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It’s been well-advertised in our Pattern Predictions, Monthly forecast and “Talking Up a Storm” podcast, but the classic New England winter Matt and Danielle have been touting since December is going to culminate in a classic New England February – with multiple snow events. While Danielle offers full details in our 1DegreeOutside Insights video here, Matt offers some written thoughts, below, to accompany his teammate’s video take:
February has a long history of snow in New England: the first half of the month is historically the most favorable time of the winter for big storms and the month, overall, is the highest average snow of the year. So…it’s not entirely surprising to be looking across the month seeing multiple opportunities for accumulating snow.
As the jet stream trough shifts west, fast air aloft favors storm development in the East.
On the big picture, this is something that makes a lot of sense and we discussed in our monthly forecast both in January (teasing ahead to February) and at the start of this month: after several weeks of a jet stream trough carving out cold and dry air across the Northeast and New England, forcing the storm track to the south, a relaxing of the intensity of the cold should allow warmth and moisture to push a bit farther north than it did in January, thereby shifting the storm track north, as well. Meanwhile, well to our north – north of Hudson Bay, in Canada – the Polar Vortex continues to swirl. This semi-permanent low pressure feature houses a large chunk of cold air in the Northern Hemisphere, and as it swirls and gyrates, it sends shots of intense cold southward. One of the reasons Danielle and I have been referring to this winter as an “old fashioned” Northeast winter is because of the consistency of this Polar Vortex. Over the past several years, the abundance of warmth in the Northern Hemisphere has broken the Polar Vortex into fragments, resulting in wayward drifts of amoeba-like domes of intense cold send fracturing southward in bursts, sputtering amidst a warm North Pole. This year has been different – for the first time in many years, we’ve seen the Polar Vortex remain intact, and the result has been colder-than-normal temperatures in the Northern Tier of the United States. In fact, in January, that cold air was simply too dry to allow moisture to penetrate from the south. Now, that’s changing.
As we head toward mid-February, the Polar Vortex weakens slightly and wobbles west. (Image Courtesy WeatherBell.com)
The biggest driver of changes ongoing in the atmospheric configuration is the subtle but noteworthy weakening and westward wobble of the Polar Vortex. This has allowed for two things to happen in response: the weakening has eased the flow of cold and dry air to New England, allowing the abundant moisture flowing into the Lower 48 from the Pacific and the Gulf of Mexico to become more available to the Northeast, while the westward wobble that is set to unfold in the coming two weeks directs the heart of the cold and dry air toward the Northern Plains, Great Lakes and Midwest – and that’s a meaningful shift to increase our snow chances. The key to that shift is found at the jet stream level. Keep in mind that the jet stream is the fast corridor of air flowing about 30,000 feet above our heads that steers our storms and is driven by the clash between cold air to its north from warm air south of the jet stream. If you’re deep into the cold air, like we were for much of January, you’re too far removed from the storm track. So, to shift the cold air west means the dip in the jet stream – called a “trough” – is also shifting west. This favors snowstorms in New England both because it puts us under the storm path and because it allows warmth and moisture to rebound north ahead of the axis of that deepest trough of cold air. Aloft, something important happens, too: east of that trough, the air high in the sky accelerates out of it. As a metaphor, think of putting your thumb over the end of a garden hose: as the water flows past your thumb it slows down slightly, only to accelerate rapidly once it emerges and sprays ahead. The same principle applies to the fluid of air in our atmosphere – the increasing speed of air aloft coming out of the jet stream trough sprays into the Eastern United States. This is where considering the atmosphere as the three dimensional structure it is, is important – if you’re accelerating air aloft in the Eastern United States, that creates a vacuum of sorts – air must fill the void left by accelerating winds. That air can’t come from above, because you’re already at the top of the weather-forming layer of atmosphere (called the troposphere), so, instead, that air must fill the vacuum from below. In other words, being ahead of the jet stream trough and under the accelerating winds results in a general rising motion of air and, remember, rising air is what we need for storms.
Think of a pot of boiling water on the stove: as the moisture heats up, the steam billows out of the pot, rising quickly. Consider a similar phenomenon here, particularly in light of the atmospheric journey we just examined: warmth and moisture is spilling north into the Eastern United States…it’s encouraged by what’s going on at the jet stream level to rise…and the result is enhanced cloud, precipitation and storm production. In other words, the result is a more favorable setup for storms! This is the long, sordid tale of why, for two months, we’ve been cautiously encouraged by the pattern, and now it has become a reality. The truth is, this pattern certainly could have broken down. Any number of factors could have altered the trajectory, not the least of which would have been an all-too-familiar in modern-times splintering of the Polar Vortex during the winter. But, that didn’t happen, so here we are, in a pattern that doesn’t favor multiple blockbuster blizzards (though we couldn’t rule one out!) but certainly favors snow. The reason you’re not assured multiple multi-day storms in a pattern like this is because the jet stream is more favorable, but is still very fast, overall. The trough, even though shifting to our west, remains rather broad, and this ensures the jet stream winds will keep flowing quickly around it, encouraging storms to keep moving. So, you’re left with Pacific moisture traversing the nation, Gulf of Mexico moisture opened up to meet with it, multiple energetic disturbances encountering the broad, rising air east of the trough and turning into strengthening storms, and enough cold air to create snow in New England and much of the Northeast.
The inherent question that follows is: will this be a repeat of 2015? In that season, after a lackluster start to the winter for snow, we turned on the spicket in late January and blasted through February and into March for what was truly an unprecedented snow blitz that delivered a record amount of entire winter seasonal snow in mere weeks. This pattern is unlikely to best that and the reason is largely owing to the fast jet stream flow mentioned aloft. We will get several disturbances, we are favorable for snow and the average of 100 different solutions over the next two weeks alone cranks out nearly 20″ of new snow in Boston and more than that in much of Northern, Central and Western New England…and that doesn’t take into account fluffy vs. wet consistency snow that may change the accumulation rate – that’s just based on an average accumulation setup. So, we know it’ll snow. We know it’ll snow a lot! And in the mountains of New England, to pick up three to four feet of snow in the next few weeks is a possibility! That said, with a fast jet stream, some of these storm chances will develop just a bit too late and be missed opportunities. Some of them will develop just a bit too soon and carry warmth northward for mixes or changes to sleet, freezing rain or rain. So, to get a setup like 2015 would take a Goldilocks setup that we’re unlikely to achieve. But…it’ll be a fun few weeks for snow lovers, it should be an incredible month for skiers and snowmobilers and it will be snowpack that the water table will welcome when it eventually melts and helps our ongoing moderate to severe drought in New England. As it so often does, New England weather is reaching toward equilibrium – so try to enjoy the show while it does…and keep those reports and pictures coming via the “Send To Us” tab on our free Noyes’ 1DegreeOutside Weather app or the Community Gallery page of our homepage! Storms or sun, Danielle and I love to see the view through your eyes. -MN
