Winter’s Comeback

2021-02-09 14:13:00.000 – Sam Robinson, Weather Observer/Engineer

 

Just a few weeks back at the beginning of January, the ground was mostly bare at the base of the mountain and at our North Conway weather station, the monthly average temperature was 7 degrees warmer than normal. The warm start to winter was also felt at the summit, where temperatures had steadily run 5 to almost 20 degrees above normal for the first half of the month, and only 5 days below normal occurred during the latter half. Cold, winter air was nowhere to be found. It seemed to be the talk of New England, as we are normally used to bitter cold, and snowy storm systems. Ski country was hurting. Then scientists and meteorologists alike started murmuring about a phenomenon called the polar vortex. There seemed to be hope in the near future.

Fast forward to today, February 9th where we have just gotten through the first full week of the month. Snow has fallen on the summit every single day so far, and valley locations have seen a generous amount of snow as well. The change was apparent in southern New England too, with my hometown on the Southern New Hampshire border already receiving more snow in the first week of February than December and January combined. The forecast for the near future is also looking promising for more cold and snow with several chances in the next week. Sure enough, the change was brought by the polar vortex, a large area of low pressure and cold air surrounding the poles of the Earth. In our case it was the polar vortex over the arctic, or north pole. Back in mid-January when the hype about the polar vortex started, climate scientists had noticed a stratospheric warming event over far northern Asia. In order for the strongest arctic air over the North Pole to affect us in the continental United States, a force must act upon it to send it wavering southward towards us. This stratospheric warming event that occurred was the needed force and at the beginning of February, the vortex became unstable and expanded southward, specifically over the Midwest United States.

Also following the edges of the polar vortex is the jet stream, which naturally follows the counter clockwise direction of the low pressure from the arctic (basically west-to-east). As the vortex wavered south across the Midwest, the jet stream followed suit and dipped down putting the northeast at its right (east) exit zone. As weather systems enter the Pacific Northwest they hit the jet stream and travel southeast along it before rounding the corner and heading northeast towards us. Adding to the favorable storm tracks is the abnormally warm waters of the Atlantic Ocean. When systems hit the Mid-Atlantic coast, they can grab large amounts of moisture from out over the ocean before heading “Nor’east” towards New England. This fuels these systems with plenty of moisture and the combination of cold air from the west and moisture from the ocean sends snowy, winter storms our way. Another contributor to snowy weather for northern and western New England is the mostly ice free Great Lakes. Most people think of areas like Michigan or Upstate New York when it comes to lake effect snow but it actually affects parts of Western Massachusetts, and Northern Vermont and New Hampshire too, when conditions are right. This year in particular, the lakes are abnormally warm and relatively ice free. When winds come from the west and funnel cold air over the warm water, lake effect snow is produced which can sneakily stack up at higher elevations in the northeast.

That was my best interpretation of this winter’s weather patterns so-far and the polar vortex. If you are interested in learning more about the polar vortex and the interactions between ice and the atmosphere check out the latest Home of the World’s Weather Live program on our YouTube channel at this link here: https://www.youtube.com/watch?v=zxRqDx33oq8 . At the time of this writing, it is snowing up here on the summit and more is in the forecast for the next week. As a snow lover, I am grateful for the pattern change and hope it sticks around for a while. Remember to bundle up if enjoying all the new snow, and thanks for reading!

 

Sam Robinson, Weather Observer/Engineer