One of the most impressive bands of snow we've seen in a long time developed over a narrow swath of the Northeast overnight Friday into early Saturday, creating an intense snowfall gradient over very short distances.
A fast-moving low-pressure system tracked out of the Midwest toward the East Coast through the day Friday, producing heavy snow along its path from St. Louis to New York City.
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| A radar snapshot from around 1:30 a.m on February 17, 2024 (RadarOmega) |
This wasn't an ordinary clipper system, though. While weak systems like this tend drop a few inches of snow before moving on their way, we saw a dramatic band of snow develop on the northern side of the low.
The band left behind enhanced snowfall totals from Indiana to New York, reaching its peak intensity over portions of Pennsylvania and New Jersey.
A tremendous gradient sliced through Allentown, Pennsylvania, with folks on the south side of town witnessing 13" of snow while neighborhoods north of town saw just 3" of snow. Farther east, observers measured 10" of snow in Brooklyn, while only 2" of snow fell in Central Park just a dozen miles to the north.
Even more impressive is that parts of New Jersey saw snowfall rates of 5" per hour at the peak of the snowfall. This kind of convective banding is something more like what you'd see off the Great Lakes rather than eastern Pennsylvania and northern New Jersey. Instead of lake-warmed air fueling intense bands of snow, we saw intense frontogenesis along the northern side of the low.
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| Frontogenesis in the mid-levels of the atmosphere early Saturday morning. (NOAA/SPC) |
Frontogenesis occurs when an airmass on the move collides with another airmass nearby. This interaction creates a stretching motion through the atmosphere. Winds slowing down and fanning out leaves a 'void' in the atmosphere that air has to rush upward to fill, a rising motion that creates a convective band of very heavy snowfall.
We often see this process during classic nor'easters when a shield of very heavy snow develops on the northwestern side of the storm. But it's not limited to nor'easters—conditions were just right for this relatively weak system to generate the intense dynamics needed to drop a tremendous amount of snow across a narrow stretch of real estate.
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