Historic Oceanic Niño Index (ONI) &
La Niña Winter 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 the running 3-month mean SST anomaly for the Nino 3.4 region (i.e., 5oN-5oS, 120o-170oW).  Cold events are defined as 5 consecutive months at or below the -0.5o 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 (≤ -1.5) events.

Weak events:  1956-1957, 1961-1962, 1971-1972, 1974-1975, 1983-1984, 1995-1996, 2000-2001 
Moderate events:  1950-1951, 1954-1955, 1964-1965, 1969-1970, 1984-1985
Strong events:  1955-1956, 1973-1974, 1975-1976, 1988-1989

  


click to enlarge

Winter Impacts (December, January, February, March)

click graphics to enlarge All Cool Events   Weak   Moderate   Strong
oni     - 0.5 to - 0.9   -1.0 to -1.4   ≤ 1.4
Years     1956-1957, 1961-1962, 1971-1972, 1974-1975, 1983-1984, 1995-1996, 2000-2001   1950-1951, 1954-1955, 1964-1965, 1969-1970, 1984-1985   1955-1956, 1973-1974, 1975-1976, 1988-1989
500-hPa Anomaly      
               
Temperature Anomaly          
               
Precipitation Anomaly              

 
       


Copyright © 2007, Golden Gate Weather Services. 
Reproduction in full or part is prohibited without permission.