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NIU’s Sebenste: ‘Get the snowblower ready’

October 23, 2014


NOAA winter weather outlook map

Recently, the National Oceanic and Atmospheric Administration (NOAA) released its winter forecast. Until mid-October, NOAA stated it could not accurately predict what sort of winter is in store for this region. That changed to a somewhat higher probability of higher-than-average temperatures for the northern plains and western United States and drier-than-average conditions for this area. This clashed with many private forecasts, including mine, which predicts a significant probability of a colder- and snowier-than-average winter.

So, which forecast is going to be right and why?

First, forecasting whether a winter will be colder or warmer than average does not carry a very high amount of accuracy yet. The best anyone can do right now is state that they believe that there is a higher or lower than average chance of a season being colder or warmer or wetter or drier than 30-year averages. From a scientific standpoint, we cannot make day-specific, or even week-specific, forecasts.

The Farmer’s Almanac tries to do that, but I believe its forecast is for entertainment purposes only. Remember, it called for a warm and dry winter here last year! Because its methodology is undisclosed, there is no way of knowing how the forecast was developed.

Even if we knew everything about our atmosphere, we could only forecast the weather with good accuracy out to three weeks. That’s because of what we call the “butterfly effect.” Even a butterfly, unpredictable in its stirring of the air, will cause wind currents and patterns downstream of it to change. But because we don’t know everything about our atmosphere’s current state—far from it—our accuracy is confined to about 10 days at best for a general forecast, and specific forecasts only to about three or four days. Therefore, it’s safe to dismiss the Farmer’s Almanac specific forecasts as just fun-to-read entertainment.

NOAA, however, uses two general conceptual models to forecast what the winter will be like: statistical and dynamic.

Dynamic models are something like computer model forecasts used to help predict the weather out to 10 days. These models use the current state of the atmosphere but provide only very general forecasts out to a year or so. Then, NOAA uses statistical models to look at recent past data to figure out if there’s a pattern developing. The dynamic models are assuming an El Niño, which means higher-than-average temperatures in the east-central Pacific Ocean this winter, providing a higher probability of a warmer-than-average winter. Next, looking at the last 20 years or so, most of the winters have been milder than the long-term average. Given this, the NOAA forecast puts higher probabilities toward a warmer-than-average winter for parts of the northern United States and a no-confidence forecast for temperatures for us with a higher confidence of a drier-than-average winter.

My forecast takes into account the same models that NOAA does, in addition to analogs. The analog method involves examining a forecast scenario and comparing it to a day in the past when the weather scenario looked very similar (an analog) and predicting that the weather will behave the same as it did in the past.

First, an extensive buildup of snow cover in October in Siberia, Asia and North America is one of the prerequisites for a cold winter in North America. But it’s not the only one. You also need warmer-than-average water in the northern Pacific and Gulf of Alaska to consistently push the jet stream north into Siberia, which then forces it southward downstream into the Midwest. As of October, the water temperatures are some of the warmest we’ve ever recorded in this area of the Pacific.

Finally, there can’t be a strong El Niño in place. This is where I think NOAA is going wrong; the models have forecasted our region to be in an El Niño, and it has failed to happen. Those models still assume that we will be in one this winter, despite the sub-surface water observations now suggesting it is less likely to happen. That causes a wrong bias, I believe, in NOAA’s models.

When looking at these three factors – warm water in the north Pacific, extensive and early snowfall cover in the northern Hemisphere and Siberia and the lack of a strong El Niño –  I ask the question if this has happened before in the late autumn, and if so, what happened in the following winter.

The answer is that it isn’t pretty. There have been 12 times, or analogs, where this setup has occurred, and out of those 12 winters and late autumn setups similar to this one, every single one produced a colder-than-average winter.

These aren’t the only factors that determine our winter weather; there are considerably more. However, these three are important in determining the overall patterns that will play out over the next five to six months. Barring a surprise El Niño, and because there is a significant and direct correlation between these factors and a bad winter, get the snowblower ready for another tough winter.

Gilbert Sebenste

Gilbert Sebenste

Gilbert Sebenste is the staff meteorologist at Northern Illinois University. NIU weather resources may be found on the NIU weather page,