It’s that time of year again. Winter people start emerging from their summer hibernation caves and tune up their skis, boards, sleds, and snowshoes for an anticipated winter of epic snowfall. The last few years have been a roller coaster for snowfall across the US with a record setting 2010-2011 winter followed by a disappointing 2011-2012 season. Fortunately things are looking up for many parts of the US as early fall models are pointing towards below average temperatures and average to above average snowfall in many areas.
First let’s take a look at winter 2012-2013 and see where we’ve come since then. We talked a lot about the NAO (North Atlantic Oscillation) in last year’s forecast because that is what so negatively affected the east coast area in winter 2011-2012. Typically a negative NAO will result in a cold snowy winter for the east and a positive NAO will result in a warm dry winter for the east. The figure below shows the NAO phase for winter 2012-2013 in the shaded area. Needless to say the NAO was negative and actual snow conditions were substantially better than the year prior. This is in line with what we predicted in last year’s forecast.
Last year’s forecast models were trending towards a weak El Nino winter that would have brought good snow for the Colorado, Utah, and Wyoming areas with below average snow for the northwest and into Montana. This isn’t what happened. Although an El Nino started to form in late summer 2012 it stalled out in late fall and ended up in neutral conditions. With a neutral El Nino, or “La Nada” as some call it, in place the normal weather drivers took over and brought pretty average winter conditions for those areas. Although it was average, it was a big improvement over the previous winter.
Now let’s take a look at the current conditions and compare them to the last three winters that consist of one record setting above average snow year, one record setting below average winter, and one very average snowfall winter. The NAO spent the majority of last summer in positive territory as seen in the shaded area of the plot below showing through September.
As you can see it’s now trending downward and the latest models are suggesting this trend will continue. Bottom line I expect it will remain positive through the fall and possibly early winter. But more than likely it will be in negative territory for most of the winter.
The summer of 2012 had a strong negative NAO which stayed negative for most of winter 2012-2013 so that is not real analogous to what we see for this coming winter or even the record mild winter of 2011-2012, where the NAO started negative in the summer and sharply went positive for the winter, and the epic winter of 2010-2011 that was just a more extreme example of last winter. This year really is a whole new deck of cards unlike the last three in regards to the NAO. The most recent year that was similar to what I expect this winter was winter 2007-2008 where snowfall was above normal in the north east with some local all-time-record snow totals for Concord New Hampshire and Burlington Vermont.
The next big player to look at is the state of the El Nino – La Nina cycle (ENSO). Last year I predicted a weak El Nino. Turns out I was wrong and the El Nino cycle stayed about neutral. The plot below shows the forecast for several ENSO (El Nino Southern Oscillation) models of how much the sea surface temperature will vary in degrees Celsius from normal this winter in the shaded area. Usually I look at the average between all of the models to get a scope of what might actually happen. This year it isn’t really necessary. For conditions to be in any kind of El Nino or La Nina phase the sea sufferance temperature (SST) variance from normal, AKA Anomalies, would have to be outside the area marked by the red lines.
None of the models come close to going outside the ‘neutral’ El Nino zone in the winter months to come.
Looking at past years with similar conditions for the west I expect slightly below average temperatures for Montana, Wyoming, western Colorado, and eastern Utah with average to slightly above average temperatures for WA, OR, ID, CA, NV, and AZ. El Nino and La Nina events tend to swing the pendulum one way or the other for snowfall; splitting the southwest and northwest with one having great snow and leaving the other in a drought. In the absence of an El Nino, history has shown, we’re likely to get a much more even distribution of average to above average snowfall all over the western US including the Wasatch, front range, Cascades etc. Although it’s still early to tell for sure, I see no indication that it will be anything but a snowy winter for the west.
The ENSO (El Nino Southern Oscillation) is such a big force in weather that when an El Nino or La Nina is present it pretty much defines the winter weather for the western half of the US. In a year like this where the ENSO will be neutral opens up the possibilities for many other driving forces to move in and make winter interesting. As a generalization I would expect average conditions for snowfall and temperatures for most of the west. With the official start of winter still being almost 3 months away and with so many possible localized variables in the absence of an ENSO event your local area could be in for anything this winter.
Now for all of you that just want the overall bottom line. The northeast should expect very cold temperatures with lots of snow and frequent storms. Keep caution out for some bad ice storms in the southeast. Montana, Wyoming, western Colorado, and eastern Utah will have a very cold winter with above average snowfall while WA, OR, ID, CA, NV, and AZ will have about average temperatures and average snowfall with the possibility for well above average snowfall in localized situations. As usual I have posted a map of this year’s Farmer’s Almanac winter forecast since it’s always a good idea to consider more than one point of view when making your winter plans.