Its shaping up to be a fairly icy day after Christmas for many across the Mid-Atlantic states Friday into Saturday. A classic “Overrunning Event” to unfold as a warm front moves into arctic air that’s trapped across New England forced by northeast winds ahead of the precip.
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 guidance at this time, areas closer towards the Mason-Dixon have the greatest threat for looking at snow and ice accumulations as the cold air will be locked up better in those regions. totals wise at this time is not for certain the amount of snow/ice is expected with this system as we get a bit closer in time. Areas across Central Delmarva will start off with that wintry mix but eventually change over to plain rain as the winds turn a bit more easterly which will bring in that warmer Atlantic air across the region.
