UPDATE 4:30 PM, 9/8: If you are outdoors Saturday, be prepared for passing showers and storms midday and afternoon
UPDATE 4:30 PM: The severe weather threat has ended west of Lynchburg and Danville as cooler, more stable air has pushed in. As expected, the severe thunderstorm watch has been lifted for Roanoke and nearby localities. There are some showers in the cooler air behind the front, enhanced some by upslope northwest winds similar to what happens with winter snow squalls, but the threat of severe storms and torrential rain is over. END UPDATE
UPDATE 2:20 PM: Severe thunderstorm watch has been issued for Roanoke, Franklin, Botetourt, Patrick, Rockbridge, Bedford counties and eastward until 10 p.m. Expect it to be lifted long before that time, once this afternoon’s immediate severe weather threat pushes east. A somewhat disorganized line of showers and storms continues to move east from West Virginia and far southwest Virginia, while additional showers and storms are forming a broken line east of the Blue Ridge One thing to watch for is whether the eastern line strengthens while the western line weakens — this would be the “Blue Ridge jump” we’ve talked about some recently. Whichever line becomes the primary one, storms will have a greater threat of gusty winds as they enter more instability and greater shear, generally east of the Blue Ridge. Looking more like 3-4 p.m. for showers/storms to arrive in New River/Roanoke valleys, and it likely wont’ be the same experience for everyone, with some getting heavier rain and winds than others. END UPDATE
UPDATE 12:30 PM, 9/8: The Storm Prediction Center notes in a newly issued mesoscale discussion that a severe thunderstorm watch may be issued for the Roanoke and New River valleys eastward as a line of showers/storms in West Virginia advances into greater instability and shear near our region this afternoon. It appears that this line of showers and storms will arrive around 2-3 p.m. in the New River and Roanoke valleys with heavy rains, gusty winds and lightning possible. Farther north, a severe thunderstorm watch has been issued until 10 p.m. for much of northern Virginia, as far south as Charlottesville and Staunton. The greatest atmospheric shear is farther north yet — there has already been a possible tornado reported in Queens, N.Y. END UPDATE
UPDATE 9:45 AM, 9/8: Based on radar and forecast model trends, the front and potential for a squall line appears to be a bit slower. The best chance of showers and storms will be in the 1 p.m. to 5 p.m. timeframe today. A longer period of sunshine will allow for greater daytime heating, which would increase instability and boost the chance for some strong to severe storms, with gusty winds as the major severe threat. Still, activity may not be “widespread or consistent,” as stated in a National Weather Service forecast discussion. The best plan for outdoor activities today: Go forward with them, but keep an eye on radar, be prepared for a period of showers and storms this afternoon, and possible storm-related delays.END UPDATE
Fall is making its first big move against summer, but that doesn’t come without some violence. A massive line of storms Friday evening and overnight has left behind hundreds of reports of wind damage — yes, part or all of it might even qualify as a “derecho” — along with some large hail, flooding and some fatalities in several states to our west. This line will move our way on Saturday, but it’s likely to lose a lot of steam during the cooler morning hours, and also as it encounters the shortening of its updrafts as it crosses the mountains. At some point Saturday, the line is likely to get a new shot of strength over central and eastern Virginia, as it encounters daytime heating. What happens to it in between, as its crossing our area, is subject to some conjecture, as forecast models differ somewhat. It is possible the line will push through Southwest Virginia late Saturday morning or early in the afternoon, with some locally gusty winds possible, before resurging east of the Blue Ridge. It is possible that it may weaken to just a broken line of showers moving through our region. Either way, if you have outdoor activities on Saturday (NRV SkyFest Air Show, Olde Salem Days, and football games at UVa and Virginia Tech come to mind), at least be prepared for passing showers and storms and a possible delay, probably sometime between 10 a.m. and 3 p.m., though we’ll have to monitor radar in the morning to see how the line has progressed. An all-day, wall-to-wall rain is not expected — most forecast maps are pretty meager on the rain amounts, too, in our region. It will move through quickly. The New River and Roanoke Valleys are included in the western edge of the slight risk severe zone (as of shortly after midnight Saturday; click here for latest from Storm Prediction Center), but the much greater risk for severe weather will be to our north and east, where greater daytime heating and/or shearing winds aloft will accompany the storms.
Once the cold front pushes through, a few days of highs in the 70s and lows in the 50s will result. There could very well be 40s in the typically cooler locations, generally west of Roanoke, by Monday and Tuesday mornings.