The current El Niño is fading, and a La Niña watch has been issued. The most recent ONI (Oceanic Niño Index) for the February, March, April (FMA) period is +1.6 degrees Celsius. However, the weekly update from May 11th shows a significant decrease in the anomalies across the equatorial Pacific. The outlook favors a move to neutral conditions during the summer, with a 75 percent chance of a La Niña by autumn.
A La Niña event typically brings warmer and drier-than-normal conditions to the Plains during the late summer and early fall. The first map shows the normal precipitation in Kansas for the August to October period, while the second shows the August to September precipitation anomalies during La Niña events.
This pattern of a negative anomaly is one of the factors guiding the Climate Prediction Center’s outlook for the period, as seen below.
The Climate Prediction Center’s long-lead outlooks have the greatest skill when the ENSO is strongly in one phase or another. The outlooks are least reliable when the ENSO is in the neutral phase, as other global circulation features battle for dominance. Historically, summer is a neutral period and serves as the transition between either Nino/Nina or vice versa. However, as summer ends, the probability of a dominant pattern (Nino/Nina) increases as shown below, justifying the CPC’s outlooks for this coming late summer and fall.
Mary Knapp
mknapp@ksu.edu
Christopher Redmond
christopherredmond@ksu.edu