Over the past several years, I have put out numerous early and final winter forecasts for the United States with some of them being spot on and some of them not. When doing my research for the upcoming winter, I always come across countless winter forecasts that have been put out by amateur and professional weather forecasters, and it doesn’t matter how much experience a weather forecaster has, the majority of winter forecasts end up being wrong.
Do Meteorologists Weigh Too Heavily On El Niño and La Niña?
The one thing that I have noticed over the last five years is that forecasters weigh too heavily on one variable: ENSO (El Niño/La Niña). Now don’t take that the wrong way! El Niño and La Niña can have huge impacts on the winter months in the mid-latitudes (United States winter), but there are MANY other variables to consider. Like you’ve heard me say many times, the strength of El Niño/La Niña and the placement of the warmer/cooler waters across the central and eastern Pacific can be a determining factor as to how heavily ENSO needs to be considered for that upcoming winter in the United States.
Most of you have heard of the NAO (North Atlantic Oscillation) and the AO (Arctic Oscillation). It’s something you hear more about during the winter months, and these are two indices that can heavily impact temperatures and precipitation each winter across the United States. NAO/AO are often considered by most meteorologists and long-range forecasters as wildcard factors, and something that can’t be accurately predicted beyond a 1 to 2 week period. If you’re relying entirely on forecast models to make that prediction for you, then that statement is generally true.
Can Siberian Snow Cover In October Be An Accurate Predictor of the United States Winter?
Since around 2009 or 2010, I have been following the work of Dr. Judah Cohen, the director of seasonal forecasting at Atmospheric and Environmental Research (AER). Dr. Cohen has numerous peer-reviewed publications on the impact that Siberian snow cover has on the upcoming winter months (December, January, and February), and his research shows that the rapid extent of snow cover over Siberia in October can impact the phase of the NAO/AO for that winter.
With that said, one must realize that the Siberian snow cover extent in October alone can’t accurately predict the upcoming winter temperatures across the eastern United States. When you just consider the snow cover extent, only evaluate the monthly value, and include all of Eurasia, the correlation between snow cover and the winter AO is not as strong. Notice the correlation coefficient on the graphic below is 0.41 (a correlation coefficient of 1 would be perfect positive linear correlation).
Dr. Cohen and his team have come up with an index called the Snow Advance Index (SAI). The SAI uses daily (instead of monthly) values of snow cover extent over the entire month of October and only considers the region south of 60 degrees north. Notice how the correlation coefficient is nearly 0.86, which shows a strong correlation between the SAI index and the winter AO. This index shows that the rate of snow cover change over this region has a bigger impact on the winter temperatures across the United States vs. the snow cover extent by itself. The negative values on the graphic below would indicate a snowier and colder winter in the eastern United States.
So How Is Everything Looking For the 2014-15 Winter?
Siberian snow cover is already rapidly expanding, and based on forecast model guidance, that trend is going to continue throughout the rest of the month. Because the SAI considers daily snow extent values, Cohen and his team will not make any predictions until after this month is over. Remember how cold the 2013-14 winter was?? Well, October 2013 had the 4th highest snow cover extent over Eurasia (Siberia) since 46 years of records began. As of October 13, 2014, 12.2 million square kilometers of Eurasia were covered by snow compared to 10.8 million square kilometers around this same time last year. We’re already way ahead of what even occurred last year!
October 1976 holds the record as having the highest Eurasia snow extent of 17.2 million square kilometers! We all have heard about or remember the notoriously cold 1976-77 winter that broke countless records. In recent years, the 2009-10 and 2010-11 United States winters were heavily impacted by the negative phases of the NAO/AO, which caused bitter cold across a large chunk of the U.S and numerous East Coast winter storms.
We could be heading down that same road again this winter, but we still have two more weeks to go in October. A lot can change in two weeks, but as I stated above, model guidance suggests that this snowy trend over Siberia is going to continue.
I am planning to release my final 2014-15 winter forecast on November 2nd! Before that forecasts comes out, I am going to do a “part 2” of this article explaining exactly how Siberian snow cover expansion can lead to a negative NAO/AO winter, and therefore, bring with it a brutally cold and snowy winter for the eastern United States. Please understand that Siberian snow cover is only one variable that I consider when putting together my final winter forecast.
Please be sure to like the Firsthand Weather Facebook page, where I plan to keep everyone updated on whether or not the Siberian snow cover continues to rapidly expand the second half of this month!
Matthew Holliday (Curriculum Vitae - Resume) is a graduate of the University of Oklahoma, where he completed a B.S. in Meteorology and a B.S. in Geographic Information Science. He completed his master's degree in meteorology and climatology at Mississippi State University and is currently pursing a Ph.D. in Earth and Atmospheric Sciences.