A mix of rain, freezing rain and sleet is moving in bands across Southwest Virginia this morning. Most locations are starting out 28-34 degrees. Even though precipitation has started in many locations, cold-air damming is pushing colder and somewhat drier air along the surface, so most locations east of I-77 will see another couple degrees drop in temperature as the dew point dips slightly lower and evaporational cooling of precipitation falling into that slightly drier air brings the temperature down just a bit. The “wet-bulb” temperature, calculated from temperature, humidity/dew point and air pressure, is a measure of what the temperature would be if fully saturated — Roanoke Regional Airport’s wet-bulb temperature was 31.8 degrees at 6 a.m., so it’s likely to get to the freezing mark later today even if the dew point drops no further. It’s possible a few locations may stall at 33 or 34 degrees — if yours does, count yourself blessed (unless you like ice storms) and don’t gloat or bemoan the forecast “bust” too much, because someone not far away from you will be getting ice,, and maybe a lot of it. Temperatures aren’t going to be rising anytime soon — perhaps after dark, as warm air advection finally begins winning the battle against cold air damming — and precipitation will continue to develop and re-generate to our west and southwest and move through. Many forecast models show the heavier precipitation moving through during the late afternoon and evening. Areas generally NORTH of Roanoke seem to be favored for both the most precipitation and more consistent/widespread below-freezing temperatures for a longer period of time — that area may seem some 1/2 inch or greater amounts of ice, increasing the chance of tree damage and power outages. 1/4 to 1/2 inch still appears to be the more widespread expectation for ice amounts, with some spots getting a little more and some getting less. Sleet is not likely to be a major contributor to the precipitation from the Roanoke and New River valleys southward, mixing in sporadically for only a few more hours. Exposed objects will collect most of the ice today, but bridges and overpasses are likely to freeze over in many locations, and other road ways will get increasingly icy especially in locations that dip below 30 degrees. If the road looks just wet, presume it has some icy patches.
Temperatures are likely to get well above freezing Monday, with many 40s readings, so any ice should melt away.