Every winter has its coldest week and coldest morning of the season. The bottom of the curve is different each year, but it always happens.
This year, the coldest week of the winter is likely the next seven days, with the core of the cold arriving Sunday morning. This particular cold snap will rival the coldest of the cold last February, but the big difference is it won’t last as long.
The reason for the upcoming cold is all about the jet stream. The jet stream is a river of air that carries storms and air masses across the planet. The polar jet stream, which moves south and north repeatedly with the seasons, doesn’t blow straight east to west. Rather, the jet stream gets kinks in it, much like a garden hose. When one end of the jet stream bulges up, the other end dips down to compensate. This is what will happen this weekend; we will be under a very deep dip in the jet steam.
The media will likely say the Polar Vortex has come to New England, or something like that, but the Polar Vortex remains where it belongs up at the poles. The strength and configuration of the Polar Vortex is constantly in flux. Sometimes, when the vortex weakens, it allows some of the cold air spinning around it to bleed south. This has already happened on the other side of the planet this winter, but it hasn’t occurred much around here.
The map below shows the flow of air at 30,000 feet this weekend. Follow the black line I drew and it goes all the way back the pole. It’s cold up there, and a direct flow of air into New England from that regions means there’s not much time for the air to modify, thus the reason for the expected near-record lows this weekend.
Another way to see how the air is flowing is to check if the forecasted temperatures are below average. Highs should be in the upper 30s and lows in the lower 20s this time of year. If temperatures are 20 degrees below average, the lows end up near zero and the highs say in the single numbers.
Watch the animation below. The red colors represent air above the seasonal average, the blue and purples below. Notice the cold air overtaking the region this weekend. Also notice how it doesn’t stick around very long. By next week, temperatures are back to seasonable levels.
There can often be some storminess during these transitions between arctic outbreaks. Once again, models keep the bulk of any snow away this weekend, but there’s a small chance of something developing Saturday morning as the cold really takes hold.
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