Here's What To Know About The '40/70 Benchmark' And Northeast Snow

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Forecasting snowfall in the Northeast can be tricky, partially because the exact track of the winter storm makes a big difference. The “40/70 benchmark” is often brought up when discussing the storm track, so here’s what you need to know.

W​inter Storm Lorraine is one of those winter storms that will track near the 40/70 benchmark and increases the confidence that moderate to heavy snowfall is likely in areas of the Northeast near the coast, including the I-95 corridor.

B​elow, we take a closer look at what different tracks near the benchmark can mean for Northeast snowfall.

T​rack Near The Benchmark

First, the 40/70 benchmark refers to a location on the map at 40 degrees north latitude and 70 degrees west longitude. This spot is shown on the map below as the white dot where the two lines meet.

In general, when cold air is available over the Northeast, a low tracking through this general point on the globe is the sweet spot for delivering a heavy snowfall event to at least parts of the region, often areas closer to the coast.

A​reas farther inland will typically see lighter snow or no precipitation.

T​rack West Of The Benchmark

I​f the center of low pressure moves west of the benchmark or closer to the Northeast, warmer Atlantic air is ushered into the region. This means rain is more likely near the coast with heavy snow possible farther inland.

However, exactly where that rain/snow line sets up can be difficult to forecast. There can also be a sharp snowfall gradient with a foot of snow to a few inches or even all rain occurring over a short distance.

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T​rack East Of The Benchmark

When the center of a winter storm tracks east of the benchmark and farther from the Northeast, this often means lighter snow near the coast or perhaps no precipitation at all. This eastern track can leave the colder air in place but moisture from the system may be too far away to bring much snow.

L​ocations farther inland will likely miss out on any snowfall in this scenario.

Linda Lam is a lead meteorologist at weather.com. Growing up in Massachusetts, she developed a fascination for winter storms and hurricanes that led her to pursue a career in meteorology.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives.