Historic Oceanic Niño Index (ONI) & El Niño Winter & Spring Impacts on United States Weather Patterns

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., 5^oN-5^oS, 120^o-170^oW). Warm events are defined as 5 consecutive months above the .5^o 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.

Weak events: 1963-64, 1969-1970, 1976-1977, 1977-1978, 1987-88
Moderate events: 1965-66, 1968-69, 1986-87, 1994-95, 2002-03
Strong events: 1957-58, 1972-73, 1982-83, 1991-92, 1997-98

click to enlarge

Winter Impacts (December, January, February)

click graphics to enlarge	All Warm Events	Weak	Moderate	Strong
oni		+0.5 to +0.9	+1.0 to +1.4	> +1.4
Years		1963-64, 1969-70, 1976-77, 1977-78, 1987-88	1965-66, 1968-69, 1986-87, 1994-95, 2002-03	1957-58, 1972-73, 1982-83, 1991-92, 1997-98
500-hPa Anomaly
Temperature Anomaly
Precipitation Anomaly

Spring Impacts (March, April, May)

click graphics to enlarge All Warm Events Weak Moderate Strong

oni +0.5 to +0.9 +1.0 to +1.4 > +1.4

Years 1964, 1970, 1977, 1978, 1988 1966, 1969, 1987, 1995, 2003 1958, 1973, 1983, 1992, 1998

500-hPa Anomaly

Temperature Anomaly

Precipitation Anomaly