UPDTE 7 PM: Squall line approaching from WVa, but it’s NOT a derecho; tropical soup stirred up into showers/storms next 3 days
UPDATE 7 PM: Storm line has maintained a little bit better speed than earlier projected, and will be moving through the Roanoke and New River valleys over the next hour. Expect some gusty winds (mostly 40 mph range, perhaps a few stronger ones) and locally heavy rain as it blows through. END UPDATE
UPDATE 5:30 PM: A squall line, bowing to some extent, is approaching our region from West Virginia and may arrive near sunset or shortly thereafter, especially west of I-81. That may sound familiar, but this is a more typical summer squall line and NOT a derecho. There have not been all that many wind damage reports from the line — a cluster in eastern Kentucky – and definitely not enough 75+ wind reports (none at all through 5:30 p.m.0 over more than 200 miles that would put this in the league of “derecho.” That said, some gusty winds will be possible as it blows into parts of western Virginia later, and even numerous 40 mph gusts with localized 60 mph gusts may be enough to loosen some more limbs and knock power out to a few areas. Widespread outages and damage on the scale of June 29 are definitely NOT expected with this squall line — but don’t be surprised to see a severe thunderstorm watch issued later for more of Southwest Virginia (covers region west of I-77 through 11 p.m., ) and probably a few severe thunderstorm warnings — though as of this writing at 5:30 p.m., there is not a single severe thunderstorm warning on the line in West Virginia. Click on Radar / Futurecast in the right margin (and linked here) for the latest look at the progress of the line of storms. END UPDATE
A slow-moving cold front is going to get hung up a little north of us the next 48-72 hours, with some low-pressure waves moving along it. (At left is an inset of Saturday’s weather map, which still shows the front over northern Virginia) Last week, the front got hung up south of us, and the result was that more of the rain and storms occurred in the Carolinas, with some areas near the Virginia-North Carolina line getting some repeated rainy/stormy periods. The atmosphere is thick with moisture, and the front, the low-pressure waves, upper-level disturbances, daytime heating, terrain effects and leftover outflow boundaries from previous day’s storms will continue to redevelop showers and storms over Southwest Virginia and most surrounding regions Thursday, Friday and Saturday. (Don’t rule out seeing some rain overnight, as some remains of the storm cluster in West Virginia may make it southeastward into our region). There’s a good chance everyone will get at least somewhat wet, especially Thursday and Friday, with some pockets of heavy downpours. The Hydrometeorological Prediction Center is calling for 1.50 inch over most of the area over the next 3 days – like I said before, the rain area probably won’t be that smoothed out, but 1-2 inches as an average between the flash-flooding areas and the have-nots (under half an inch) seems reasonable given the humidity, the weather features and the timeframe. Some strong to severe storms with locally damaging winds will be possible each day.
Roanoke hit 95 degrees on Wednesday, making the 12th 95 or higher day of 2012, which puts this year in the top quarter of the last century for number of 95-degree days and makes 2010-11-12 the first time since 1952-53-54 that three consecutive years have had at least a dozen 95-plus days each. We’re probably done with that level of heat for at least the next 5-7 days, as rain and clouds will keep temperatures down into mostly the 80s (maybe some low 90s) Thursday and Friday, and cooler air behind the front over the weekend will push highs back down into the upper 70s/low 80s before heat returns again next week. Humidity is not likely to abate much at all over the next several days, except perhaps for a single day after the front passes — Sunday appears likely to be the coolest, least humid day of the next week.