So the big question on the minds of many people over the past few days has been whether or not we will have a white Christmas? As we've alluded to before in Wausau, at least one inch of snow has been on the ground since 1931 on December 25th 93% of the time, while in Rhinelander it is a 96% likelihood. Of course, those times when it wasn't a winter wonderland for the holidays could be explained due to prior snow having melted or the weather pattern just being downright dry. To get started, here is the breakdown of the years of Christmas past for Wausau when less than an inch of snow was on the ground, thus being a Brown Christmas.
The most recent time which Wausau was without snow for Christmas Day was in 2002. This lead me to do some research to see how December 2011 has stacked up in comparison to that year. For starters, check out the difference in snow depth in the state for this year compared to '02. You'll notice that although there isn't a lot, about an inch or a bit more can be found in much of the Badger State this year, while in 2002, there was very little snow at all.
Temperatures and snowfall for these two Decembers can perhaps shed a bit of light on the dearth of snow. Back in 2002, there were 6 days of 40 degree highs, with 12 days when the mercury pushed into the 30s. This in the end worked out to an average temp of 23.7 degrees, which is 4.7 degrees above average. That might sound like a lot, but in reality it only ended up ranking as the 20th warmest December on record in Wausau. Fast forward to December 2011 (through the 23rd), and the temps in Wausau averaged out to 25 degrees, which is 6 degrees above average. So it has been warmer this December thus far, and if we stopped right at this point, it would go down as the 18th warmest for Wausau. Thus in the grand scheme of things, similar when it comes to the temperature listing in the record book.
As for snowfall, December 2002 featured just 2.3" of snow, the 6th least snowiest December. Through late afternoon on December 23rd of this year, Wausau had picked up 6.5", which doesn't even place in the top 25 for the least amount of snow. The two reasons Wausau doesn't have much snow on the ground to this point was due to some melting that took place due to mild conditions, plus a storm on December 14th-15th that produced over .40" of rain, washing away most the snow that had fallen on December 3rd & 4th.
Overall, will the winter of 2002-03 be a telltale sign of what we can anticipate for this winter season? Probably not. The similarities of this December and the one 9 years ago aside, the overall weather pattern was in a different mode. In 2002-03, a moderate El Nino (warmer waters in the western & central Pacific) was ongoing. This type of set up leads to somewhat milder temps & lower than average snowfall in our region. Compared to the last 10 years, it was the 3rd coolest at 16 degrees, which is 0.9 degrees below average. A bit surprising in the temperature department. The seasonal snowfall in 2002-03 of 46" was the 2nd lowest in the past 10 years, and about 14" below average in all. Obviously, we've got a way to go when it comes to this winter, but we are in a moderate La Nina pattern (cooler waters in the western & central Pacific), which tends to mean cooler & snowier conditions. December 2011 instead has been the opposite. However, there is more to the story for this first month of the winter season.
Let's start off with the jet stream, which drives storm systems across the country. Over the past couple of years in December, we have seen sizable snowfalls during this time, as storms formed over the southwest and central Rockies, pushing northeast and positioning North Central Wisconsin in the target zone for cold air & heavy snow. This month has featured a split northern & southern jet stream, which has cut off the moisture packed storms to the south. This also explains why the days leading up to Christmas, heavy snow made headlines from Arizona to Oklahoma (under the influence of the southern jet stream) and the Upper Midwest experienced passing clipper type systems which only managed to squeeze out at most an inch or two of snow.
The other players in the current weather pattern are the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). Since mid-November, both of these oscillations, which are factors in where the jet stream is aligned up across North America, have been in a positive phase. Don't believe me, below are the charts for each of them.
What does this all mean? A positive trend of both of these oscillations equates to milder & wetter conditions in the eastern part of the U.S., with the Upper Midwest being drier, along with milder temps. More so, the arctic air has stayed locked up to the north in the Arctic and parts of Alaska, at times shifting down into the northern and central parts of Canada.
With all of that said, it is a safe bet that eventually this winter, there will be at least one outbreak of sub-zero temperatures in our neck of the woods, and some snow storms. We may not see record snowfalls like we experienced at times in the past two years, but there will be notable amounts. It is hard to have a happy medium. No less the weather is always changing and for the winter weather enthusiasts, we are only in the early days of the winter season according to the calendar. On the flip side, it has managed to be cold enough for the ice fishers to get out on the frozen lakes. The moral of this story, stay tuned!
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