The densely populated area from New York City to Boston could experience one of its ten biggest snowstorms on record early this week, as a textbook nor’easter takes shape over the next 48 hours. While local details are bound to evolve somewhat as the storm develops, the models are now in strong, consistent agreement on a potentially crippling snowstorm. Blizzard watches were hoisted on Sunday morning from eastern New Jersey to northeast Massachusetts, including the New York, Providence, and Boston metropolitan areas. Despite the increasing skill of computer forecast models in recent years, this week’s threat emerged remarkably quickly. As recently as Friday, the model consensus was for a weaker storm that would sweep through the region from west to east, then strengthen well offshore. One of the first models to switch gears was the ECMWF, whose operational run issued at 00Z Friday night highlighted the risk of a potential blockbuster storm for the Northeast U.S. By Saturday morning, most other models had quickly joined the bandwagon. “All operational models now have the forecast of a major snowstorm/blizzard,” said NOAA’s Weather Prediction Center on Sunday morning.The driver for this record-threatening event is a strong upper-level wave now diving across the Midwest. In line with the pattern of several other storms this year, this wave will produce a stripe of snow from northern Indiana and Ohio into Pennsylvania, dropping several inches on the Washington and Philadelphia metro areas by Monday afternoon. On its heels, a powerful branch of the jet stream will continue diving southeastward, intensified by a unusually strong ridge over the western U.S. that produced record highs across Washington, Oregon, and California on Saturday. As it moves off the mid-Atlantic coast, the upper-level energy will consolidate into a powerful upper-level low and generate a rapidly intensifying surface low. Surface pressures may drop by more than 24 millibars in 24 hours, qualifying the storm as a true coastal “bomb". Sea surface temperatures are well above average off the northeast U.S. coast, which could help fuel the storm’s strengthening. As it reaches peak intensity on Tuesday, the surface low is expected to slow down just southeast of Cape Cod, which would keep the snow machine going at full strength and lash the New England coast with winds gusting to 60 mph or more in places.
By: Bob Henson , 6:30 PM GMT on January 25, 2015