UPDATE 11:45 AM: It appears from radar/model trends that precipitation will move into Southwest Virginia near sunrise on Tuesday. With clear skies in the evening, some temperatures have dropped a bit lower than forecasts. Some bounce upward may occur with the onset of cloud cover, but it may have fallen just enough for a bit more widespread sleet and ice in the morning hours. Temperatures should still rise above freezing in most places by mid to late morning. END UPDATE
A winter storm warning has been posted late tonight and Tuesday for Floyd and Carroll counties, where a quarter inch of glaze ice is possible as sleet and freezing rain move in. Winter weather advisories are up for the remainder of our region as some sleet will change to spotty ice and then rain on Tuesday.
If you’ve lived in Southwest Virginia for several years, you know by now that the high terrain of Floyd and Carroll counties, often extending into the Bent Mountain area of extreme southern Roanoke County, is very often the bullseye for ice storms. As recently as Dec. 26, much of this area was suffering power outages and was iced in for days when most of the rest of Southwest Virginia experienced what was mainly just a nuisance mixed precipitation event. The Blue Ridge widens into more of a plateau in that region, rather than a sharp ridgeline, so it can be harder to sweep cold air away as it clings to the rolling and raised terrain, somewhat protected from southerly winds by even higher mountains to the south and southwest. It’s also susceptible to the easterly upslope winds lifting additional moisture, providing cooling with the lift even when the winds are blowing out of a “warm” southeast angle, and trapping cold air against the east side of the Blue Ridge even when it begins to be scoured out around it. It’s also just south enough to experience thicker moisture earlier in most events than locations farther north, which may have more time to warm above freezing before the bulk of the precipitation arrives. For these reasons, Floyd and Carroll counties have been placed under a winter storm warning for heavy ice, though even at that, it appears to be a low-end warning with a quarter-inch of ice accretion – the bottom boundary for an ice-inspired winter storm warning – expected in some spots. The National Weather Service ice accretion forecast map (scroll down on this link) shows exactly how spotty the icing early Tuesday morning is expected to be, with some spots like the floor of the Roanoke Valley seeing little or no appreciable ice and some higher elevations seeing a tenth or more of ice.
Precipitation will begin moving into the region in the pre-dawn hours Tuesday, likely as a mix of rain, freezing rain and sleet, as evaporational cooling (precipitation drying and evaporating in dry layers of the atmosphere aloft, using heat in the evaporation process, and thereby cooling the air) brings temperatures to the 30-34 degree range across most of Southwest Virginia. The cooling may be deep enough to change all precipitation to sleet for a while at any location, allowing some sleet accumulation, maybe even a few wet snowflakes for a short time. Once warming aloft sweeping ahead of the low tracking well to our northwest (full extent of its effects on mulitple states listed here) takes hold in the upper layers, all precipitation will change to rain or freezing rain, depending on surface temperatures at specific locations. Slow warming should allow almost all locations to be rain by late morning – perhaps excluding a few stubborn iced-in spots on the Blue Ridge south of Roanoke and others where cold air becomes trapped between ridges north and west of Roanoke. Rainfall totals near an inch are expected across most of our region.
A windy, unseasonably cold regime with periodic snow showers – several days of snow squalls piling up inches in West Virginia’s high terrain, bleeding into some of the typical “snow belts” in the 3,500+ elevations of Virginia along the West Virginia border and west of I-77 – sets in late Wednesday through the weekend. There is some chance a stronger low tracks to our south by the middle of next week, with colder air remaining in place. It’s too far out to put much stock in, obviously, but the setup is favorable enough for a winter storm that it can’t be completely ignored, either.