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Parts of the Roanoke Valley are getting inundated as I write this, with slow-moving showers and thunderstorms pouring their guts out, while other parts are missing out on most of it (driving around a bit, I went through both areas). It looks like we are back in the familiar pattern of thick moisture, daily warmth and humidity, and occasiaonl triggering mechanisms that will produce occasional, somewhat scattered but copious downpours through mid-week. Some severe weather is possible each day, but heavy rain appears to be the biggest threat.

Even as I finish typing this, we have gone from very light sprinkles to heavier rain where I am in south Roanoke County.

I'm taking advantage of a  somewhat quieting weather pattern (yes, there will be a few thunderstorms most days, which is typical this time of year) to take a bit of a personal break from the weather blog. I'll be back on if something really big happens, but otherwise, enjoy the early summerlike weather pattern.

After a few more showers and storms overnight and Friday morning, the front to the north is expected to finally slip southward Friday night. This should bring an end to the pattern of repeated storm clusters that we've been in for a few days. While some scattered afternoon heating-type and terrain-related showers and storms are possible through the weekend ... typical summer kind of stuff ... the threat of organized storms and severe weather will dwindle.

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.

This is one of those days you can feel the storm potential outside: It's hot and sticky. The Storm Prediction Center , as of midday, has placed western Virginia in a slight risk of severe weather this afternoon, expecting storms to develop along and near the Blue Ridge with daytime heating. Some storms may tap into a bit stronger winds aloft with passing weak disturbances, as well as some stronger forcing with a cold front sinking southward, and become longer-lived and more severe. Gusty winds and hail are the primary threats today.

There were a few thunderstorms on Monday -- even a severe thunderstorm warning for part of the New River Valley for a short time. There will probably be a few more today, and a few more than that on Wednesday, and probably a few more yet on Thursday. Today's storms will be dependent on daytime heating, terrain features and possibly a weak upper-air disturbance or two, with stronger and more widespread storms into Wednesday and Thursday as a cold front slowly approaches and stronger disturbances move through. Local severe weather is a possibility any of those days, as there may be enough instability to drive a few storms with hail or strong winds.

We might see some scattered showers and thunderstorms on Sunday as moisture begins to return to Southwest Virginia. But in the days ahead, that moisture will continue to build, with daytime heating, our mountainous terrain, and a few disturbances moving through serving as triggers to cause new rounds of showers and thunderstorms. Sogginess appears likely to resume this week ... but maybe another cold front pushing through by next weekend. Would you trade wet weeks for dry weekends?

UPDATE 4:45 PM SATURDAY: I don't typically do anything to promote programming on TV networks, as it's not the purpose of this blog, but it is worth noting that TornadoVideos.net successfully drove its new "Dominator" vehicle inside the same Wyoming tornado that VORTEX2 intercepted, the video of which can be found here. The Dominator is a different vehicle manned by a entirely different group than the Tornado Intercept Vehicle or TIV, though both are covered by the Discovery Channel series "Storm Chasers."  Oh, to have had another week or two in the Plains! END UPDATE

Congratulations are in order for the massive VORTEX2 tornado research team for successfully deploying around a tornado this evening in eastern Wyoming, broadcast live to viewers of The Weather Channel. Of course, those of us on last week's Virginia Tech storm chase wish it could have happened a week ago when we were still in the field, but we have time parameters and have to take whatever weather pattern is there. VORTEX2 also has a time frame that ends in a little more than a week for its 2009 operation, so no doubt a big sigh of relief for those 100-plus scientists who have patiently endured the same low-yield severe weather pattern we did the last couple of weeks. Hopefully this intercept will yield a mine of data about tornado development that will lead to better warnings and saved lives in the future.