A first look at winter

A real autumn air mass will roll into our region this weekend, and at some point Saturday or Sunday, you'll think about winter.

Hopefully, you won't think too much about winter, because we have a lot of beautiful fall weather ahead before the next season change.

But if the thought crosses your mind about winter 2011-12, here's the answer ... it looks like a mixed bag again this year, much like last winter. And some meteorologists say our upcoming winter could more closely resemble 2008-09, which was among the craziest winters we've experienced in a long time.

First, a review of last winter -- 2 1/2 months of nasty, cold and sometimes wet weather; followed by one month of an early spring.

The same players are here again this year. La Nina has reappeared, after disappearing late in the spring. La Nina is a condition of colder-than-average waters in the eastern Pacific, and it usually translates into dry, mild weather for the southern tier of the United States. It also was blamed in part for the tornado outbreak last spring, but let's focus on winter for now.

If La Nina were the only condition of importance, we'd be looking for a dry and mild winter.

But another key factor, as we learned last year, is the North Atlantic Oscillation, or NAO. That condition describes the overall path of the jet stream in the upper ranges of the Northern Hemisphere. When the NAO is negative, as it was for the first two-thirds of last winter, it means cold air masses and occasional storm systems dive from the arctic into the eastern United States (and also into Great Britain and northern Europe, on the other end of the stream).

Last December and January were very cold months, and there were notable winter storms on Christmas Day and again Jan. 9-10. We had a few other close calls on winter storms, and the Mid-Atlantic got hammered.

Then, like someone flicked a switch, the NAO relaxed around Valentine's Day. La Nina took stronger control, and high pressure built over Texas. We had warm weather and mostly dry conditions from mid-February into much of March.

But what about the winter of 2008-09, which some meteorologists expect in some form this winter? It was wild. Overall, temperatures were around average for the season (see map at upper right). But try these extremes:

-- December was mild. It reached 67 degrees on Christmas.

-- January and February featured wild swings. It dropped to 9 degrees on Jan. 17 but hit 60 or higher six days. Feb. 5's low was 13, but it climbed to 71 degrees just two days later.

-- Then came March. A strong winter storm struck on the 1st. After dumping nearly 2 inches of rain and causing flooding, the precipitation changed to snow that Sunday evening, and we got 4 inches in Charlotte (the only measurable snow of the winter). A foot fell near Shelby. Then, less than a week later, it was 80 degrees. In fact, we had six days of 70 or warmer in the first part of the month.

We'll fine-tune the forecast in weeks to come, but this will give you something to think about as you break out the sweaters and jackets this weekend.