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Here’s why we aren’t expecting blockbuster snow totals in NYC

Much has been made over the past few days in regards to the potential for a major snowstorm in the Mid Atlantic and Northeast this weekend. With up to two feet of snow (possibly more in banding) expected in the Washington DC area, and the storm forecast to move at least slightly north up the Mid Atlantic coast, there have been an increasing amount of forecasts calling for prolific snowfall amounts in New York City. But forecast models over the last day or so have again begun trending southward, with a very sharp gradient in precipitation expected near the New York City Area.

In fact, further investigation of the changes on forecast models reveal several atmospheric developments that are disconcerting for big snowfall — and it seems likely that New York City will avoid the blockbuster snowfall amounts at this point. Here’s why:

A collapsing West Coast Ridge

That darn ‘old Pacific Jet. We’ve spoken about the Pacific Jet many times this year, but it seems to be making its presence especially known during this storm system. A large West Coast ridge develops later this week, with its center axis near the Rocky Mountains. This feature is critical to the initial development of the storm, as it allows it to amplify south/southeastward into the Mississippi River Valley.

GFS model showing a large mid level trough over Southeast US later this week, with a weakening ridge out west.

GFS model showing a large mid level trough over Southeast US later this week, with a weakening ridge out west.

But the ridge itself begins to get beaten down by a large, anomalous trough in the Eastern Pacific and Gulf of Alaska. This causes the ridge to roll eastward, allowing our storm to remain slightly more progressive. Instead of coming northward up the coast, the storm has a tendency to press east-northeast once it reaches the latitude of the Mid-Atlantic Coast. This is just enough of a progressive “push” to leave our area out of the prolific snowfall totals.

Confluence, and a compressed height gradient to the north

Over Southeast Canada is a large vortex, also known as a 50-50 low (near 50 longitude and 50 latitude), which is helping to keep cold air entrenched in the Northeast US during this storm threat. Over the past few days, models have trended more anomalous with this feature, with more shortwave energy over New England and to the Northeast of Maine in the Northwest Atlantic Ocean.

In short, this compresses the mid level atmospheric height field to our north. It creates a tighter gradient to the north of the developing storm, and the resistance doesn’t allow the amplifying storm as much room to move northward. Instead, the storm “stalls” near the Mid-Atlantic coast, and then shifts northeastward out to the Atlantic Ocean.

Occlusion, and an upper level low too far south

Let’s make no mistakes here: This is a powerful storm system being depicted on every single forecast model. This storm develops toward the Lower Tennessee Valley, and then reforms off the Southeast United States Coast. In the mid and upper levels, a powerful phase is occurring, forming a large and powerful mid and upper level low. This low “cuts off” from the jet stream near the Southeast and Mid Atlantic Coast.

GFS model showing a tremendous cutoff in precipitation totals near the NYC Region by the time the storm ends on Sunday.

GFS model showing a tremendous cutoff in precipitation totals near the NYC Region by the time the storm ends on Sunday.

Why is that important? When mid and upper level lows “cut off” from the jet stream, they also lose the dynamics of the jet stream. These are the dynamics that drive storm development. So the storm, essentially, matures near the Mid-Atlantic coast, and then begins to drift northward. This will help to force the mid level fronts north toward our area as well, with some precipitation, but the dynamics are more than likely to be short lived.

What this means is that while our area will see precipitation, the mid and upper level low cutting off too far south mean that we’re also likely to see less impressive dynamics. Poor snowflake production, some dry air in the mid levels, and a decaying low pressure system mean that heavy snow totals are likely to be spotty.

What do we make of all of this? 

Let’s focus on the word “blockbuster”. What we’re trying to get across with this article is that the big snowfall totals in this storm (12-18+ inches) are likely to remain confined to areas south of Philadelphia, including Southern NJ and toward Washington DC and the Mid Atlantic. Near the NYC Area, including Long Island and Northern NJ, the snowfall amounts are currently expected to be much more moderated.

Even then, a sharp cutoff is expected — over the northern suburbs, just a few inches of snow is possible, while nearer to NYC and just south of there, several inches of snow may still fall. The cutoff will be quite sharp and dramatic, with snowfall changing in just a few miles from north to south.

Snowfall numbers aside, the storm is still likely to be impactful. This is especially true for coastal areas, where models continue to indicate an impressive east/northeasterly wind fetch. This will lead to the potential for coastal flooding and strong winds, with flooding potentially working into the back bays along the New Jersey Shore. If you live in those areas, we recommend taking the typical precautions to protect life and property.

Additional articles will be posted today with details on the hazards this storm is expected to bring to the area, including specific snowfall totals and coastal flooding information.

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