Sven explains Winter Outlook predictions

Minnesotans are always interested in long range Winter outlooks, but how are they compiled, and are they accurate? Sven Sundgaard explains.

GOLDEN VALLEY, Minn. - Everyone always wants to know about the long-term outlook for whatever season ahead, especially winter in these parts. NOAA created its annual buzz by issuing its official winter forecast for the country Thursday.

The question is, how accurate are these forecasts? KARE 11 Meteorologist Sven Sundgaard broke it down for us Friday on Sunrise.

First off, climate forecasts are a sketchy business. We all know how drastically the weather can change 7 days out, let alone 90 or 120 days. NOAA Climate Scientists attempt to examine which large scale patterns on the globe may influence the patterns more or less. It is important to note these forecasts are probabilistic forecasts, and are NOT black and white (or I should say: warm/cold). For example, last winter NOAA was predicting a greater chance of a colder than normal winter, than a warmer than normal winter. That means, it appeared more scenarios played out that yielded a cold winter than a warmer one. What happened? Well, we all may recall it was one of the warmest winters in recent years: tying nearly the previous winter of 2015-2016, which was an (expectedly) mild El Nino winter.

A player in last winter’s warmer pattern was La Nina, albeit a weak one. This year La Nina is once again forecast to be a player. When we look at the winter seasons since 1980, 10 have been El Nino winters, and 11 have been La Nina winters. Of those, the strongest predictor for Minnesota is El Nino. 70% of the time an El Nino yields a mild winter for us, but that still means 30% are colder, which isn’t something to completely ignore. La Nina is much less definitive around here: of those seasons only 55% were cooler than normal compared to 45% of La Nina winters that were milder, so there’s only a slight correlation corresponding to cooler conditions.

What are El Nino/La Nina? They are the patterns that develop in the surface water temperatures off the equatorial west coast of South America. El Nino is when the trade winds at the equator weaken and warm water builds off the coasts of Peru and Ecuador. La Nina is the opposite, when trade winds increase and push the warmer waters west to the western Pacific, causing upwelling...  which means colder than normal waters off the coast of South America. This year a weak La Nina looks to develop, but in terms of forecasting a winter pattern there can be many other influences, and in the background of all these phenomena is global climate change. Our planet is getting warmer and so is Minnesota. There are still ups and downs (like the 2013-2014 winter which was very cold) but overall the trend is warmer. Combining all those factors I would bet on a normal or slightly warmer than normal winter, but probably not as mild as the last two.

The official NOAA forecast is for ‘equal chances’ of a colder or warmer winter, but a much stronger indication that our chances could be higher of a ‘wetter than normal’ winter, which for us means possibly more snow (or rain). Either way, we’ll ALL know soon enough! Enjoy the mild October temps in the meantime.

© 2017 KARE-TV


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