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Morning showers and storms, plus debris clouds from activity to our west, may again cut off any effort for temperatures to climb to 90 today. That may be made up for, though, by humidity in the air as temperatures push into the 80s with any sunshine that breaks through. Showers and storms will be possible throughout the day with heat and humidity and an approaching cold front, but a larger chance exists on Friday when the Storm Prediction Center has put most of Virginia (mainly from Roanoke eastward) in a slight risk of severe weather, even mentioning the potential for rotating storms and a few tornadoes as winds may shift with height as a low pressure system develops along the front.

That will lead into several days of below-normal temperatures. Don't be surprised if a day or two this weekend fails to hit 80 at what is, historically,  the peak of the year's heating cycle.

In its morning forecast discussion, the National Weather Service in Blacksburg notes that surface winds from the east (sweeping in Atlantic moisture) and winds above 10,000 feet from the west may lead to very slow movement of any storms that develop today. The result could be localized very heavy rain ... such as that the weather service reported from a storm in Carroll County overnight, which was over 6 inches in spots. So while many folks may see little or no rain, a few small areas may get creek-flooding rains in a short time. Whether there are any severe storms, with high wind or hail, will depend largely on how warm it gets today. So don't be surprised to hear thunder today or big rain drops pounding on your roof.

Click here to keep an eye on National Weather Service radar today.

It looks like chances of rain are back for many of the next several days, with moisture pushed in from the Atlantic and weak upper-level disturbances from the Ohio Valley the next couple of days, and with the potential of a slow-moving or stalled front into early next week. Right now, Saturday looks like the driest day of the bunch, though getting kinda hot with a high pushing 90.

A low pressure system to our northwest may pull a warm front northward on the Fourth of July. This front may serve to trigger some showers and thunderstorms, and could act as a guide-wire of sorts for any thunderstorm clusters that form in the Ohio Valley. Something Fourth of July festivity planners will want to keep an eye on is whether any of this storminess will arrive in our region by Saturday night about fireworks time. It's a coin flip or lesser chance now ... just keep an eye on things, especially national and regional radar, Saturday.

Sunday looks to be a much better chance of showers and storms (slight risk of severe weather) as a cold front moves into the region and winds, at least temporarily, turn to the southeast to build moisture. But this front will have the net effect of reinforcing the recent mild, dry weather next week, and the familiar recent pattern of high pressure in the south-central U.S. and our region in a northwest flow looks to return.

Disturbances moving through the northwest-to-southeast upper air flow and a weak front moving in from the west may trigger a few storms this afternoon, and the Storm Prediction Center has placed much of our region in a slight risk of severe weather. These disturbances provide some colder air aloft and some increased wind flow that could allow some storms to organize, despite less than optimal moisture. Locations east of the Roanoke Valley in the Piedmont will have  the better chance of stronger storms, as westerly downslope flow may cut off some of the potential nearer the mountains. Still, something to keep an eye on this afternoon on what will otherwise yet another rather pleasant July day.

So far, Southwest Virginia has mostly dodged the potential for powerful thunderstorm clusters to move into the area from the northwest. But the region is under a slight risk of severe weather once again today, for the possibility that new storms could fire in the unstable air mass as disturbances move through and a cold front approaches, with strong winds as the primary threat.

Southwest Virginia is in a slight risk zone for severe weather both today and Saturday. It's a matter of watching each sucessive thunderstorm cluster moving southeastward out of the Upper Midwest and Ohio Valley. The next one to watch is diving through West Virginia now, and might come into all or part of Southwest Virginia by early afternoon.  Gusty winds will be the main severe weather threat ... and there will be the ever-present threat of unwanted locally heavy rainfall. With temperatures possibly challenging 90 and dew points in the 60s to near 70, there is plenty of instability and moisture available to charge storms today.

National Weather Service-Blacksburg radar

Regional and national radar

Although there is a slight risk of severe weather today, it may in fact be a drier day overall today with the bulk of rain and storms both east and west of Southwest Virginia. Friday, during the day, also looks fairly dry for now, with only scattered showers and thunderstorms. But there is growing concern that severe weather organizing in the Ohio Valley on Friday will affect the region Friday night and Saturday, which could mean another shot of widespread heavy rain, too, before cooler and drier air settles in for early next week.

Here's a link to a story in today's Roanoke Times about rising rivers in the area

Wednesday's storms were a little more widespread and organized than Tuesday's. Expect Thursday's storms to, at least potentially, be more widespread and organized than Wednesday's, with perhaps stronger atmospheric wind profiles as more energetic disturbances ride eastward south of a stalled front to our north. Some storms may be severe yet again, with gusty winds and large hail the primary threat again ... though Wednesday's rotating storm in eastern Roanoke County shows that there is always the potential for something a little more unusual if local conditions are right. A widespread tornado/violent storm outbreak does not appear to be likely at all, but some local wind damage or hail dents may occur, with many folks getting a period of torrential rain and some cloud-to-ground lightning.

National Weather Service at Blacksburg

Storm Prediction Center

Click here for a Weather Journal column about why this storm may have developed rotation

Right place, right time. I was watching the storm build east of downtown Roanoke, and noting some rotation in it, even before the tornado warning was issued once National Weather Service Doppler radar began picking up tight rotation within the storm just before 4 p.m. This photo (bigger version here), taken from the roof of the Roanoke Times building, captures the counterclockwise circulation I observed, with the arm of clouds coming in from the left wrapping toward the center of the circulation back behind the Wachoiva tower. Some hail up to an inch in diameter was reported in Vinton, very indicative of a storm with rotation lifting water droplets higher in the atmosphere for a more sustained time.

Here is one clue as to why this storm might have exhibited rotation for a period of time: A midafternoon chart from the Storm Prediction Center shows a small pocket of 40 knots of wind shear up to 8 kilometers high located over the region where the storm developed. We typically look for 40 knots of shear (wind changing speed and direction with height) up to 6 kilometers high as the baseline for likely supercell development.  This storm may not have had rotation long enough to be a supercell, but it certainly started out with a supercelluar-type structure. Another possibility I am wondering about is some kind of atmospheric boundary produced by the storm cluster over central Virginia last night. An outflow of cooler air from previous storms can produce horizontal rotation where it bumps into a different air mass  or a terrain feature (the Blue Ridge?), and that rotation can be pulled into a storm's updraft, producing vertical rotation. That is just conjecture on my part at this point.

Click here and here for additional photos I took of the storm organizing just before the tornado warning was issued.

Ron Bailey of Vinton sent in several photos from the storm as it passed overhead. The lowered cloud structure on pics 6 and 7 definitely has the appearance of a possible wall cloud, or lowering with circulation that has the potential to drop a tornado (though it appears that no tornadoes actually touched down.)

David Gray sent this photo of rotating storm clouds over his backyard in Vinton.

A reader only identified as Kelly sent in this photo from over Cardinal Glass in Vinton.

A small photo of hail accumulation in Vinton from Karenna Glover, who works in marketing at the Roanoke Times.

Today looks a lot like Tuesday ... a slight risk of severe weather is out for Southwest Virginia from the Storm Prediction Center.  Expect storms to develop with daytime heating and terrain features during the day, some of which will become locally severe, a few of which could become a little longer-lasting with somewhat stronger winds aloft with any passing disturbances. Hail and high winds are again the main severe weather concerns, with heavy rain and frequent lightning also likely in the strongest storms.