UPDATE 8:40 AM, 3/25/2018: Over 70,000 customers (which means homes and businesses, so hundreds of thousands people affected) of Appalachian Power are without electricity this morning after the heavy wet snowstorm focused on areas southwest and south of Roanoke. END UPDATE
UPDATE 2:10 AM, 3/25/2018: Snow is rapidly clearing out of our region after a very high-impact winter storm that has left more than 58,000 customers without power in Applachian Power's Virginia service area, including about three-quarters of its power customers in Pulaski County. Snowfall accumulation of 8-16 inches were common in a swath across the New River Valley, the I-77 corridor and the Blue Ridge south of Roanoke. The Roanoke Valley escaped the worst effects of the storm, though by early evening snow had covered many roads in the southern part of Roanoke County where some amounts up to 8 inches occurred, even as some other parts of the valley got little accumulation. As was stated many times here, it was all about where the heavy snow bands set up in the evening hours, and that was ever so slightly southwest and south of the Roanoke Valley. There will be much to look back on with this remarkable winter storm. In the meantime, expect temperatures to remain cold relative to late March through Tuesday, but highs in the upper 30s to mid 40s will help begin melting the snow on Sunday. END UPDATE
UPDATE 12:30 AM, 3/25/2018: You may remember I said something about snow bisecting the Roanoke Valley -- the radar image posted above clearly shows that, with continuing moderate snow bands moving east-southeast over the southern half of the valley while the northern valley has lighter snow. Several models this afternoon suggested this possibility, and the snow totals are going to reflect quite a spread from very little in the north and some lower elevation areas near the Roanoke River or downtown to some over 6 inches in the southern part of Roanoke County. My location just south of Roanoke is now over 3 inches. There are a number of spots in Roanoke in the 1-2-inch range. ... To the south, its not 1-2 but in fact 1 and 2 put together, as in twelve, with 10-14 inches reported in parts of the New River Valley and along the I-77 corridor. We have perhaps 2 or 3 more hours of solid snow moving across the region south of Roanoke, edging right up into the valley. Probably several 12-18 inch reports from this storm in a region that has really been considered the likely bullseye for a couple of days. Appalachian Power now reporting more than 60,000 without power in its service area over 3 states, with 50,000 of those in Virginia, including nearly 13,000 in Pulaski County alone. END UPDATE
UPDATE 8:55 PM, 3/24/2018: Extremely heavy snow bands have been focusing on the New River Valley, I-77 corridor and the Blue Ridge south of Roanoke with many locations well over 6 inches and snow continuing to pile up. The heavy wet snow is damaging trees and has caused nearly 19,000 customer outages, and counting, according to Appalachian Power's website. There will undoubtedly be some 12-18 inch totals in that region and most locations will top 8 inches. Meanwhile, the heavy snow band has barely missed Roanoke to the south, leaving the city with fairly light snow that isn't collecting much with slightly above-freezing surface temperatures. Some heavier snow has been moving around the southern edge of the valley where some 6+ amounts and several 3-6 amounts may occur in southern Roanoke Count. Some Roanoke city areas may still get 1-3 inches -- there are some moderate to locally heavy bands moving in from West Virginia that may affect the valley -- but this storm will probably be considered a "bust" for its snowfall totals in Roanoke even while it turns into a legitimate disaster for areas to the south and southwest with widespread and growing power outages. END UPDATE
UPDATE 6:25 PM, 3/24/2018: Snowfall reports of 2 to 6 inches are already common across the New River Valley and southward along the I-77 corridor, and there is much more to come upstream, as the heavy bands expected for this evening are on radar and moving southeastward. For the Roanoke Valley, the precipitation has changed to all snow even into the lowest elevations now, but as yet, little is sticking most places, on some grass in some of the higher parts of the city mostly, though it changes pretty rapidly and gets whiter as you move just south and southwest of Roanoke/Salem cities. The heavy bands moving through during the next few hours will have the potential to quickly ramp up totals just about everywhere from the Roanoke Valley south and west. Many locations in the NRV, Blue Ridge south of Roanoke and along I-77 will top 6 inches in this storm, even into southwest Roanoke County, with it quite likely a few spots hit 10-12 inches. In the Roanoke Valley, depending on how heavy the snow gets and how rapidly it begins accumulating now that the sun will soon be going down, amounts appear likely tor range from 2 inches in the lowest elevations near the river to as much as 6 or even 8 inches in some of the higher elevations rimming the western and southern parts of the city. Heavier snow does not continue far north of Roanoke, and lesser totals are expected as you move north and east. Locations east of the Blue Ridge toward Southside may quickly collect 3-6 inches this evening as these heavy bands move through. END UPDATE
