It’s beginning to look like the winter of 2017-2018 may be a La Niña winter. Forecasters said in late September that there is about a 55% to 60% chance that a La Niña will develop from the current ENSO-neutral (El Niño Southern Oscillation) conditions that have prevailed since February, and they issued an official La Niña Watch.
For Kansas, that isn’t exactly a promising outlook. While El Niño conditions often bring much-needed moisture to Kanas during the winter and early spring, La Niña tends to be the opposite — a warmer and drier winter and early spring — and depending on the strength of the event, a hot, dry summer.
A weak, short La Niña occurred last winter, while neutral conditions were recorded the year before. Both 2016 and 2017 brought warm, dry winters, followed by wetter, cooler springs as La Niña faded.
The last strong La Niña was in the winter of 2010-2011 and 2011-2012. Kansas residents have not-so-fond memories of the summers that followed, which brought some of the worst blistering heat and drought in Kansas history.
La Niña conditions have also been tied to a more active tornado season than ENSO-neutral or El Niño events.
If any good news can be attached to the forecast, it is that it’s very uncertain what is about to unfold in the equatorial Pacific. It could be La Niña. It could be La Nada (as the Jet Propulsion Laboratories’ top ENSO scientist, Bill Patzert, likes to call “neutral.” It could even push toward a weak El Niño.
An ENSO watch has become a bit of a fad in the 40 years or so since it first became the subject of a lot of scientific notice, but the reality is that not a lot of evidence about it has been examined, and the global effects of the cycle are not reliably predictable.
For example, the very strong El Niño of 1996 brought endless rains, overflowing reservoirs and mudslides to southern California. When similar conditions developed in 2015-2016, southern California braced for a repeat of those conditions. But they didn’t happen. Why not?
For one thing, there was a pool of warm water that scientists called, somewhat unscientifically, the “warm blob” off the coast of California. Southern California, which was braced for torrential rains, didn’t get them. It did get a bit wetter-than-normal season, but not what forecasters had expected.
This year, there could be a number of variables in the ENSO forecast and how it impacts Kansas.
So exactly what is ENSO and why does it matter?
The El Niño Southern Oscillation is a recurring weather event in the equatorial Pacific Ocean. During an El Niño, strong easterly trade winds push warm waters to the east and cause warmer waters to pile up. The increase in surface water temperatures has an impact on trade winds and atmospheric conditions.
During La Niña, the surface waters of the equatorial Pacific Ocean cool. The resulting change in wind patterns affects the course of storm systems around the world, including across North America, where rainfall and temperature patterns are impacted.
The change in storm track means that fewer thunderstorms pass over the Southern Plains during storm season, and that means that less rain falls.