Summaries bold-faced below.
Tenths and hundredths of an inch of rain don’t matter that much to most people. The puddles are a little bigger with 0.4 inch of rain versus 0.1 inch of rain, but there’s not a hugely different impact on travel and life in general. It’s very different for snow. That difference in moisture is, on average, the difference in a 4-inch snow and a 1-inch snow, and travel impacts seem to multiply by the inch. The differences in various forecast models are minute, whittled down to a tenth or two of liquid, even a few hundredths. But that difference holds the key as to whether Friday’s snow will be a barely-snow-at-all or something a little more memorable. Winter weather advisories have been posted from the Roanoke Valley and Blue Ridge westward, where snowfall amounts of generally 1-4 inches are expected. The 4-inch amounts more likely to come in parts of the New River Valley and perhaps even more widespread to the west. To the east of Roanoke, snow will likely fall, but current projections are for an inch or less. The reason for the west to east diminishing of snow amounts has less to do with temperature differences (everywhere will be below freezing) or specific elevations (though that will play some factor, as it usually does) as it does with the possibility that the moisture with the system will dry up some as it advances eastward. We’ve talked all week about the very dry air in place with the Arctic air mass, and that will tend to eat away at the snow and reduce its intensity as it moves eastward, especially east of the Blue Ridge. That is, unless upper-level lift is strong enough to overcome the drying effects, which the North American Model has been the most bullish in showing happening on many of its recent runs. The difference in getting a tenth of an inch of moisture and maybe locally a third to a half an inch could be magnified further by getting somewhat better than 10:1 snow-liquid ratios – in other words, when snow forms in colder air, it often develops more intricate crystals that put more air in snow as it collects on the surface, boosting snow totals. So it’s possible at times we could get more than the typical inch of snow per tenth of an inch of moisture. That’s just a further complication to a convoluted forecast.
Bottom line: Expect about 1-2 inches in the Roanoke area, 2-3 inches in the New River valley and westward with some higher amounts, and about an inch east of Roanoke on Friday. Be prepared for the possibility of getting 3-6 inches if the system is a little more robust than most models depict or some locally heavier bands develop. Don’t be shocked if your specific location sees little, if the system dries up more than most modeling shows, or some “snow holes” develop.
Timing should see snow move into counties west of I-77 before 10 a.m and then spread eastward through the New River and Roanoke valleys by early afternoon. The heaviest snow should be confined to 3 hours or so, with flurries and/or freezing drizzle trailing off intermittently into the evening. The farther south you are, the better your chance of seeing some sleet mixing in, especially toward the end of the snow.
Impact on power lines is expected to be VERY LOW due to the likely powdery nature of the snow, but roads will deteriorate rapidly with even several minutes of sustained snowfall, as recent cold weather will mean snow will start sticking quickly on untreated road surfaces.
We may hit 60 degrees by the middle of next week, so if snow isn’t your thing, there’s a break not far away. It won’t last long, though.