UPDATE 4 PM: Storm threat on Wednesday worth keeping a close eye upon
UPDATE 4 PM: The part of the tornado watch that affected counties just east and north of Roanoke has been cancelled. We await the storms overnight from the west and southwest. END UPDATE
UPDATE 1:45 PM: The central part of Virginia westward to Alleghany, Rockbridge, Botetourt, Bedford, Franklin and Henry counties (Roanoke/Roanoke County/Salem just barely notched out of it) are under a tornado watch until 8 p.m. This is for the showers/storms currently developing along the Blue Ridge that will encounter strong enough instability and wind shear to intensify through the afternoon as they move northeastward. Quoting the Storm Prediction Center in the discussion linked to the watch: “THE TORNADO THREAT IS NOT PARTICULARLY HIGH…BUT SUFFICIENT LOW LEVEL SHEAR IS PRESENT FOR A RISK OF ISOLATED SPIN UPS IN THE MOST INTENSE SUPERCELLS.” So nothing on the order of the April 16 outbreak is anticipated, but localized tornadic spinups are possible. END UPDATE
As of Tuesday night, the “moderate risk” area for severe weather on Wednesday brushes the far southwest tip of Virginia near Wise — but it covers a wide swath of territory to our west including most of Ohio, Kentucky, and Tennessee. (Click here to see the current Storm Prediction Center outlooks, due to be updated early Wednesday morning.) What is expected to transpire Wednesday is that a large number of storms and storm clusters — some left over from Tuesday’s outbreak, some newly formed during the day — will produce widespread severe weather in the moderate risk zone, including large hail, high winds and scattered tornadoes. By Wednesday evening, these storms will link into a squall line and blow through here Wednesday night with a quick jolt of gusty winds, heavy downpours, and some booming thunder. Winds at the surface are not expected to become as angled to southeast or as strong as they were when tornadoes raked the Carolinas on April 16 — more south to south-southeast — so we probably won’t have the same level of directional shear in the atmosphere we did then. There is enough shear, though, along with strong lift with the advancing front, and definitely warmth and moisture, that we need to keep a close watch on this during the day Wednesday. There may also be some more discrete storms develop ahead of the squall that will have a chance to be acted on even more by the swirling winds aloft. High winds are the major threat with Wednesday’s storms, but large hail is possible, and there probably will be at least a few tornado reports within a couple hundred miles of Roanoke on Wednesday, with a slight chance of some in a 50-mile radius. The front will push through late Wednesday night and early Thursday and return us to more typically springlike temperatures by Thursday and Friday.
April 26, 2011 - 10:44 PM
RSS feed 
Storm Prediction Center Weds AM update for today:
http://www.spc.noaa.gov/products/outlook/day1otlk.html
Moderate risk is to our west and highest risk still to the SW over AL, GA and TN.
Thurs outlook:
http://www.spc.noaa.gov/products/outlook/day2otlk.html
As the front crosses over the mountains, the system will lose some steam as the winds are more southwesterly and not southerly as like during the March 16 event.
Here’s the aviation winds aloft tool that shows really great graphics with winds aloft.
http://aviationweather.gov/adds/winds/
As time goes by, a strong 850 mb low level jet is forecast to develop accross the Apps into our region with 55-70 knot winds at 5000-6000′ above sea level (MSL in aviation lingo) and this just may be the fuel to the fire that we will have to watch for especially east of the Blue Ridge.
Clouds appear to be zipping by from the south at an unusually high speed. Perhaps the fact that they are not very high (my software estimates 1793 ft) increases this illusion. Ground level winds are merely a light breeze.
Raining hard in Sw Roanoke near Tanglewood.
Looks like a line of storms building to the SW of Rke.
Those storms in TN fell apart but a more impressive area moving back into that area.
Not an illusion, Lexingtonian. That’s the shear we’ve been talking about. If surface winds were more east or southeast below the southerly mid-level winds and southwesterly winds higher up, we’d be looking at a lot greater supercell/tornado threat. The shear is sufficient for some higher-end storms today but more likely in clusters or lines than discrete supercells that spawn long-track, destructive tornadoes. Still have to keep a close eye on it in case localized conditions favor something greater.
SPC just out with a new Tornado Watch #233 til 8:00 PM tonight for just east of the Blue Ridge.
http://www.erh.noaa.gov/er/rnk/emer/emer.php
To confirm what Kevin says from above, the winds 3000′ above the surface over Roanoke are out of the south at 27mph and swing more SSW and increase to over 50mph above 5000′ If the winds were more SSE and S, look out east of the BR!
I played an early round of golf this morning at Draper Valley GC in extreme western Pulaski County, and had to dodge a few raindrops here and there. Quite windy, especially for the final 12 holes. Just after I had placed the golf bag back in the trunk and changed out of my golf shoes, they got a very brief downpour. Skies looked threatening throughout the round, but luckily it was mild the entire time, 67 to 70, with high “humdity,” of course. Not like a 15 mph wind with 30% humidity, which would have had a real cooling effect. The “kid” was on fire today through the first 15 holes with the putter and once with the lob wedge (chipped in from off the green on the 9th hole, when I would have been as happy as a pig in mud just to get it within 3 feet). Sank four putts between 10 and 12 feet, which is a month’s worth of putts over 10 feet. I do get real hot with my putter about twice a season, so that will most likely be the last time that happens until at least July
At least twice this morning on The Weather Channel I saw their version of a map of the eastern U.S., showing a truly HUGE — even HUMONGOUS — area that is under the threat of severe weather, stretching from upstate New York to the Gulf of Mexico and west to the states on the western banks of the Miss. River. And as Captain Glen Q has already mentioned, there is a pale white or cream area that includes the southeastern quadrant of TENN., western GA., nearly all of Bamalama, and NE Mississippi. I assume that is a greatly enhanced chance of the nasty “T – word;” Tornados!!! Today appears to this letter carrier who does not know all that much about severe weather (other than snow and ice) like it might be a humongous or at least very big tornado outbreak.
This very moment TWC is showing 4 overlapping areas of tornado (warning?) watch boxes in northern Mississppi!!
Alabama is getting absolutely raked by tornadoes right now. Likely to be some bad destruction scenes out of there (and Mississippi and Tennessee) tonight.