With the amount of daylight fading a couple of minutes each day, it is time to start thinking about the winter outlook.
This winter appears to have a similar feel as the last couple, with the overall idea being a season that is colder than normal. To get an idea of how the winter will play out, we look at several factors. Among them are the water temperatures in the Pacific and Atlantic Oceans, recent jet stream patterns, early season snow cover in the high latitudes of the Northern Hemisphere, current levels of soil moisture, and wind velocities in the lower stratosphere.
It is a lot to go through and analyze. Much of what I have learned regarding seasonal forecasting over the past several years I have gleaned from colleagues that do this type of forecasting on a much more regular basis. It is only fair to acknowledge their contributions. Dave Tolleris, Corey Lefkof, Matt Lanza, Jeff Manna, and several others who forecast specifically for businesses and commodities, have helped lead me in this direction. And I am most grateful for their insight.
One of the more intriguing developments I came across this season is from Tolleris. He has begun to draw a link between hurricane landfalls and the conditions during the following winter. But he cautions, that if there is a strong temperature signal (read: El Niño or La Niña) in the Pacific Ocean, this hurricane link does not work very well.
Given only a weak La Niña is currently in place, and that it is expected to remain at a modest level, this link may be valid this year. The link suggests fewer hurricane landfalls lead to a colder than average winter along the East Coast. And even though there has been a lot of noise this tropical season, the number of landfalls has been lower than the long term average.
With this, and the other factors above, the short version of the winter outlook is cold… at least with respect to normal. How much snow falls is a thornier issue. During the winter of 2009-10, Lynchburg had its 10th snowiest winter on record, when 34.8" fell. Last winter, only 8.4" fell. An average winter brings 17.4".
The coldest month of the season is expected to be December. Not that the rest of the winter will turn suddenly warm, but the worst of the cold, relative to normal, will be at the beginning of the season.
Regarding snowfall, we expect the total to be higher than last year's amount, but lower than the winter of 2009-10. Now, that leaves us a pretty big window, but given the recent configuration of the upper air steering winds and the weak La Niña pattern over the Pacific, I'm guessing the total amount of snow will be greater than average.
So, the guess for Lynchburg is 18-24" for meteorological winter (December through February). A few inches less in Danville… a few inches more in Roanoke.
One other caution. A large driver of temperatures from week-to-week during the winter is a pattern in the northern Atlantic Ocean, called (fittingly), the North Atlantic Oscillation (NAO). Keep an eye on it this season. When it goes negative, that means warm air has bulged northward toward Greenland, and colder air will dive south into the eastern United States.
You can follow the changes in the NAO at the Climate Prediction Center. I will be watching it, that's for sure.