The National Weather Service Climate Prediction Center is now predicting that the end of 2018 and the first months of 2019 will see at least a mild El Niño. The forecast says there is a 70% to 75% chance that an El Niño will develop.
That in turn means a forecast for a warmer-than-normal winter across the U.S., with the 90-day outlook for Kansas showing a 40% probability of a warmer-than-normal winter and equal chances of above- or below-normal precipitation for the period.
"Normal" for temperatures and precipitation for calculation purposes is arrived at by averaging reported temperatures and rainfall or snowfall over the past 30 years. For the past several years, winters have been warm in most of Kansas and have also tended to be very dry.
The same precipitation forecast is true for most of the middle United States and comes as a rainy end of summer and early fall erased the pervasive and extreme drought conditions that affected central and eastern Kansas over much of the growing season. Drought has also been eliminated in northern Missouri but still remains extreme in Utah and Colorado. The El Niño forecast predicts that the drought in the western states will also be mitigated over the next 90 days.
What is El Niño?
According to the National Weather Service Climate Prediction Center, El Niño is a seasonal event that occurs in two-to-seven-year cycles. It is characterized by warmer-than-normal surface waters in the central and eastern tropical Pacific Ocean, and it is closely associated with a global atmospheric oscillation known as the Southern Oscillation.
During an El Niño, lower-than-normal air pressure is observed over the eastern tropical Pacific, and higher-than-normal pressure is found over Indonesia and northern Australia. It is the change in pressure that causes weaker-than-normal east-to-west winds.
As the warm episode develops, the normal rainfall and atmospheric circulation are affected. The equatorial central and eastern Pacific tend to see more rainfall while Indonesia, Malaysia and northern Australia see reduced rainfall and even drought.
EL NIÑO EXPECTED: The National Weather Service Climate Prediction Center says an El Niño episode in the winter of 2018-2019 is probable. For Kansas, that will mean a warmer than normal winter, the center says.
The disruption in atmospheric patterns can cause weather anomalies around the globe. During an El Niño winter, mid-latitude low pressure systems tend to be stronger in the eastern North Pacific, pumping abnormally warm air into western Canada, Alaska and the extreme northern portion of the U.S. Storms also tend to be stronger in the Gulf of Mexico and along the southeast coast of the U.S., which has resulted in wetter weather in that region
The Climate Prediction Center updates its ENSO (El Niño-Southern Oscillation) forecast every month, issuing a new forecast for the coming 90 days.
The opposite of an El Niño is a cooling of waters in the same areas of the Pacific Ocean, called a La Niña. Episodes of heating and cooling of the ocean waters tend to last from 9 months to a year but can persist for three or more consecutive years.
El Niño and La Niña episodes don’t always follow each other immediately. Often, as has been the case of the past several months, the conditions are described as "ENSO neutral."