Interpretation of the Data

El Niño and La Niña events play a critical role in autumn through spring flows. El Niño is referred to as the warming of the equatorial Pacific Ocean along and east of the dateline while La Niña is referred to as the cooling of the equatorial Pacific Ocean along and east of the dateline.

The composite El Niño indicates flows along the entire reach of the Ohio River tend to be below normal while the composite La Niña indicates flows along the entire reach of the tend to be above normal.

However, research (Noel, Changnon, 1997) indicates it is not that helpful to use a composite for El Niño or La Niña unless you are in specific parts of the country like the Upper Midwest or Texas where signs are consistent. It is important to look at the strength of the event. During weak to moderate El Niño events, flows tend to be below normal while during strong events flows tend to be above normal. This opposite effect is also true of La Niña events. During weak to moderate La Niña events, flow tends to be above normal while during strong events, flows tend to be below normal.

Therefore, it is very important to not only know what type of event you are have, but the magnitude and intensity of that event. Weak to moderate events in the Pacific Ocean do not have nearly the global impact that the strong events have. It makes sense that weather closer to home play as much or more of a role during the weak to moderate events, such as the North Atlantic Oscillation (NAO). However, during the strong ENSO events, they tend to dwarf other weather factors closer to home form autumn to spring.

This link to a ENSO presentation provides graphs and other additional information.

Research done by Jim Noel and Ron Curtis. Data entry done by Ron Curtis and Link Crawford. Web support given by Mark Fenbers.

To get updates on La Niña or El Niño, see the latest NWS/Climate Prediction Center Advisory.*