Wednesday March 20, 2013 | 08:18 AM
Posted by David Epstein

This morning we are waking up to 6 to 14 inches of fresh snow on the ground. I know the world looks like the middle of January for many of us, but just after 7 a.m. this morning astronomical spring arrived. A question I got quite a bit yesterday was “are we done with winter?”  Other folks asked me why this winter has been so different from last year’s.  I think the answer to both of those questions is related, so let me briefly address them.

I'll be updating my weather forecast for this week on Twitter at @growingwisdom please follow me there. Feel free to comment or ask questions too.

Winters across North America are highly variable. Here in the northeastern part of the country our winters fluctuate quite dramatically from year to year. Reliable records go back to the later part of the 19th century and since then how much snow and cold occur one year is often different from the previous or the one that follows.  

There are many meteorological factors that exist across the planet with oscillating phases. Depending on the phase, they can push an area towards colder or warmer temperatures, drier or warmer conditions.  I like to think of them as levers that get pulled by the atmosphere.  The different positions of the levers give us a good indication of what the general weather patterns will be.  The image below shows two such variables since 1900.

The tough part is that the levers have an almost infinite number of positions and when they all interact with one another it can become difficult to predict the outcome. One of these oscillating variables, and perhaps the most influential here in New England, is the North Atlantic Oscillation, or NAO. The NAO, when in a positive phase, often brings mild weather with fewer coastal storms to the region. When the NAO goes negative the opposite happens.  Since February the NAO has been negative and the major reason for all the cold and snow. The NAO is reasonably well forecast about 2 weeks into the future. Current forecasts keep the NAO negative through the end of the month and into April. This is part of the reason I am bullish on colder than normal temperatures to close out March.  (image below)

There are many other patterns like these that meteorologists and climatologists are constantly evaluating.  The Pacific North American Pattern or PNA, the El Nino Southern Oscillation or ENSO, the Arctic Oscillation or AO, the Pacific Decadal Oscillation or PDO, The Madden-Julian Oscillation or MJO, and the Atlantic Multi-Decadal Oscillation or MDO are just a few.  If you were to do some quick Google research on any of those variables you would not only see the current state of them, but also how they play in the overall weather and seasonal variability. 

The image below summarizes the AO's two phases.

 

These oscillations are what many meteorologists believe are the primary drivers of climate and one of the many reasons you will often find meteorologists at odds with the theories of climatologists. Most climatologists would argue that anthropogenic warming will flip the phases of these oscillations more than would otherwise be observed. It’s an interesting, yet unproven scientific question. Unfortunately, this nuance often gets lost in the shouting between those who feel man is the primary driver of climate and those who don’t. This is also an oversimplified explanation of a very complicated issue. This isn't to say humans don't affect the climate in profound ways. My point is about the human interaction with these oscillations which clearly drive our weather so profoundly.

Just take one look at the average snowfall for New England over the past several decades and you will see one reason why I don’t get too excited when snowfall fluctuates so wildly from one year to the next. The media tends to play up big weather events when in reality these big weather events are nothing new.  They make it seem as if the events are becoming more frequent and stronger, yet the statistics for events like wild fires, drought, tornadoes, and hurricanes really haven’t changed.

This March has been acting similar to 1956, 1960, and 1967 in terms of similar oscillation patterns. Forecasting this way is based on looking for analog years or years with like patterning in the global system.  Last year was very similar to 1936-1937 when we had a very hot summer followed by a nearly snowless winter.  This year is acting like some winters from the 50s and 60s.

Also, just because one month is behaving like the analog for previous year doesn’t mean the following month will too.  However, I do think that the colder and snowier than normal pattern is going to continue into April.  This doesn’t mean I am predicting an April snowstorm; rather the trend for cold and possible snow will remain firmly entrenched. The image below shows that much of the eastern part of the United States is forecast to be cold for the next two weeks.

 

Gardening this week: A very common problem with house plants is aphids. These sucking insects leave a residue on the leaves that can then cause a secondary infection on your plants. If you notice a black shoot-like coating on your houseplants, you probably have black sooty mold. This problem, while not generally fatal to a plant, can be an indication of an insect infestation. Check out this week's video on black sooty mold and see if your plants have this issue.

I'll be updating my weather forecast for this week on Twitter at @growingwisdom please follow me there. Feel free to comment or ask questions too.

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About the Author

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.

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