The average temperature at 9am this morning across the continental US was 18.0°F which was nearly a degree colder than the lowest average CONUS temperature recorded all of last winter – and winter hasn’t even begun yet. While much of the nation has been in a deep freeze, the Mid-Atlantic region has been quite mild for the past couple of days, but colder air is now oozing into this part of the country following the passage of an Arctic front. Around here, our temperatures will continue to gradually drop this afternoon and evening as rain continues to fall from one wave of low pressure riding along the stalling Arctic frontal boundary zone. By late tonight and early Saturday, it could get just cold enough in the northern and western suburbs for the rain to mix with or change to ice and/or snow before ending early Saturday. More significant snow will fall later tonight across places like central and northeastern Pennsylvania and skiers will be happy for that.
After a break in the action on Saturday, a classic “cold air damming” event will take place on Sunday and Sunday night in the Mid-Atlantic region where cold air funnels southward from high pressure situated to the north. Snow is likely to break out in the morning across the DC metro region, then by mid-afternoon in Philly, and by early evening in the NYC metro region. The DC region could see snow accumulate in the 2-4 inch range before a changeover to sleet and freezing rain adds a singificant layer of ice on top of the snow. The Philly and NYC metro regions could see snow accumulations on the order of ½ to 2 inches before a changeover to sleet and freezing rain adds a significant layer of ice on top of the snow in those locations. Travel conditions will no doubt be adversely affected for an extended period of time during this event in much of the Mid-Atlantic region from Virginia to New York as temperatures hold at or below the freezing mark and significant icing results. Ultimately, by late Sunday night/early Monday, the wintry precipitation changes to plain rain along the immediate I-95 corridor and to points south and east, but it is still a pretty close call and frozen precipitation will very likely last into early Monday just to the north and west of the big cities.