Early Spring or Late Thaw?

Brutally cold temperatures have been the norm as Arctic high pressure has been dominating our weather this week. Piles of snow abound the landscape. Well, this is all about to change as the overall weather pattern takes a turn for the warmer. 

January has been one for the record books as the snowiest month ever in the historical records (going back a hundred years). The news has been dominated with stories of roof collapses and a lack of places to put snow. Places where the snow has not been cleared, there is now an inches thick glacier that no amount of sand or salt is going to erode.

So what has been the cause of this seemingly harsh winter pattern? Blame La Niña. This phenomenon causes unusually low sea surface temperatures across the equator in the Pacific Ocean, disrupting the jet stream. This pattern tends to lead to a stormier winter across New England. For us, a La Niña winter typically means somewhat higher snowfall accumulations, and more ice storms, although they don’t usually occur all within 35 days.

La Niña does not tell the whole story. An anomalously strong negative NAO is responsible for bringing us our recent stormy pattern and intrusions of bitterly cold Arctic air. What the heck is an NAO? I’ve heard this term batted about on the local news stations recently with nary an explanation, and it drives me nuts when people use terms like this and don’t bother to give a decent explanation of them. 

The NAO stands for North Atlantic Oscillation, and described the relationship between two seasonal features that dominate our winter weather, namely a low pressure system situated over Iceland/Greenland, and a large high pressure system located over the Sargasso Sea (also known as a Bermuda High). When the NAO is negative, as it has been thus far this winter, the high is very weak, and the low is very strong (in fact it the low has been unusually strong), and this allows cold air to intrude our latitude and allows for a stormy pattern for New England. When it is positive, as it looks like it is becoming, the high becomes the dominant feature, and this acts to pump warmer tropical air northward to us.  

After some snow showers on Sunday, temperatures will rebound into the 40s through much of next week, possibly eclipsing 50 for the first time this year by the weekend! This is certainly a welcome and refreshing change from our January experience.

The longer range modeling indicates that the NAO will be positive for at least the next week. After that, there are signals that the NAO will take another turn for the negative, once again plunging us into a stormier pattern.  Acting in our favor will be the fact that sun angle is steadily increasing (as we are nearing spring), and this will act to keep winter from having as icy a grip as it has had on us. One or two more snowstorms cannot be ruled out as winter heads into the home stretch, but rest assured that this winter’s days are numbered.