National Weather Service United States Department of Commerce

Marginal Risks of Severe Storms on the Central Plains; Flash flooding on the Northern Plains; Frost & Freeze Warnings in portions of the West & Northeast

A storm system developing across the Plains may cause locally severe weather in western Kansas and southwestern Nebraska today, with isolated flash flooding possible in portions of eastern Montana and western North Dakota. Frost and Freeze Warnings are in effect for portions of the central Rockies and central Appalachians tonight into Friday morning. 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