Tuesday, January 15, 2008

48 hours and counting...

It's not a 'classic' winter set-up by any means, but Thursday could easily have it's set of travel woes when a wintry mix of snow, rain, and sleet move into the Piedmont of North Carolina early in the morning. My question to viewers is "how little accumulation do you think is needed before there are big traffic problems?" In the case of frozen precipitation, even less than an inch can be a problem, especially the way a lot of people drive (read 'irresponsibly'). Limited accumulations are likely.

The storm system itself has far from fully organized yet, so we are all going over the myriad data/model runs and discerning our own 'markers' as to what we envision the situation to be. So much to look at, keeping in mind they are not 'what will happen' scenarios but 'what could happen.' And so I isolated last night's GFS run for Thursday morning and added some notes to the graphic below (click to enlarge):


In the models for the past couple of days, the storm system has stayed on it's track from the TX Gulf coast over to the FL panhandle and up the Coastal Plain on the Atlantic seaboard. Too, the timing has been consistent run to run, with 'likely' precipitation in Charlotte before sunrise and closer to sunrise in Greensboro Thursday.

An 'iffy' part has been the necessary high pressure to the north - while it's on the map above it's not solidly in place on many other maps. You need that high to the north to drive in the N/NE winds that will build a cold wedge in the Piedmont while the moisture streams over the top of it in the opposite direction. Without that high in place, not enough sustained cold air gets fed in and the temperature will warm to above freezing in this case.

With that said, the most recent ETA MOS data (as I write) has the high/low for Charlotte at 33/30, which is colder than Greensboro's 36/32, and bit of a chin-scratcher for me. I'll need to sift through more data this morning to see if that trend disappears or, if not, what's going on in the model to cause that cold bull's eye to show up farther south like that.

It will be in and out in one day, with warmer temperatures moving right back in for Friday (briefly). I think there will be light accumulations early Thursday morning before a cold, cold rain dominates by 10am. The AM commute could easily have slippery problems. The PM commute should just be all a cold showery mess. Refreeze could be an issue Friday morning.

Them's my thoughts for the moment. FYI, Sunday is your cold day of teens to start and 30s for highs, with a slight but immediate warm-up Monday.

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