2015-2016 Winter Outlook, Explanation, and Local Information

The 2015-2016 Winter Outlook indicates that our upcoming winter has an increased chance of having above normal temperatures and equal chances of above or below normal precipitation (not necessarily snowfall).

One of the main drivers behind this outlook is the presense of an El Niño, which is expected to become one of the strongest on record (record keeping began in 1950). What is El Niño? Basically it's the warming of the sea surface across the equator in the Pacific Ocean such that above normal water temperatures are observed. An El Niño is considered strong when a section of the equitorial waters reach +1.5 degrees C above normal. Even though these waters are thousands of miles away, strong El Niños can have drastic impacts here in the Northern Plains and worldwide. This was well documented and observed during the last strong episode 17 years ago (1997-98). For more information on how El Niño affects our weather, check out this video: https://www.youtube.com/watch?v=_Tuou_QcgxI and for even more information, visit https://www.esrl.noaa.gov/psd/enso/.

Below is a graph of the 6 strongest El Niño years, along with 2015 so far. The x-axis displays time, depicted by 3 month averages (SON = September October November, OND = October November December, and so on).

A good place to start then, when predicting how the coming winter will turn out, is to look back at the winters from these past strong El Niño years. Below are temperature and snowfall departures from normal over the winter months (December, January, and February). Years are in order of strength.

1997-98

1982-83

1972-73

1965-66

1957-58

1991-92

Here's the average temperature departures for all 6 events across the US. Notice the High Plains typically benefits the most in terms of increased warmth during strong El Niño years.

A couple things to keep in mind:

1.) 6 El Niño episodes is a very small data set to work with - we must be cautious in inferring too much information.

2.) The temperature departures include and average out both high and low temperatures. Warmer low temperatures can have a big impact on the overall average.

3.) Even if we end up with above average temperatures (or even far above average) as a whole, there will still be bitter cold and snowy days. Only the frequency of these events should be reduced.

4.) Although we typically observe below average snowfall during these years, total precipitation is typically right around average. The difference is that more of it falls in the liquid form.

Finally, did you notice how two of the years featured widespread below average temperatures, and that one of the years recorded predominantly above average snowfall? This is a reminder that we can't put all our eggs in one basket - there are other climate factors to consider besides El Niño that have the potential to drastically impact our winter and derail the outlook.

One such example is the Arctic Oscillation (AO). In its negative phase, the polar low pressure system, better known as the Polar Vortex, is weaker which allows Arctic air to push further south. Think of it as a spinning top - the slower it spins the more it wobbles. In this case, the cold air "wobbles" futher south. The problem is, this is very difficult to predict and it can change on a weekly basis. For more information and some great graphics to help explain, visit: https://climate.ncsu.edu/climate/patterns/NAO.html.  Another example is the Pacific Decadal Oscillation (PDO). It's similar to the El Nino Southern Oscillation (ENSO, in which El Nino is the warm phase) in that it has cool and warm phases and shifts over time periods of years. Find out more here: https://climate.ncsu.edu/climate/patterns/PDO.html.