Now is the time to take stock of how prepared we are for a weather event that could knock out power for several days to at least some. We’ve already been through such a weather event on June 29, the derecho that knocked out power to about half of the region during some of the hottest days of the year. As hard as it may be to believe, there is some chance — not a certainty – that Oct. 29 may upstage June 29 in terms of the areal coverage and intensity of a weather event in the Eastern U.S. Whether Southwest Virginia is in a core area for storm effects remains to be seen. We may yet be on the outside looking in for most of what could be a historic weather event to our north and east, but at the very least, we are likely to get some gusty winds early next week — and that alone is cause for concern. If we prepare now, and all we have is some breezy cold next week that shakes colorful leaves off our trees, we’ll be better set for that ice storm with our name on it three months from now.
To recap the setup: Hurricane Sandy has crossed Jamaica today, generally headed north-northeastward, likely to pass east of Florida, where it may start to weaken slightly as it hits cooler water and/or increasing atmospheric shear aloft. That shear will be caused by a dipping jet stream trough over the eastern U.S., which will bring in an Arctic air mass late in the weekend, slamming the door on this week’s warm spell (record high of 78 for Blacksburg on Wednesday; Roanoke just 2 short of record at 83). The jet stream dip, or low-pressure trough, may catch Sandy, absorbing its energy, and converting Sandy into a strong “extratropical” low that would be pulled northwestward into the Eastern U.S., perhaps as far west as the Great Lakes. Sandy is not likely to move out to sea, as we generally expect tropical systems to do this time of year, because of a large low-pressure system in the central Atlantic blocking its eastward movement, and a big high over Greenland blocking its northward movement. As an intense inland low, the former Sandy turned extratropical storm could cause a wide range of weather mayhem — wind, rain, snow, big waves on the coast — from the Ohio Valley to the East Coast, extending north into Canada.
I am using Tuesday morning’s frame from the 12Z European model at left, which I must emphasize, is but one solution to how this could play out, and a rather extreme one. The Euro has been the most consistent model in developing what would be a historic storm system, the one most of the other models are trending toward. The first thing to note about this map is the number of isobars — the black lines, connecting points of equal barometric pressure. When you see these packed tightly, it means lots of wind. Wind is the top concern right now for Southwest Virginia, what we’ll likely get if we don’t see much precipitation. We still have lots of tree with leaves on them — many of those leaves will go flying next week, but before they do, each one acts as a sail catching a little more wind that can tug on limbs and trunks. That could increase wind damage compared to similar winds later in winter with bare trees. Also, we are just 4 months (literally to the day, on Monday) past the derecho that left widespread tree damage in our region. There are still broken and weakened limbs in the trees that can come down with another hard blow. Unlike the derecho, this would be a wind event lasting a couple of days, probably not reaching the top speeds of the derecho in the 80-100 mph range, but at least some gusts topping 40 mph are well within the range of reason at this point, and 60 mph gusts are not out of the question, as we sometimes get those with just a simple cold frontal passage. The closer the low center is to us, the stronger the gradient between the low and high pressure to the west, the more wind we’ll get. The second thing to note about the map is the blue shades, dark blue over parts of Southwest Virginia into West Virginia. This represents cold air advection, or how much Arctic air is being pulled around the storm system on its backside. The blue colors here, well below freezing at a mile up, would be cold enough to support snow in our area. The mountains of West Virginia and central/western Pennsylvania stand the best chance at this point to get several inches, even a foot or more, of snowfall from this storm, but if this model were to pan out, we could get some significant snow in our region too — especially west of I-81/I-77, and at higher elevations. Right now, I think some wind-flung snow showers will make it into the New River and Roanoke valleys by Monday and early Tuesday. If it turns out to be more, we would have to be concerned about wet snow collecting on those same leafy tree limbs I mentioned earlier.
Heavy rain would be another potential concern, although for now, the likely track of the storm, both as Hurricane/Tropical Storm Sandy and its subsequent hybrid/extratropical low, would keep the heaviest rain well to our east and northeast. Some heavy rain squalls may rotate to the west as Sandy passes by the Outer Banks late Sunday or early Monday … expect some very high waves out there this weekend. If Sandy were to take a turn northwest much earlier, and crash into South Carolina or the Wilmington, N.C., area, our potential for torrential rain and an even more high-end wind event similar to Hurricane Hazel in 1954 would shoot upward — this is not projected on any forecast models at this time, and appears unlikely based on the atmospheric dynamics.
There is still some chance that a major to historic East Coast storm will not develop. A couple of forecast models have intermittently toyed with an alternate concept, in which Sandy slips just east and heads toward Newfoundland, while some energy in the jet stream trough triggers a secondary area of low pressure in the Eastern Great Lakes, Northeast or East Coast. This would certainly scatter some windy cold and snow for a wide region, but it would not be nearly the intensity of what the European model is showing for late this weekend.
In summary, 7 key points for Southwest Virginia:
(1) Enjoy the warm, sunny weather today through Saturday. It will change fast by late Sunday through Tuesday, because of an Arctic cold front, whether or not the hybrid storm comes to its full fruition.
(2) Anyone with travel plans anywhere in the East early next week, especially toward the coast or anywhere north and east of us, should monitor forecasts closely and strongly consider postponing or cancelling plans if the higher-end possibilities are projected to become reality.
(3) High winds, possibly hurricane force, and coastal flooding may occur along the Eastern Seaboard anywhere from North Carolina to Maine (after first brushing Florida as early as Thursday night), starting to the south over the weekend and extending north through the early to middle part of the coming week.
(4)Some wind gusts topping 40 mph will probably occur in SW Virginia early next week. Wind gusts topping 60 mph are possible, depending on the storm’s strength and track. Tree damage and power outages may result. Be prepared.
(5) Snow is possible as cold air wraps into the storm Monday and Tuesday, with the best chances in higher elevations and west of I-81/I-77 corridors, especially in West Virginia’s mountains. The storm’s path and strength will determine if this is snow showers, like we typically see on northwest winds in winter blowing over the mountains, or more widespread significant snowfall.
(6) Heavy rain squalls may blow into the region as the storm passes to the east, but at this time, the core of heavier rain is expected to stay to our east and northeast.
(7) The likelihood is increasing that a large East Coast storm will develop early next week, but it is not yet a certainty, and its track, timing, strength and effects are details that won’t be hammered out with any reasonable confidence for a few days.