Long-range Weather Forecasting

Wondering what lies ahead in terms of winter weather? Find out how meteorologist get their extended forecasts.

| January/February 2018

Everyone wants to know whether they will have to deal with harsh winter conditions, and they like to know as soon as possible. This takes us into the realm of “long-range weather forecasting” and its most famous product, the “winter outlook.”

Although numerous people and groups put out winter forecasts, the official forecast comes from the National Weather Service’s (NWS) Climate Prediction Center. The meteorologists there produce long-range monthly and seasonal forecasts up to a year in advance, and these are updated every month. So, you can get a forecast for next winter by the end of the current winter. As you approach the time period in question, forecast confidence typically increases.

I should mention here that the NWS uses the terms “forecast” and “outlook” for different situations. Forecasts are more precise with specific temperature and precipitation probabilities given, but only go out to seven days. Beyond this time frame, the NWS uses the term “outlook,” and predictions are less precise — typically just comparisons to normal or average conditions.

For extended outlooks, like the one for the following winter, temperature and precipitation predictions are given as above or below normal, or as “equal chances” (of above or below normal). This can be inferred as normal or average since there are no strong indications of abnormal conditions. The final forecast for the coming winter is issued in mid-November.

Making predictions

So how do NWS meteorologists make long-range forecasts, especially the winter outlook? They use computer models. When forecasting out to 14 days, there are mathematical models that will actually depict weather systems that control our weather. But the errors with these mathematical models compound over time, and they are fairly useless after 14 days. Beyond that, meteorologists must rely on less accurate statistical models. They will look at past conditions and consider persistence and any noticeable trends.

With nearly 70 percent of the Earth’s surface covered by water, ocean temperatures are a major factor. If possible, they look for large-scale weather patterns — patterns that are capable of lasting for months and can control the weather. To a large extent, the winter outlook is based on the El Niño/La Niña (EN/LN) cycle. The media has often made mention of them in recent years, and meteorologists first expressed interest in them back in the 1980s. The reality is that this cycle has been going on for hundreds, maybe thousands of years, and we’ve only just realized it.

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