Thursday, April 24, 2014
December is off to a chilly and slippery start with icy roads in places the past few mornings. Meteorological winter began December 1st and ends February 28th. Those 90 days are the coldest of the year. For much of the country, the months of December, January and February also provide the bulk of snowfall for the winter season.
If you live in a cold climate, you want to know the forecast for the upcoming winter. Pure curiosity, budgeting for heat, a love of snow, a hatred of the white stuff or just to see if “they” get it right all might contribute to see what winter predictions are saying this year.
One of the aspects of the winter which isn’t part of the forecast is perception. If you don’t mind the cold and we don’t receive a lot of snow that might be an easy winter for you. If you get into a car accident because of icy roads, it may cloud your memory of the winter towards it having been worse than it truly was. November certainly seemed like it was a very cold month, but only by less than 2 degrees and not in the top 10 coldest.
Winter forecasts are made for two main variables, precipitation and temperature. The official forecast, which calls for either of these variables to be above or below average, can be thrown way off by one big snowstorm or a week of super cold or extremely mild weather.
Long range forecasts are anything but perfect, however they are getting better. One of the main drivers in our daily weather is the many global circulation patterns which exist. Meteorologists call these long-term patterns teleconnections. These teleconnections “reflect large-scale changes in the atmospheric wave and jet stream movement, and influence temperature, rainfall, storm tracks, and jet stream location/ intensity over vast areas.”
These patterns fluctuate over periods of time. Some patterns change on a weekly basis, while others can be more stable only fluctuating in periods of months, years or decades. The size of these patterns can be vast and their affects global in scope. Some patterns span the entire North Atlantic and over to Europe, others are concentrated in the oceans south of the equatorial regions.
Not all patterns are present the entire year, some are and some only show up in certain months. Additionally, some of the patterns have a bigger effect on the winter months, while others are less a factor. Below is a list of many of the various patterns we know about. You can click on the names to link to an explanation of them if you are interested.
Certain patterns are known to have a bigger influence on our weather here in New England than others. One of the more studied teleconnections is the NAO. When the NAO is negative we tend to be stormier and colder, when the NAO is positive we tend to have less severe winters. During the 1950s and through the winter of 1978/79, the NAO was mostly negative. A big change then occurred and the NAO went mostly positive. This is one reason so many winters in the 80s and early 90s were not so terrible.
This year the Pacific patterns seem to be having a greater control on the weather and one of the reasons arctic air has been spilling into the country so early.
In addition to these patterns, there are others like El Nino and La Nina which have a tremendous influence on our weather. Currently, the planet is showing a more neutral state where neither La Nino nor El Nino is very strong.
When forecasting the upcoming winter meteorologist looks for signals to see how all of these patterns may interact. In some winters, there are signals that many patterns are pushing the atmosphere towards a wet winter, while in other years the signals point to a dry, but mild winter.
Two winters ago many signs indicated a mild winter and that is exactly what happened. Last winter, several signals pointed to a snowy winter and we certainly had one. This year, the indications are somewhat murky, but point to less snow than last winter in New England, but a bit more in the mid-Atlantic. Philadelphia only had about 8 inches of snow last winter, but should better that this year
For this month, I am expecting the cold to relax somewhat after the middle of the month. In other words, it is possible the first part of December could be colder than the second half in some parts of the country; this will likely be true in the Midwest. Snowfall appears limited for now, but just a slight change in the track of one storm can quickly give an area over 6 inches of snow, it doesn’t seem wise to say there won’t be much snow in December, although signals are leaning that way.
The rest of the winter looks to be quite variable with fluctuations between deep cold and milder than average. What I tend to be able to do with reasonable accuracy is forecast when we are entering a stormy or colder period and when we might be in more of a lull or thaw. For example, we know some very cold air will be entering the country this week and may end up affecting the second week of the month. I don’t see any blockbuster snow here in southern Maine before mid-month.
I am still concerned about being in a drought which would lend to a drier, but overall colder winter period. This is similar to the way the winter turned out a decade ago. Back in the winter of 2002 and 2003, we ended up with just over 60 inches of snow in Portland, below average while enduring weeks of below normal temperatures. A deep cold without a lot of snow can be horrible for plants and pipes when the frost goes into the ground very deeply.
December can be cold and often is, but we haven’t had prolonged record breaking cold in over a generation. When you start seeing a long-term temperature trend like this, it’s highly unlikely it’s going to change this month. The last really cold winter season was back in the winter of 2002 and 2003. That year, the average temperature for the winter was the 11th coldest since the late 1800s. Years of bitter cold like that are less common in the past 30 years. This doesn’t mean we won’t experience brutal cold this month, it’s all about the longevity of the cold.
The number of snow/ice events and their size tends to be clustered in years. Once a snowy pattern takes hold, they tend to stick for about 6 weeks. If an area falls into a snowless pattern, that tends to stick as well. Finally, last winter ended up being very snowy. It’s very unusual to have two back to back significantly above average snow years, so this winter, while certainly having some snow, isn’t likely to be one you’ll remember for the final numbers.
Gardening this week
This week I look at making your own swag for the winter season with greens from around the yard.Tweet
David Epstein has been a meteorologist for more than 25 years. He spent 16 years in Boston and currently freelances at WGME13 in Portland.
In 2006, David founded GrowingWisdom.com, a business producing educational and marketing videos for the green industry. He currently is a professor at Framingham State College, teaches Jan Plan at Colby College and owns Bloomscapes Inc., a landscape design business.
David authored "Gardens Of New England" and his work has been published in Grolier's Science Annual for 10 years. He lives in South Natick, Mass., and has a summer home in Harpswell.