By Jon Moskaitis
The cold front that passed through Cambridge yesterday morning was the first tangible result of a significant pattern change that appears to be taking place in atmospheric flow at the continental scale. For the past five weeks, the northern branch of the jet stream has kept Arctic air bottled up in the vicinity of the pole, allowing temperatures to rise above the climatological average over almost the entirety of North America. During this period, the mean temperature in Boston ran a full 10 degrees Fahrenheit (6�C) above the climatological average. But now the northern branch of the jet stream has moved into a position such that Arctic air tends be exported southwards across North America. This basic pattern is expected to last for at least the next two weeks, leading to cold weather here for the rest of the month.
In the short term, the next round of precipitation is anticipated to arrive on Friday, in between two blasts of cold, dry air. Currently, it looks like this storm will bring mostly rain to the area, but situation bears watching, as small changes to the forecast storm track could lead to snow instead of rain.
Today: Sunny, but cold and blustery. High: 19�F (-7�C)
Tonight: Clear and cold. Low: 8�F (-13�C)
Thursday: Increasing clouds, breezy. High: 32�F (0�C)
Friday: Rain likely, then changing over to snow showers. High: 38�F (3�C)
Saturday: Partly cloudy, windy. High: 30�F (-1�C)
Sunday: Mostly clear. High: 26�F (-3�C)