National Weather Service United States Department of Commerce

Cold, Wintry Blast to Impact the Eastern States; Air Quality Issues Continue in the Northwest

The Arctic Storm that has impacted the Central U.S. will now move into the East with the potential for record cold temperatures, gusty winds, and widespread areas of snow or rain and snow mixed. Heavy lake effect snows will continue for some Great Lakes areas. Meanwhile, in the West, record warmth continues; and stagnant air remains entrenched in the Northwest. Read More >

ENSO Indices


ENSO Regions


Southern Oscillation Index (SOI)
standardized anomaly of the mean sea level pressure difference between Tahiti and Darwin

  • traditional ENSO index

  • correlates strongly with SST anomaly indices

NOAA Oceanic Niño Index (ONI)
sea surface temperature anomaly index for Niño 3.4 (5°N to 5°S, 170°W to 120°W)

  • onset of El Niño declared when Niño 3.4 anomaly exceeds +0.5°C for 3-month period

  • to be "full-fledged" El Niño (or La Niña), onset conditions must be met for 5 consecutive 3-month periods

Japanese Meteorological Agency ENSO Index (JMA)
sea surface temperature anomaly index for Niño 3 (4°N to 4°S, 150°W to 90°W)

  • less noisy than traditional SOI and more vigorous than NOAA ONI

  • anomalies must exceed 0.5°C for 6 consecutive 5-month periods

Multivariate ENSO Index (MEI)
weighted anomaly average of 6 meteorological variables in the tropical Pacific

  • sea surface temperature

  • sea level pressure

  • surface air temperature

  • components of surface wind

    • zonal component

    • meridional component

  • total cloudiness fraction of the sky