An Icy Day for Most

Wednesday, December 16, 8:30 AM

No big changes from last night’s update, though I think that many of us are in for a long duration sleet event. East of 95 still looks like it will warm enough to change to rain, but we have to see how far west the warm air makes it this afternoon. There is not model consensus on the placement of the storm which translates to lower confidence in the forecasts. I feel confident that warm air will nose in to the mid levels in the areas along and west of 95 causing snow to change to sleet, but I don’t feel confident that the surface temperatures will be scoured out. As a result, sleet could be the predominant precipitation for most of us from mid afternoon into the evening. And it could be heavy. Most models have the mid levels warming even in northern MD and as far west as Frederick, but we can only wait to see if they’re right. If so, those areas will also see sleet. Regardless, for most areas west of 95, although it won’t be a classic snow storm, this will be a high impact event so be careful.

One other thing that I mentioned in last evening’s update was the the low possibility of cashing in on some backside snow love. Just a quick and simple primer, as the storm approaches from the south, counterclockwise winds around the storm will be from the east or even southeast. That’s the kiss of death because relatively warmer air rotates in from off the ocean. We want north and northeast winds. East and southeast winds invade the mid levels causing snow to change to sleet, and eventually warms the surface so sleet goes to rain. But once the storm gains enough latitude, winds shift to northeast, north, and eventually northwest (that’s why it generally gets colder and drier after a storm). Anyway, a couple of days ago models were suggesting that when this storm got enough latitude to shift the winds back to the north and rapidly cool the mid levels back below freezing, there was remaining moisture that was modeled to fall as snow. Since then, the global models have backed away from that idea, but the possibility is still there, especially in the northern areas. If that situation develops, or if there are any surprises (fingers crossed), I’ll update again.