Currently the Pacific Ocean is in what is known as an El Niño. El Niño is a natural climate phenomenon marked by warmer-than-average sea surface temperatures in the central and eastern Pacific Ocean near the equator.
Since 1950, there have been approximately 20 El Niño events. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, a positive or negative ONI (Oceanic Niño Index) of 0.5 degrees C must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons. On the other hand, the Climate Prediction Center (CPC) considers El Niño or La Niña conditions to occur when the monthly Niño3.4 OISST departures meet or exceed +/- 0.5 degrees C along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months. By either standard, we are currently in a moderate El Niño.
Figure 1. El Nino diagram (from NOAA)
These episodes share several common attributes, including a tendency to emerge in late spring and grow in intensity through the following fall, with a typical life span of 9-12 months. The presence of El Niño can significantly influence ocean conditions and weather patterns across large portions of the globe for an extended period of time.
A typical El Niño episode affects U.S. weather patterns by shifting the Pacific jet stream - thereby altering the movement of air masses and the tracks of cyclones that determine temperature and precipitation patterns. El Niño affects U.S. temperature and precipitation throughout its life cycle, though the more widespread disruptions occur in the cold season.
On average, during the cold seasons, El Niño is associated with above-average precipitation along the Gulf of Alaska coastal region, across the Southwest and the Gulf of Mexico coastal region, while drier conditions prevail across Hawaii, the Pacific Northwest, and over the Ohio and Tennessee Valley. Temperatures are typically above-average across Alaska and the northern U.S., and cooler along the Gulf of Mexico coastal region. El Niño suppresses hurricane activity in the Atlantic. It also affects central-eastern Pacific tropical storms, with a tendency for storms to recurve farther north and east into Mexico and the southwest, this can enhance the monsoon moisture in the Desert Southwest and into Kansas.
The Climate Prediction Center has a tool that compares a composite of the ENSO events to average conditions. Below are pairs of precipitation impacts over various seasons. The first map of the pair shows the anomalies, while the second shows the frequency of occurrence:
The most recent ONI value, which covers the April-June 3-month period, is 0.9 degrees C. This is considered a moderate event. The forecast is for this event to persist through the winter. The anomalies illustrated above show that Kansas tends to have wetter-than-average conditions during the autumn and late winter periods. A table of average Kansas precipitation versus selected El Niño events shows that tendency:
The 1987-88 El Niño event is a good analog year in that the strength of the episode during the April-June (AMJ) period is similar to 2015, and the event persisted through the winter. Note that there was a dry anomaly for the Aug-Oct (ASO), Sep-Nov (SON) and Oct-Dec (OND) periods. When comparing the ASO composite map, it is evident that the Southeastern Division has a dry pattern during this time-frame. Since this region has higher average precipitation, a dry period there will skew the state average to negative values.
Here are the Climate Prediction Center’s outlooks for the ASO 2015 and FMA 2016:
A wet August-September would be favorable for establishment of the winter wheat, but could create problems with harvest for summer row crops. A wet pattern during the February-March period could keep the soil moisture profile saturated but is likely to create problems with spring field work.
Mary Knapp, Weather Data Library
mknapp@ksu.edu
Chip Redmond, Weather Data Library
christopherredmond@ksu.edu
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