In the middle of a winter that seems to continually overproduce at the final buzzer comes another storm system, expected to develop late tonight into early Wednesday morning, that is expected to bring moderate snowfall to much of the Northeast states. It is really quite remarkable how many storm systems have trended more wintry in the final moments during the first half of this meteorological winter, and this storms system will be no exception. Occurring during a pattern transition, with warmer air moving in to the Northeast, it will feature challenges in terms of precipitation type.
A weak low pressure system is already in the process of developing off the Southeast US coast this morning. This low pressure area is mainly associated with an offshore baroclinic zone, or temperature gradient, near the Outer Banks of the Carolinas. Increased precipitable water values are noted on observations and forecast soundings, and models suggest this low pressure area will gradually organize later today.
Meanwhile, a deep trough will dig over the Central United States and is expected to amplify through the Mississippi Valley. As it turns towards the coast, and vorticity advection occurs near the coast, lift in the atmosphere will increase along the baroclinic zone and the low pressure system will deepen while heading north/northeastwards towards the Long Island coast. Precipitation is expected to develop to the west of the low pressure, near a frontal boundary, across the Northeast states later tonight.
Initial precipitation will be light, but steady, across parts of Pennsylvania and New England. But as the storm system gains some steam, banding is expected to develop across parts of New Jersey, Southeast New York and Connecticut and spread into New England. Without any prevalent high latitude blocking, the system will remain mostly progressive. But wintry precipitation amounts could still be significant in some areas, particularly across the interior.
One of the biggest forecast challenges tonight will be temperatures. While plenty of cold air exists aloft, forecast models are consistent in suggesting that the boundary layer will remain quite warm. The boundary layer is the low level atmospheric profile — where we live. And if it is warm enough, snowflakes can melt before they reach the ground. With an onshore flow (wind off the water) prior to the storm, models suggest this will be the case for much of Eastern New Jersey, Long Island, and Southeast Connecticut — mostly a cold rain.
Just inland, however, bands of snow are expected later tonight, and the potential exists for several inches of snow. While quick moving, models suggest enough dynamics for moderate snow in these bands, with quick accumulations of 3-6″ and possibly amounts higher than that in the highest elevations of Northwest NJ, Northeast PA, Southeast NY and New England. The winter storm is expected to be moderate impact in these locations, with a lighter impact event in NYC and even lighter along the coastal plain.
The National Weather Service has, accordingly, issued Winter Weather Advisories for many locations. These create a good visual as to where the impacts are most likely and expected. In these regions, plan for winter weather tonight, including 3-6″ of snowfall, and leave extra time for travel through Wednesday morning when the event finally comes to a close.
The good news? Much warmer weather is anticipated over the coming days, with temperatures 10-15 degrees above average by this weekend! More details to come on that — we have a snowstorm to get through first.