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Impactful winter storm likely on Sunday for Roanoke/NRV area; here is a breakdown of its potential

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Snow probability map 011322

This map depicts the probability of at least one-quarter inch of liquid from snow and sleet -- at least 2.5 inches if all snow -- from 7 a.m. Sunday to 7 a.m. Monday. High probabilities exceeding 70 percent, and even a narrow strip of 90 percent from Roanoke south along the Blue Ridge, are not typically issued 3 days before a potential winter storm and reflect high certainty of a significant occurring. Forecast models show liquid-equivalent totals exceeding an inch in many cases, which could translate to more than 10 inches of snow if it doesn't mix much with sleet or freezing rain.

A developing weather situation Sunday carries the potential to be the most significant winter storm the Roanoke and New River valleys and nearby areas have experienced in three years. There is still time for forecasts to move toward a lesser event, but just as much time to edge upward toward a truly historic event. It would be wise to begin considering how to prepare for the likelihood of several inches of snowfall with sub-freezing temperatures across our region on Sunday, possibly capped by sleet or freezing rain in some areas, with continuing impacts into the week ahead. The event breakdown, as it appears on Thursday morning, below:

Setup: A vigorous upper-level low will be digging south-southeastward through the central U.S., then curve eastward across the South before turning north-northeast near the Appalachians. A surface low will develop in response to the upper-level low over Texas and track eastward. This will pull up abundant Gulf of Mexico moisture into deeply wedged Arctic air, pressed southward by strong high pressure over southern Canada, banked against the Appalachian chain as far south as Charlotte or Atlanta. The southern low will either track east and then north to northeast along the East Coast or it will transfer its energy from inland to a new low that forms along the East Coast. Either way, a steady stream of Gulf and eventually Atlantic moisture is expected to flow into deep Arctic air over our region much of Sunday.

Timing: This is looking very much like a Sunday storm, with little or no precipitation expected before sundown Saturday and probably not much until the pre-dawn hours or near sunrise Sunday. It might even hold off reaching Roanoke and northward until mid to late morning Sunday. Some snow showers may linger into Monday morning but almost all of the accumulating precipitation is probably over by about midnight Sunday.

Precipitation types: Unlike every single wintry precipitation event we have experienced in our region since the 12-18-inch snow of Dec. 9, 2018, temperatures will not be on the near-freezing borderline, so there will be no plain rain. It will be decidedly cold, well below freezing, or dropping well below freezing soon after precipitation begins, thanks to the deeply wedged Arctic air from the high to the north. It may even be in the teens. The first 6 or more hours of the event are likely to be all snow in our region, heavy at times, and it may well finish as all snow. Sleet and freezing rain will encroach on the snow area from the south and east across North Carolina and Central and Southside Virginia as the storm system pulls milder air northward a mile or higher above the surface, and there is some chance this enters our region late in the event, depending on how exactly the surface and upper-level features track and evolve.

Amounts: Moisture and cold air both look to be abundant. Nearly all data as of now suggests at least 5 inches of snow in our region with many forecast model runs pointing to the potential for 10 or more inches. This of course is subject to change, either to lesser amounts with more mixing or a drier system, or to a more sure widespread foot-plus storm, still 3 days away. Up to an inch of sleet or a quarter-inch of ice accretion are possible on top of the snow, mainly south and east of Roanoke.

Things that can change forecast: This isn't going to be an all-rain episode, and a total miss is almost entirely off the board, though a much weaker event is still possible if the upper-level wave proves less amplified or if it were to move very much farther south or east of our region than currently modeled. Perhaps the biggest forecast issue is whether or not, and how soon if it does occur, snow mixes with sleet and/or freezing rain. A more northward/westward tracking storm, a late handoff of energy from an inland low to a coastal one, or just stronger warm-air advection aloft or somewhat weaker wedged-in cold air could lead to a snow to mix or snow to ice changeover by late Sunday afternoon or early evening. Such a changeover would lessen snow totals but make driving conditions even more hazardous. It is unclear at this stage if such a mixing or changeover could reach the Roanoke and New River valleys, and even if it does, it may only occur as snowfall is nearing its end anyway. Chances for snow mixing with or changing to sleet/freezing rain increase south and east of our region.

On the flip side, if a track of the surface low south and east of our region become more certain, snow expectations could rise to 12+ areawide pretty quickly.

Aftermath: Temperatures will likely get above freezing in the mid 30s to lower 40 with sunshine in the early to mid part of the coming week, but nighttime lows will remain in the teens and 20s. Whatever accumulates Sunday will be around for a while, going through cycles of partial thawing and refreezing. If higher end amounts are realized it will be days before more outlying roads can be cleared. Widespread power outages are not anticipated, but there could be scattered ones just from snow accumulation, and any ice on top of the snow would raise the specter for more. The next two weeks appear likely to be colder than normal with possibly a period of very cold weather by the second week of the period, and additional rounds of wintry precipitation will probably develop, though there is no fixed time for the next potential snow or ice episode just yet.

Preparation: If you have Sunday events planned, including church services, now is the time to consider postponements, cancellations or alternate arrangements, though you still have some time to see how forecasts trend before implementing them. If travel is planned for Sunday, it would be wise to consider moving it ahead a day or delaying it a couple days if that is possible. We should know by Friday afternoon if this is still looking potent or if the threat has waned some. Also, the next three days of dry weather are a good time for everyone to assess winter weather preparedness. Do you have the right snow clearing materials at home? Are you prepared for power outages? This is not expected to be as much of a heavy wet snow as Jan. 3 but those could develop with a lot of snow or if ice becomes involved. If traveling, are you carrying warm blankets and clothing, food and water in case you become stranded, as many did on I-95 on Jan. 3?

If this storm proves to be something toward the lower end of its potential, that preparation is still good for the next storm down the line, or to retain for a later season. A bad winter storm, be it snow or ice, will hit our region sooner or later.

Sunday may be that “sooner.”

Contact Kevin Myatt at kevin.myatt@roanoke.com. Follow him on Twitter @kevinmyattwx.

 

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Since 2003, Kevin Myatt has penned the weekly Weather Journal column, and since 2006, the Weather Journal blog, which becomes particularly busy with snow. Kevin has edited a book on hurricanes and has helped lead Virginia Tech students on storm chases.

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