UPDATE 2:45 PM, 3/24/2018: Precipitation began moving into the Roanoke Valley just before 2 p.m. Driving from southwest Roanoke County to downtown Roanoke, I observed some pretty vigorous snow showers in south Roanoke, but a mix of rain and snow in the lower elevations of downtown. As the afternoon and evening progress, more and more of the precipitation will be snow into lower elevations as the temperature cools and we'll start seeing some accumulations on grassy areas first, also working from higher to lower elevations. This is very much looking on track for at least a 4 to 8 inch snowfall in most of the New River Valley and the Blue Ridge south of Roanoke, quite possibly 10-12 in some spots. Many models continue to put the Roanoke Valley right on the edge between heavier snow to the south and more moderate amounts just north, literally bisecting the valley in half in some cases. It will all come down to how heavier snow bands track this evening. Also, it's not settled exactly where the north end of the snow will be, probably 10 to 50 miles north of Roanoke, but could be a little farther than that. Also, do not surprised once again to see lightning or hear thunder during snowfall -- this occurred with this storm system in Iowa last night. END UPDATE
UPDATE 1PM, 3/24/2018: Snow has been reported in parts of the New River Valley and on Bent Mountain in Southwest Roanoke County. These are the preliminary rounds, so to speak -- they won't accumulate much, falling lightly with surface temperatures above freezing, but do serve to moisten the atmosphere and generate evaporational cooling that will lead to heavier snow reaching the surface later. Accumulating snow has been occurring along and west of I-77, with some 2-3-inch reports in Wythe and Tazewell counties. Roanoke's surface temperature is in the upper 30s, but the layers above are below freezing, so the first flakes may reach the surface as snow, though don't be surprised if there are sprinkles if the surface warmth is a little too thick and the flakes melt. Every flake that falls, whether it evaporates or melts or reaches the surface, is helping cool and moisten the atmosphere. Posted above is a radar shot from near 12:45 p.m. with a few explanatory items. This long area of precipitation is being generated just ahead of the battle line between spring and winter -- warmth to the southwest and cold to the northeast. A low-pressure will dive along that boundary tonight, bringing heavier precipitation to the region this evening. Again, New River Valley and the Blue Ridge south of Roanoke, in addition to the I-77 corridor already experiencing accumulating, looks primed for the heaviest snow with some 8-10-inch amounts embedded in a larger area of 4-8. Radar seems to indicate Roanoke probably will be within the northern edge of the heavier snow tonight -- thinking 3-5 inches in the lower elevations (below 1,200 feet) of the valley to 4-8 along the higher elevations, especially in the southern part of the valley. Snowfall will diminish rather quickly north of the heavier snow bands and there may be a hard edge to the snow somewhere north and east of Roanoke -- Covington, Buchanan or so, maybe as far north and east as Lexington to Lynchburg, it's difficult to say, as the current edge may still nudge a little more northeast. The region east of the Blue Ridge and south of Smith Mountain Lake is quite a conundrum, as heavier precipitation bands will likely roll through there this evening, but surface temperatures may lead to more rain mix. ... In the Roanoke and New River valleys, expect a few flakes, maybe pellets or sprinkles, this afternoon with little accumulation, but possibly heavier stuff reaching the New River Valley after 3 p.m. and the Roanoke Valley an hour or two later. END UPDATE
