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Snow or no? Greg's winter weather outlook

Asked to come up with a weather outlook for the coming winter, I hesitated, because I know that long-term forecasts are rarely helpful to people planning for their day-to-day life.

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Greg Fishel

Asked to come up with a weather outlook for the coming winter, I hesitated, because I know that long-term forecasts are rarely helpful to people planning for their day-to-day life.

There are so many examples from the past of where extremes – of cold and heat or snow and clear skies – balance each other out so that the forecast holds.

What is a "normal" Triangle winter?

October and November tend to be the driest months of the year in central North Carolina, so when climatological winter starts on Dec. 1, we're usually in a dry pattern.

The normal winter daily high temperature never averages less than the upper 40s.

The normal winter daily low never averages below the upper 20s.

That temperature range is the norm for the core of winter, but we've had days that don't get above freezing and days that are in the 70s. The average is an average of extremes.

And remember that, although it's rare, winter in the Triangle can last into March. In 1960, the coldest March on record for our area, snow was on the ground for at least half of the month!

This year is a La Niña. What does that mean?

This year, we are under La Niña conditions, which tend to favor mild and drier weather in the southeast.

Our weather stems from the jet stream over the Pacific Ocean, and in La Niña strong winds stir cold water from the depths of the ocean to the surface near the equator. This year, the jet stream, and those colder waters, will be far to the north of the equator, and cold weather won't make it as far south.

In a La Niña year, the weather in North Carolina tends to be milder and drier than normal.

Every once in a while, the jet stream can buckle and bring a surge of cold air to North Carolina. That's where the exceptions to a the average come in.

And it's hard to say that La Niña assures little or no snow. Since 1950, there have been 25 La Niña winters. In a third of those years, the Triangle had less than an inch of snow for the whole winter. In a third, we had 1 to 6 inches of snow; and in a third we had over half a foot.

Remember that the seasonal forecast is an average. In 2000, another La Niña year, Raleigh saw its greatest snowfall on record – 20 inches in a single January day.

December and January in that year were a little below normal. February was a little above normal but, even with that single big snowstorm, it averaged out to be a "normal winter."

There are so many examples from the past of anomalies that stick in the memory during an otherwise "normal" winter. In 1989-90, Greenville had 8 inches of snow on the ground around Christmas; Wilmington had a foot and a

half. It was the coldest December on record, and it was supposed to be a mild winter.

Then someone flipped the switch on New Year's Day. January and February 1990 were two of the warmest months ever, and the winter overall ended up being above normal. The forecast held.

But did anyone who heard that forecast expect such a brutally cold December?

Snow hat

Why is the Old Farmers' Almanac so accurate?

Any long-term forecast and trend can be generally accurate across the general pattern of a full season, but the devil is in the details.

In 1985, the long-term outlook called for a La Niña winter, but we saw the coldest weather ever recorded in North Carolina. Mt. Mitchell registered 34 degrees below zero. Raleigh had a day when temperatures dipped to 9-below. Ask those who lived through that winter and they'll remember that bitter cold, not the fact that overall temperatures averaged a bit higher than normal.

For those who plan on a seasonal basis – utilities looking to boost available heat or cooling power, farmers planning to plant or harvest crops – a seasonal outlook is enough.

The general public has such a great interest in weather that they want to know what to expect.

Snow photo

So what can we expect in winter 2017-18?

The coming winter overall will likely end up warmer and drier than normal, but that does not preclude the possibility of some anomalous or unusual things happening sometime within that 90-day period. All it takes is one and you've had a hellacious season.

It's been a bit dry, but we're not that far into the drier-than-normal range. We're near the boundary between normal and drier, so that adds a layer of uncertainty.

So while it's reasonable to expect the coming winter to be on the dry and mild side, that be any use to you in day-to-day planning? Not a whit.

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