UPDATE 10AM: A cold front is draped this morning across central Kentucky, with showers and storms ahead of it in West Virginia, eastern Kentucky and the far southwest corner of Virginia. As sunshine builds heating (and therefore atmospheric instability) and moisture from Thursday’s storms evaporates to add to the already thick moisture, ongoing showers and storms may intensify and new storms are expected to develop, some in clusters. Heavy rain, gusty winds and small hail are possible in stronger storms this afternoon and early evening, with a few possibly become severe (localized 58+ mph winds and/or 1-inch hail). A punch of somewhat cooler and subtantially drier will follow the front for Saturday and Sunday. Sunday morning will be the coolest point, with widespread lows in the 50s to low 60s — perhaps some upper 40s at higher elevations and protected valleys that are typically cooler. END UPDATE
UPDATE 11PM: An area of moderate to heavy rain with some embedded storms is poised to move into the Roanoke Valley from the south-southwest in the next 15 to 30 minutes, and it may last an hour or two. A storm with vivid lightning and heavy rain passed through Blacksburg in the last hour, and more heavy rain appears to be spreading into that area from the south. Beware of ponding water on roads and lightning strikes if you’re out and about late this evening or in the wee hours of Friday morning. END UPDATE
A batch of storms with an upper-level disturbance swinging northeastward out of Tennessee and Kentucky is moving into Southwest Virginia this evening, with some heavy rain and a few severe weather reports already noted west of Interstate 77. The storms are losing steam as they move northeastward, but some showers and storms likely move into parts of the New River Valley in the next couple of hours, and Roanoke may yet see some rain from this before it slowly dwindles overnight. Some smaller storms may also continue to develop ahead of the larger rain area. The line of storms up toward Ohio and northern Kentucky marks the cold front that will push into our region Friday, likely firing another round of storms, some of which may be severe. The Storm Prediction Center has Southwest Virginia west of Roanoke in a slight risk of severe weather this evening, and most of Virginia on Friday. Two big keys on just how severe the storms could be for Southwest Virginia are (1) how much sunshine can warm the air, and therefore further destabilize it, through any debris cloudiness we have Friday morning from overnight activity, and (2) what time of day the front arrives. An earlier arrival of the front through a more cloudy atmosphere may limit severe storm potential in Southwest Virginia; the longer the atmosphere can cook in daytime heating Friday before the front arrives will ratchet up our storm threat. I’m a leaning a bit toward this being mainly an east-of-the-Blue Ridge severe weather threat for Friday, but enough ingredients — especially thick moisture and a strong source of atmospheric lift with the front — are in place that the Roanoke and New River valleys westward should keep an eye to the sky for the possibility of strong to severe storms Friday, perhaps into Friday evening. Localized damaging winds will be the main severe weather threat, with also some threat of quarter-sized hail. An areawide derecho-type event is not expected, nor is a high-end tornado threat, with the best wind dynamics that could give storms a spin expected to stay well north of us. Heavy, briefly flooding rain may also occur in some storms that are slow movers, particularly those that may develop out ahead of whatever squall line accompanies the front.
The front will bring the coolest shot of air we’ve seen since June, with many lows in the 50s by Sunday morning. Roanoke has not had a low below 64 since June 28, and Sunday’s low behind the front is expected to be close to 60. Normal summertime temperatures recover by early next week, but extreme heat above 95 is nowhere on the horizon. I think we’re done with triple-digit stuff this summer in the Roanoke area.
Meanwhile, with Tropical Storm Ernesto now ashore in Mexico, the National Hurricane Center is tracking three potential tropical systems in the Atlantic – the remnants of Florence, Tropical Depression 7 and a new wave emerging from Africa. All are days away from any potential impact on the U.S. Tropical Depression 7 may well become Tropical Storm Gordon in the next day or two and track into the Caribbean, similar to Ernesto.