www.roanoke.com

Check out the list of observations across Virginia and North Carolina. Note the numbers under "DP," or the dew point. Very, very low numbers in places away from the coast, single digits in many places. Roanoke's was 4 degrees at 3 p.m. A few are even below zero.

The difference in the temperature and the dew point reflects how dry the atmosphere is. With temperatures in the 30s and 40s and dew points scraping zero, precpitation falling into that dry air near the surface will evaporate, taking heat out of the atmosphere. This evaporational cooling is where forecasters expect to get much of the cooling that would be necessary to trigger an ice storm. That cooling will eventually be overcome by warmth moving in from the south, but that may be hours later.

It's another situation where a degree or two could make all the difference. Most of you will probably have some ice in the morning, even if it's just a little on car metal and trees, while a few of you may escape without any ice. I expect there to be about a 4-6 hour windown from 3 a.m. to about 7-9 a.m. where Roanoke may drop to 32 or even 30 or 31. I don't expect huge glaze ice issues on the roads in the immediate Roanoke Valley, but please do be careful driving, as even a small patch of ice can be treacherous. As you fan out from the Roanoke Valley in distance and elevation, conditions will be considerably worse.

Probably just a few showers of rain/freezing rain and maybe some sleet before midnight, with the heavier stuff moving in after midnight.You can follow its arrival on the national Doppler radar loop.

Latest advisories and warnings from the National Weather Service in Blacksburg.