December 26-27th event has been a model guidance nightmare these past few days so that’s why i haven’t really talked much about it. Because at one moment its a 63 degree day with rain and then next minute its a day with accumulating snow and ice. This is very typical back and forth nonsense that happens in the 84-120hr timeframe so i don’t put a whole lot of weight to it. But we are starting to get into the sub 84 timeframe where they begin to get their act together. So here is the setup.
We will already have a push of arctic air in place out ahead of a weak disturbance with a warm front nosing into the cold air. This is a classic representation of what we call a “Overrunning Event”
An overrunning event in winter meteorology occurs when warm, moist air is lifted up and over a shallow layer of cold air at the surface. This setup is common ahead of winter storms and often develops north of a warm front. Because cold air is denser, it remains trapped near the ground while warmer air flows over it along sloping isentropic surfaces.
As the rising warm air cools, clouds and precipitation develop well in advance of the main storm system. In winter, this frequently leads to widespread, long-duration precipitation, often falling as snow, sleet, or freezing rain, depending on the temperature profile of the atmosphere. Overrunning events are typically associated with stratiform precipitation, lower visibility, and steady rather than convective rainfall or snowfall.
These events can produce significant winter weather impacts, including heavy snow accumulations, ice accretion, and hazardous travel conditions, especially when cold air is reinforced at the surface by high pressure to the north. Overrunning precipitation often marks the initial phase of a winter storm before stronger dynamics and surface low pressure move in.
With the latest mid day mid range guidance rolling in they are starting to come into light of a icing scenario beginning to unfold across areas of central and northern Delmarva, northern Maryland, and portions of South Jersey. A lot of factors remain in place like will the cold air remain more locked in and keep the warm nose at bay, will the warm nose make it a widespread icing event, or will the warm nose overwhelm the environment and keep it more of a rain threat in the region. Those are the details we need to iron out going later into the week.