Potentially Historic Blizzard Taking Aim on New England

By: Bob Henson , 6:30PM,GMT on January 25,2015

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.


Figure 1. Surface winds (knots) projected by the GFS model at 06Z Sunday, January 25, valid at 09Z Tuesday, January 27. As the surface cyclone winds up south of Long Island, winds exceeding 50 knots are projected to batter Cape Cod. For winds in mph, multiply by 1.15. Photo credit: WunderMap.


It appears that all of the classic ingredients are lining up to produce a historic nor’easter snowstorm. Temperatures on Sunday morning across southern New England were near or slightly above freezing, but a weak cold front is pushing through the area, steered by a separate branch of the jet stream over eastern Canada. This cold, dry low-level air, plus the storm’s track being far enough offshore, will ensure that nearly all precipitation falls as snow for the duration of this storm across the entire region. The main exception is the outer reaches of Cape Cod and Nantucket, where a periodic changeover to rain is possible.

How much snow?
The heaviest snow totals are likely to occur along a SW-to-NE belt oriented from somewhere near or just east of New York City to eastern Massachusetts in or near Boston. In situations like these, narrow strips of intense snow (mesoscale bands) are typically oriented along an upper-level “bent-back” warm front that arcs west from the consolidating storm. Wherever these bands set up, snowfall rates can easily exceed 3”/hour. It’s impossible to predict the exact location of the bands this far in advance. However, mesoscale forecast tools such as NOAA’s new High-Resolution Rapid Refresh model (which became operational just last fall) should provide more detailed guidance by late Monday.

Given the projected intensity of this storm, as well as the strong model agreement and the textbook nature of the overall pattern, it seems very plausible to expect widespread snowfalls from Monday night through Tuesday night of 12” to 24” between northern New Jersey and southwest Maine, with some areas in mesoscale bands getting 24” to 36”. Lesser amounts can be expected further to the southwest, with Philadelphia possibly getting a few inches on top of its Monday total. If the system moves more slowly than expected, it could add to the accumulations on the southern and western flank of the vast snow shield. Massive transportation impacts can be expected over the next several days, with reverberations to the air-traffic system nationwide. The high winds and snow could lead to large-scale power outages across New England.


Figure 2. Snowfall from this week's storm at some New England sites could rival the amounts produced by Winter Storm Nemo, shown here in its full glory at Auburn, Massachusetts, on the evening of February 8, 2013. Photo credit: wunderphotographer stoneygirl.

The most recent analog event for this week's storm is the Blizzard of 2013, aka Winter Storm Nemo, which dropped 24.9” in Boston (the city’s fifth highest snowfall on record) and a storm maximum of 40” at Hamden, Connecticut. The strongest banding and heaviest snowfalls in Nemo extended from central Long Island across eastern Massachusetts to southwest Maine, where Portland had its highest-ever storm total (31.9”). This storm is somewhat less likely to produce massive totals in Maine, but the amounts in southern New England could be comparable to Nemo in places. Only a slight difference in the orientation of the mesoscale banding can make a big difference in whether a particular spot gets a major snowstorm or a record-smashing one. If either Boston or New York gets 20” or more, this week’s storm will make it into either city’s top-ten list. This outcome appears somewhat more likely in Boston than New York, based on the latest models. Current NWS forecasts are calling for 12-24” in New York and 18-24” in Boston, with higher local amounts possible. Since cold temperatures are assured with this system, the snow-to-liquid ratios could be on the high side for nor’easters, which would enhance the expected snow totals further.

Jeff Masters and I are keeping a close eye on this unfolding situation. We’ll post an update by Monday morning.

Bob Henson


Figure 3. “Plumes” of projected total snowfall for Boston, based on an ensemble of more than 20 model solutions compiled at 09Z on Sunday, January 25 by NOAA’s Short Range Ensemble Forecast. The dark black line indicates the model mean, which suggests that 25-26” of snow is a strong possibility for Boston. Photo credit: NOAA Storm Prediction Center.