DISCUSSION: There is increasing confidence of there being a short but intense burst of heavier snow across both the Hudson Valley in southern New York state as well as across parts of southern Connecticut during the day tomorrow. This is going to most certainly induce substantial travel delays as this heavier snowfall burst moves through these parts of the Northeastern United States. However, it is also important to understand how and why this burst of heavier snowfall is projected to unfold in the first place. To understand this, it is important to explain to explain a fundamental concept which is directly tied to heavy snow banding within Winter-time coastal low-pressure systems.
This critical process which is directly associated with heavier snow banding which forms in association with heavier snow banding features within Winter-time coastal low-pressure systems (which are also referred to as Nor’easters) is known as frontogenesis. Frontogenesis in the simplest terms is essentially the process by which air-streams in the lower-to-middle parts of the atmosphere converge from opposite directions which forces locally-driven upward motion. When this regionally forced upward motion occurs along a horizontal axis in the vicinity of a coastal or semi-coastal region along a region such as the U.S. East Coast, this will often facilitate the generation of features known as mesoscale snow bands. Mesoscale snow bands are often longer and relatively narrower snow bands which form within larger precipitation (i.e., mostly snow) shields within a Nor’easter and are directly fueled by the low/middle-level convergence associated with strengthened low-level frontogenesis. Thus, the frontogenetic forcing is the primary ingredient which when combined with sufficiently colder air, leads to locally heavier snowfall potential.
Attached above is a recent graphic (courtesy of the Tropical Tidbits website which is directed by Meteorologist Levi Cowan) which perfectly illustrates this concept via the forecast for the North American Model (NAM)-12km 700 hectopascal Temperature (in degrees Celsius), Temperature Advection, Frontogenesis, and Wind for the next 24 to 36 hours. You will note how there is a brighter red-colored band which moves through a good portion of Connecticut and the lower Hudson Valley tomorrow which is the frontogenetic feature which is projected to generate this heavier snow band. Thus, it will certainly be interesting to watch and see how this winter weather event unfolds for these areas and beyond.
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© 2018 Meteorologist Jordan Rabinowitz