter than normal conditions, and dark brown colors indicate much drier than normal conditions. The strongest La Niña episode is on the top left, and the weakest of the 20 episodes is on the bottom right. Maps by NOAA Climate.gov, based on NCEI climate division data provided by the Physical Sciences Division at NOAA ESRL.