A rare May nor’easter is bearing down on New England Thursday afternoon and evening, packing strong winds that could top 40 to 50 miles per hour at times, especially along Massachusetts’ South Shore, Cape Cod, and the islands.
We think of nor’easters as colossal snowmakers in the winter, but the name comes from the wind direction — winds coming from the northeast as the counter-clockwise spin of the storm lurks just offshore. The term “nor’easter” was actually first used in print in 1836 by folks in the marine industry, such as sailors or shipping merchants.
This New England storm setup is pretty rare this time of year. We see nor’easters most commonly during the winter because there is a more drastic temperature difference between cold and warm air masses, which can lead to the jet stream becoming very volatile. In other words, the jet stream is more wavy during the winter, and the more wavy it becomes, stronger storms may form. And should the jet stream align near the coast, then boom, we can have a nor’easter.
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We’ve seen this pattern a few times this spring, where a strong Northern Atlantic high-pressure blocks or slows down storms from exiting the Northeast, causing the jet stream to buckle south over the eastern portion of the country.
Below you can see how the jet stream is positioned more south today, typical of a classic winter setup, leading to the birth of the nor’easter:
Nor’easters can wreak havoc when combining strong winds with heavy precipitation — both rain and snow. The storm usually gains strength over the Gulf of Maine, as the right quadrant of the storm taps into plenty of moisture from the Atlantic, geographically unique as the Gulf Stream funnels warm water north. This can lead to feet of snow during the winter or flooding rainfall that we may see on Thursday. Check out the deep green moisture funneling into the storm, below.
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The last significant nor’easter to hit New England during May was back in 2008.
Ken Mahan can be reached at ken.mahan@globe.com. Follow him on Instagram @kenmahantheweatherman.