UPDATE 11:15 AM, 3/24/2018: Snow has spread into parts of Southwest Virginia, mainly along the I-77 corridor, around Hillsville and Wytheville, but also into some of the western and southern New River Valley. Quite impressively, snow extends from northwest North Carolina to eastern South Dakota in an unbroken streak, an unusual alignment for winter storm events that affect our region. While cells within the snow band are moving southeast, the snow band itself will ever-so-slowly encroach eastward into cold, dry air today, gradually moistening it. Some flakes may fall in the Blacksburg-Christiansburg area by early afternoon and perhaps in the Roanoke Valley by mid to late afternoon, possibly mixed with rain or sleet, with the more significant snowfall arriving during the evening. Overall, forecasts and warnings for heavy snow tonight look to be intact, though computer forecast model guidance presents some uncertainty in exactly where the heavy bands of snow this evening will set up. The New River Valley and the Blue Ridge south of Roanoke are most likely to experience this heavy snow overnight, and it is probable into the Roanoke Valley, though at least some models paint the heaviest snow slightly south. The northern extent of the overall snow area is also in some question -- the James River or I-64 seem to be possible locations for the northern edge of the snow. Accumulations are likely to top 4 inches where the heaviest bands move through tonight, with lesser amounts just north, dropping off pretty sharply moving northward. Bumps north and south a few miles are still possible, so regions outside the winter storm warning should not presume they are entirely out of the heavy snow potential. Locations already receiving snow will have a head start with a base of snow on the surface before the late March solar zenith and before evening heavy snow. END UPDATE
UPDATE 6:50 AM, 3/24/2018: The National Weather Service has added Franklin and Patrick counties to the winter storm warning, which technically went into effect at 5 a.m., though it will be some hours before more eastern areas in the warning see much wintry precipitation and maybe sunset before much accumulation. The leading precipitation is a lot closer than you may think if you awaken to blue sky or the sun peeking over the horizon near the Blue Ridge, with radar as of just before 7 a.m. showing it moving across far southwest Virginia as far east as I-77. Clouds will quickly cover the sky this morning -- radiational cooling was maximized with a clear, calm night, and the clouds likely cover the sun before it can do a lot of daytime warming -- and that moisture will work east, but it will be bumping into cold, dry air aloft and largely evaporating. Moisture will continue to thicken and reach the surface as a mix of rain, sleet and snow, with some accumulations possible to the west, but probably not much as it nears the Roanoke Valley and Blue Ridge at midday through mid afternoon at the peak of the surface-warming late March sun angle. The heavier precipitation that is the prime impetus for the winter storm warning is still upstream in the upper Midwest and will slide in this evening. As the air layers cool from top to bottom, more snow will reach the surface until it is eventually all snow by evening, and likely quite heavy snow at times. The National Weather Service map above has expected accumulation ranges, which are pretty close to anything I would draw up at this point, and which will vary based on elevation and where the heaviest snow bands set up. Again, if you're close to the winter storm warning boundary in a neighboring county, you may see a similar outcome as locations a short distance away in the warning. I'll keep updating this page from time to time through the day. END UPDATE
Quick update: Confidence is growing from forecast model data that a period of heavy snow will occur in much of our region late Saturday afternoon into the evening and overnight.
Light precipitation may move in as early as midday. This precipitation will be in the form of rain, sleet and snow, as temperatures will rise into the upper 30s and lower 40s in many locations during the day. But as the precipitation rates increase, snow is expected to develop rapidly as the atmosphere cools and it can reach lower and lower elevations in the mid to late afternoon until it covers our entire region. Waves of heavy snow are expected to occur by evening, possibly accumulating at rates of 1 to 2 inches per hour at times in some locations with totals of 4-8 inches and locally up to 10 looking likely for the Roanoke and New River valleys and along the Blue Ridge south of Roanoke westward to the I-77 corridor.
Amounts are expected to taper off north and east of Roanoke and east of the Blue Ridge, but the area of 4+ or at least 2-4 snow may reach a little farther in those directions than the earlier-issued winter storm warning would suggest. Per its forecast discussion tonight, the weather service will make a decision on whether to expand winter storm warnings in the morning.
While this is a wet snow with marginal temperatures, the intensity of it could make travel difficult in many areas for several hours Saturday evening. There is also some concern about tree damage and power outages as wet snow builds up on those exposed objects.
I hope to update this post with a little more detail on Saturday morning and continue updates through Saturday.