48 Hours of Snow Coming! Forecasting the Nor’easter on Tuesday

25 01 2015

It is going to be an extremely eventful next 72 hours for the region and the northeast as a whole.

As a mentioned in my last post, a small clipper system will pass through the area late tonight and tomorrow. This storm has the stereotypical features of a clipper: plenty of cold air, fluffy snow, a general 2-4 inches for most. Precipitation will start falling late tonight and continue throughout the day tomorrow.

NAM Model Monday

NAM Model Monday

At this point, the situation gets complicated. After the clipper exits the coast, it will interact with a weak disturbance off the Atlantic coast and strengthen rapidly into a nor’easter. Plenty of moisture will be fed into the storm from the ocean, and plenty of cold air will be present as well. The question that remains is where and when this storm will strengthen. Models have been a little inconsistent with the timing of the phase and where it will occur. The further west the storm phases, the more snow we will receive in the Philadelphia area. In New York City and Boston, blizzard conditions will be likely.

Model Analysis:

European: The European has been the aggressive model for this storm. Most of the solutions it shows bring the storm close to the coast and drop 10-15 inches of snow with totals higher in New Jersey and areas closer to New York.

European Model

European Model

GFS: The GFS model has been the more conservative model, showing a slower phase further east than the European. It’s latest runs have been having convective feedback issues, however, which means it’s solution may not be accurate. Until these issues are resolved, I will not be favoring this model when making my forecast.

NAM: The North American Model is the middle ground between the two previous ones. It is projecting 8-12 inches falling by Wednesday morning. I am favoring this model the most out of the three because of its increased accuracy in the short run.

NAM Model

NAM Model

Timing :

12 AM-6 AM Monday: Snow will start west to east

6 AM- 6 PM Monday: Snow accumulating a general 2-4 inches during the day

6 PM Monday- 2 AM Tuesday: Light Snow as storm strengthens off of coast

2 AM – 5 PM Tuesday: Snow. Heavy at times. Accumulating 5-8 inches (or more depending on location of storm off coast)

5 PM Tuesday – 3 AM Wednesday: More snow, eventually tapering off late night on Tuesday

The official Forecast:

While the clipper forecast is fairly straight forward, the following nor’easter involves many dynamic components which need to be ideal for a major snowstorm to occur in the Delaware Valley. Even though these conditions are favorable, there is still some uncertainty in the exact amount of snow we will receive by Wednesday morning. Temperatures will be in mid-20s, which means a light fluffy snow will fall. These low temperatures also increase the snow to precipitation ratio, which means snow will accumulate faster than normal.

The snow map below shows totals from the clipper and the nor’easter combined. Depending on the formation of the low off the coast, the 10-14″ area is subject to shift in the next day or two. Overall, 6-10″ inches is good bet for the city and areas south and west. Totals will be higher closer to NYC and even higher near Boston, where blizzard conditions will likely occur.

Snow Map for the One Two Punch

Snow Map for the One Two Punch

Effects on travel will be significant on Monday and Tuesday. Businesses and schools will be shutdown on Tuesday, and I wouldn’t count out some cancellations on Monday as well. Stay off the roads and be safe. More

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updates coming.

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