An ENSO event is defined as period of five consecutive 3-month periods where the waters of the Pacific along the equator are either +0.5 degrees C warmer or -0.5 degrees C cooler-than-average. The warmer conditions are designated as an El Niño, while the cooler-than-normal state is called a La Niña. As indicated by the current sea-surface temperatures (Figure 1), a weak La Niña is present, and is expected to continue through the spring.
Figure 1. Current sea surface temperatures (SST) from the Climate Prediction Center.
The latest weekly Niño-3.4 index value was -0.8 degrees Celsius, and the Niño-3 and Niño-1+2 indices were at or below -1.0 degrees C during much of January. Based on the latest observations and forecast guidance, forecasters believe this weak-to-moderate La Niña (3-month Niño-3.4 values between -0.5°C and -1.5°C) is currently peaking and will eventually weaken into the spring (Figure 2).
Figure 2. ENSO Forecasts (Climate Prediction Center)
Based on previous events, a La Niña is typically strongly associated with a drier-than-normal weather pattern.
Figure 3. Frequency and strength of precipitation anomalies during La Niña events (Climate Prediction Center)
For Kansas, of the 15 La Niña events noted, only two events had a positive (above-normal) precipitation anomaly during the spring season of February through April. During the 2000 event, the February to April departure from the 1981-2010 normal was 2.41 inches, while the average deficit is -0.99 inches (figure 4).
Figure 4. Precipitation departures from normal during La Niña events for Kansas. Weather Data Library
This pattern of a negative anomaly is one of the factors guiding the Climate Prediction Center’s outlook for the period shown in Figure 5.
Figure 5. Three-month precipitation outlook (Climate Prediction Center)
As seen in the normal precipitation maps below, March and April are critical months for moisture. A dry pattern at this time will likely result in intensification of the current drought conditions.
Figure 6. Normal precipitation in Kansas for March (upper) and April (lower) from 30 years of data.
Mary Knapp, Weather Data Library
mknapp@ksu.edu
Xiaomao Lin, State Climatologist
xlin@ksu.edu
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