Winter is only a couple of months away. The first thing I’ll say is that Winter 2012-13 is nearly certain to be colder and snowier than last winter.
Second thing I’ll say is my usual disclaimer: A winter weather outlook should ALWAYS be taken with a grain of salt. You can not use it to plan a snowmobile vacation on Presidents’ Week. The best we can do is figure out how the present large scale atmospheric circulation patterns may affect the weather going into the winter.
Once a winter outlook has been issued, trends must be monitored closely. Last year, most meteorologists (including myself) were pretty bullish in October for a cold and snowy winter. Snow cover over Eurasia grew at a near record clip in November, which created further excitement. However, the deep and persistent dual positive phase of the Arctic Oscillation/North Atlantic Oscillation kept much of the United States warm and mild through most of the autumn into early December. This alerted me to the real possibility that Winter 2011-12 was going to be a dud and I altered my outlook accordingly. Many notable forecasters kept banging the drum for a dramatic turn around to a cold and snowy winter, despite the growing mountain of evidence to the contrary. If the data changes, your forecast must change!
My approach will be to determine what might happen the first couple months of winter, then tackle February and March when the time comes. So, let’s take a look at what’s going on.
North Atlantic Oscillation:
The Northern Atlantic Oscillation (NAO) has been mainly neutral or negative over the summer into the autumn. In the winter, the negative phase of NAO often manifests itself in a Greenland Block. This pattern can force Arctic air into the eastern United States. Last winter, we were locked into the positive phase of NAO which favors warmer weather over the eastern United States. If the negative trend continues into early winter, this would be a seismic change over what we had going into last winter. That would be a great thing. 🙂
Arctic Oscillation:
The Arctic Oscillation was been all over the map this summer into early autumn. Last year, we were locked into the positive phase of the Arctic Oscillation throughout autumn and into the winter. This resulted in a strong zonal (west to east) jet stream across Canada, which often kept Arctic air masses trapped way up north. Forecast models are indicating a trend toward the negative phase of the Arctic Oscillation over the next 1-2 weeks. If this pattern actually develops and holds into this winter, a relaxed jet stream would allow Arctic air masses to spill into the United States more often. That would be another good thing. 🙂
Check out how the Arctic Oscillation works.
Record low September Ice Cap:
The polar ice cap shrinks in the summer and grows back in the winter. This September witnessed the least expanse of polar ice on record. Oddly, that may help us this winter. As ice melts, the darker water absorbs more heat from the sun. This in turn accelerates the warmup over the Arctic region during the summer and decreases the temperature gradient between the Equator and North Pole. A weaker temperature contrast results in a weaker jet stream. As summer transitions to winter, the weaker jet stream easily buckles under the weight of the building cold in the Arctic. The previous record for smallest September polar ice cap occurred in 2007. The follow up winter of 2007-08 was very robust for snow in the Adirondacks. There may be a connection between low September ice and the negative phase of the Arctic Oscillation, another check mark in our favor. 🙂
El Niño/Southern Oscillation:
A strong El Niño can really screw up winter around here. We have been in a neutral/weak El Niño phase of the Southern Oscillation since this summer. That’s just a fancy way of saying the Pacific equatorial waters are slightly warmer than normal in the east and slightly cooler than normal in the west. Assuming that El Niño remains weak or neutral, it won’t be much of a factor this winter.
Northern Hemisphere Snow Cover:
The North Hemisphere snow cover is off to a good start over Siberia, the ultimate winter cold air source. If there is a rapid expanse of snow cover over Eurasia and Canada into November, that could be a harbinger of good things to come in December for us. 🙂
Warm Western Atlantic Waters:
The waters offshore from the northeastern United States are unusually warm. I can’t find a recent occurrence of an anomaly THAT strong! This additional heat energy may add serious punch to coastal nor’easter storms this winter.
Preliminary Outlook for November, December and January:
The weather circulation patterns heading into winter appear favorable, but the Arctic will need some time to recover from the near record warmth it experienced over the summer. Hence, I think that November may end up somewhat warmer than normal with lackluster snowfall around here. December and January may be robust for snow with near normal temperatures. Of course, there may be a thaw or two thrown in. I don’t foresee a wicked cold start to the winter, but you only need to be “cold enough” for snow. Once we transition into winter you can check my weather blog and daily forecasts for the latest information.
Drop a comment and let me know what you think.
