Sunday December 11 – A Freezing Rain Advisory has been issued to include central Maryland north of Baltimore between midnight and 7 AM on Monday December 12. This will be a marginal event, but worth the mention for those traveling in the northern suburbs and across southern Pennsylvania. Will it impact school? That is questionable… But the places to be concerned now include in Maryland: northern Harford, northern Baltimore, Carroll, and Frederick Counties. Also across southern Pennsylvania for Adams, York, and Lancaster.
Temperatures will be near freezing at the surface while warmer air arrives aloft. Computer modeling can have trouble identifying the conditions at the ground. Consider the hills and valleys can vary temperature a few degrees and some cold pocket could remain to have a wet drive turn icy as you turn the corner.
The snow that fell Sunday morning helped to cool down the ground and the air aloft. There was some stickage but the snow had melted shortly after it stopped falling. This sublimation and evaporation chills the ground and holds the cold in a more moist air layer above. That is one reason I mentioned this morning that I thought the icy conditions would spread farther east than models and NWS were suggesting.
The NAM Model shows the freezing line cutting through northern Harford and Baltimore Counties, Carroll, western Howard, and Frederick Counties in Maryland. This lines up with the Advisory map shown above.
It is likely there will be some icing, but main roads will be thawed and passable for the Monday morning commute. Let’s look at the forecast temperatures overnight. These are at specific locations and does NOT include the colder pockets that are likely in between
Temperatures will be gradually warming during the morning. Typically this early in winter, the influence of elevation and proximity to the warmer Chesapeake Bay makes a difference snow or ice vs just rain. That lines up with I-95 or the foothills to the mountains compared to the flat coastal plain around the Bay.
The Canadian Model was overblown with snow a few days ago. While that was too much, it still has held on to the more icy solution for a few days, and shows it here. This shows more of a wet snow set up, which means colder at cloud level. NWS is suggesting up to 1 inch of snow and a glaze of ice in PA supporting this. Meanwhile the conditions in Maryland will have a more shallow layer of air allowing snowflakes to melt, but cold air at the surface could freeze for a few hours on contact.
NAM Model —>slider
This model does not show the full extent of cold air and ice east of the mountains. But the intensity of the precipitation is why I am sharing this here. Moderate rain likely during Monday morning….