12:00 PM | Ice threat for awhile tonight N and W; couple of snow threats later this week

Discussion

Very cold air dominated the weather scene for much of the weekend and consequently the ground has become quite frozen. Meanwhile, precipitation has broken out in the Tennessee Valley at the front end of some milder air that is advancing towards us here in the Mid-Atlantic region. This milder air will initially encounter some stubborn cold air around here that will be somewhat reluctant to give up its ground. Also, the air in place is very dry throughout the lowest levels of the atmosphere which will lead to significant evaporational cooling at the onset of the precipitation. As a result, as precipitation breaks out later this evening, temperatures may be just cold enough in the lower levels of the atmosphere for some sleet and/or freezing rain. The most likely timing for the potential icing is between about 10PM and 3AM, and the most likely locations for this include the upper parts of Bucks and Montgomery Counties and Northern Chester County. Enough mild air should move in aloft to prevent any appreciable snow from falling during this time period. Towards morning, the warmer air will win out at ground level and “plain” rain will fall on an occasional basis through the day Tuesday and some of the rain can come down hard for a while. Looking ahead, there are a couple of threats for snow here later this week. First, light snow is possible Thursday night from a fast-moving weak system dropping southeastward from Canada, and then more snow is possible Friday night/Saturday from an even stronger southern system that will head towards the Mid-Atlantic coast early this weekend. And if you really want to see some snow, head to Mount Ranier, Washington where 150 inches could fall over the next several days as the Pacific Northwest gets absolutely pounded this week.