Supposedly, this is the season that La Nina would deliver tons of snow, especially across the western U.S. and northern New England. Thankfully, the first part of the season did not disappoint, though the storm patterns weren’t always typical of La Nina.
First, let’s dive into some of the data. Thankfully, sites like bestsnow.net and SNOTEL have done the hard work of compiling the snowfall statistics. Through the end of 2010, the snowfall in most locations is well above average for this time of year (see graphic).
While La Nina is alive and well in the equatorial Pacific Ocean (in the form of below-average water temperatures), we only saw the typical La Nina storm track in November and early December. During that time, storms moved into the Pacific northwest and eased down through Wyoming and Colorado. This ensured that the most snow fell in the northern half of the U.S., which is typical of La Nina.
However, the last half of December featured a weather pattern that was more typical of El Nino with a strong storm track from the southwest. During one week, Mammoth Mountain in south-central California recorded a storm total of more than 200 inches at its summit, while other areas in southwestern and central Colorado saw 50-90 inches.
So what’s the deal with the storm track, and why isn’t it behaving? Good question, and I wish the answer was clear cut. One explanation is that the weather is not neat and proper and doesn’t always follow the rules of past seasons. Just because a previous La Nina season had one type of weather pattern does not guarantee that the next La Nina season will feature the same pattern.
Another explanation is that the atmosphere has produced more “blocking” patterns during the last few winters. A block is something the interrupts the normal west-to-east flow of the wind across our latitudes and can easily “mess up” the typical weather patterns.
Heading into mid January, it appears a more typical La Nina type weather pattern will setup, favoring the northern half of the U.S. with more snowfall. But things can change at any time, and based on what’s already happened this season, it is very possible that another round of El Nino type weather could throw down more southern snow before the year is out.
Meteorologist Joel Gratz is the creator of http://www.ColoradoPowderForecast.com and is based in Boulder, CO.