Historic Oceanic Niño
Index (ONI) &
El Niño Winter - Spring Impacts
on United States Weather Patterns
Jan Null, CCM
The Oceanic Niño Index (ONI)
has become the de-facto standard that NOAA uses for identifying El Niño
(warm) and La Niña (cool) events in the tropical Pacific. It is
running 3-month mean SST anomaly for the Nino 3.4 region (i.e.,
Warm events are defined as 5 consecutive months above the .5o
anomaly. These are further broken down into Weak (with a 0.5 to 0.9
SST anomaly), Moderate (1.0 to 1.4) and Strong (> 1.4) events.
Winter Impacts (December, January, February)
Spring Impacts (March,
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