El Niño Likely to Occur and What it Means For The Winter of 2018-2019 (Credit: NWS Climate Prediction Center)

Typical North American wintertime pattern during an El Nino winter (photo from NOAA).

​The National Weather Service Climate Prediction Center (CPC) and International Research Institute (IRI) are forecasting a 70-75 % chance of El Niño formation to occur over the next couple of months. All current conditions and forecast models are on a trend to favor the formation of a weak to moderate El Niño phase. It has only been a year or so since the last El Niño phase that ended in 2016. It was the strongest El Niño phase since 1997-1998, lasting for two consecutive winters in the years of 2014-2016. La Niña, the opposite of El Niño, defined by below average sea surface temperatures, persisted for only a single winter from 2017-2018 before conditions in the equatorial Pacific started to again favor development of an El Niño this coming winter. El Niño is part of an irregularly periodic variation in winds and sea surface temperatures over the equatorial region in the eastern Pacific Ocean, called ENSO (El Niño Southern Oscillation). This tends to be erratic when it comes to seasonal phases with El Niño occuring every two to seven years. Although predicted to be weak, this phase will certainly bring varying weather patterns to the United States this winter.

Between September 2017 and March 2018, sea surface temperatures (SST’s) in the central and eastern equatorial Pacific Ocean were below normal. Beginning in June of this year, these temperatures have started to increase, causing more positive SST anomalies. In September, the SST conditions climbed into an El Niño neutral phase. This means that neither El Niño or La Niña were present and that the climatic patterns over the equatorial Pacific ocean are near average. Since the past month of October, SST anomalies continued to increase, rising out of an El Niño neutral phase and into El Niño positive, meaning above average. In turn, due to the increase in SST anomalies, low level westerly wind anomalies where wind speeds and direction deviate from the average, are present with the strongest anomalies occurring over the Eastern Pacific. According to this recent observation of data, including model runs by the IRI and CPC, the development of weak to moderate El Niño within the next couple of months is highly likely.

Our ocean SST’s are a large influence on climatic weather conditions for the United States. When El Niño forms, The SST’s are above normal in the central and eastern equatorial Pacific off the coast of Peru. Higher SST’s directly influence our weather by increasing air temperature and moisture flux on the surface. Warmer air is able to hold more moisture.This allows it to efficiently collect water vapor that evaporates off the ocean surface. Predominant eastern flowing winds called easterlies, flow over the Pacific picking up moisture and driving it west to east over the United States. More water vapor in the air can increase the amount of moisture that gets driven into the United States by the easterlies. Therefore, this increases the potential of precipitation in certain areas. With this change in moisture content and increased surface temperatures, the United States may see changes in average temperature and precipitation, depending on location.

With this years winter weather outlook, predicted by the National Oceanic and Atmospheric Association (NOAA) there is a probability of seeing above average temperatures for the Western, Northeastern and central plains of the United States. Above average precipitation is expected in the southern United States while below average precipitation is expected in the Great Lakes region, northern Idaho, Montana and Dakotas area. Whether these seasonal outlooks will pan out, we have an idea of what to expect for this coming winter with El Niño in effect. It is important to know that long range forecasts like winter weather outlooks are merely an estimation of what the winter will look like. It is good to keep up with day to day forecasts in your area for the best updates on winter weather as we move through season.

 © Meteorologist Alex Maynard

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