After a warm and relatively dry winter and early spring, April brought snow!
A huge April Nor’easter slammed the Northeast and Mid-Atlantic states. Some areas got over a foot of snow!
More than 75,000 people were left without power.
What in the world is happening? Why did this happen?
Here's some insight . . .
Happy April! SOURCE: NOAA
Blame it on the NAO, the crossing guard of the Atlantic. The North Atlantic Oscillation is an air pattern that allows cold Arctic air to whiz across the Atlantic. For most of this winter, it has been either positive or neutral. This meant that it either stopped the cold polar air from entering North America (a positive NAO) or allowed it to leave the continent very quickly (a neutral NAO).
Blame the NAO, the crossing guard of the Atlantic, for the snow. Credit: Microsoft
Now it is negative.
The North Atlantic Oscillation is shaped by air pressure. When the low-pressure atmospheric area around Iceland is similar to the high-pressure around the warm Azores Islands in the mid-Atlantic, it forms a negative NAO. This air pattern blocks cold fronts from crossing the Atlantic. Cold front after cold front enters North America and lingers. The temperatures drop and the frozen air plunges south.
The negative NAO is keeping cold air from crossing the Atlantic SOURCE: NOAA
At the same time, the Gulf Stream is flowing very fast, heating the ocean water off our shores. The air above the ocean is very warm and wet. This warm, wet air is flowing up the coast and has set everything up for a classic Nor’easter. When the Arctic air hits it, it is like a car crash. The Atlantic air cools and all the moisture falls out.
Unfortunately, for some of your gardens, some of this fallout is snow, lots and lots of snow. Indeed, the amount of snow is record-breaking in some areas, including Central Park in New York City. However, this is a spring storm, not a winter blizzard. Most of the precipitation will be much needed rain for the thirsty Northeast.
Most models seem to indicate that the negative NAO will not last very long. The NAO will be alternating between positive and negative over the next few months. With luck, we will get rain and then more warm, balmy weather. It all depends on the crossing guard of the Atlantic.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.