A little ice possible tonight...

Before changing to rain... A cold, depressing, rain...

Today was first real winter-like day of this winter; the snow shower we had today really helped with that. Sadly, once again, it was just a tease. Although the surface temperatures are still cold, southerly flow aloft has brought warm air in.

This is very characteristic of a CAD situation. The cold air stays at the bottom and the warm air overruns the cold. Unfortunately, the high pressure that is supplying the cold air is moving east, and will be replaced with a low pressure system over the great lakes.

Approximate low positions and movement. Red star is Washington DC. Note that the surface winds are still from the north, bringing cold air.

Any precipitation that falls will mostly be liquid. However, where surface temperatures are below freezing, freezing rain and/ or freezing drizzle is possible, forming a glaze of ice on objects that are below freezing. This is not likely to last very long as the cold layer gets shallower and shallower, eventually completely eroding away, allowing freezing rain to become plain rain.

850 mb Temps are above freezing over our area. Winds out of the south at this altitude is responsible for the rise in temperatures. The cold layer is eroding, with a little sliver left up against the mountains.

The 850 mb layer is around 1500 meters in altitude. Generally, if the temperature of the air column is below freezing from 850mb down to the surface, snow will be able to fall. If there is a warm layer that is warm enough to melt the snow between the 850 mb layer and the surface, sleet or freezing rain is possible depending on the altitude of the warm layer.

925 mb temperatures are also above freezing, but just barely. Easterly flow is eroding the cold albeit more slowly.

The 925 mb layer is lower in altitude than the 850 mb layer, around 1000 meters. If temps are below freezing throughout the air column until this point, then liquid will have enough time to freeze and fall as sleet. If the surface is below freezing, but there is a warm layer aloft, then freezing rain falls.

Conclusion:
Don't expect much out of this. The northern third of the county is under a winter weather advisory for sleet and freezing rain. Temperatures will likely be above freezing by morning so no delay expected.