The reason for the enhanced ice is a warm layer of air a few thousand feet up that will come from the south on Tuesday afternoon. This is called an overrunning event. Surface temperatures will stay below freezing, but liquid precipitation will fall and freeze either on the surface (freezing rain) or just before it hits the ground (sleet). Here's how the 6z GFS played out with this:
Click any image for a larger view.
On the surface chart, the 0 degree line stays near the KY/TN border on Tuesday morning, meaning below freezing temperatures at the surface.
On this 850MB (5000 feet) chart, the 0 degree line is just south of Louisville, and should go slightly north of the city by Tuesday afternoon. The longer this line stays north of here and surface temperatures stay below freezing, the more ice we get.
The NAM model is going colder with this storm, suggesting all snow for us. I don't know if I buy that because it seems to be portraying an outlying solution compared to the GFS and Euro. With that in mind, I still think we'll see 4-5" in Louisville by Tuesday afternoon, with a fairly thick layer of ice to top that off. More snow is possible on Tuesday night and Wednesday morning, but I don't think we'll see more than an inch or two from that. Southern Indiana will get more snow than ice; Central and Southern Kentucky will get more ice than snow.
So, we're dealing with a mixed winter storm at the moment. If the 850MB charts change, we'll see either a larger snow portion or a larger ice portion of this storm. Either way, it's going to be a mess. I'll post tonight if anything changes in the models.
1 comment:
Hope you guys get more snow then ice. It looks like a borderline event for ice or a cold rain here. I'd like to see the wintry side of it, but ice is the worst form of winter weather to have for anyone, anywhere.
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