Persistent “in-situ” wedge of cooler air will further delay Roanoke’s first 90-degree high of 2012
Here’s a surprising little statistic that seems to swim upstream against the fact that the March-April-May period was the warmest spring on record for Roanoke — it still has not hit 90 degrees on any single day (high was 89 of 4 different days). And it won’t get close to that today, because of what is known as an “in-situ” wedge of cooler air. The wedge is created by persistent showery weather creating a pool of cooler air east of the spine of the Applaachians, rather then more familiar wedge pushed in by high pressure from the northeast (what we would call “cold-air damming” in winter). Most areas won’t get out of the 60s today.
So, whenever it finally makes 90 (possibly the weekend), it will be Roanoke’s latest date for its 1st 90-degree high since at least 2004 (June 11) and if it delays much later, since 2003 (June 20).
I’m back home and recovering from an unusual and intense Virginia Tech storm chase trip. More on that later.
June 6, 2012 - 9:26 AM
RSS feed 
The wedge is definitely in full force…I had to walk around a lot this morning for work, and I got rather cold actually, in 55 degree air with drizzle and a sometimes rather noticeable easterly breeze. 6 days into meteorological summer and 2 weeks before astrological summer and there’s a wind chill…gotta love life in the mountains!
Kevin…a follow up from last Friday’s storms around 5:30pm…there was some isolated straight line wind damage to Advance Auto Part’s Distribution Center here at Blue Hills Drive…insulation from roof damage was blown across the street and a 53′ empty trailer was knocked over.
Has there been any additional discussion about the photo from Fincastle?
No discernible ground evidence of a tornado has been found near the site of the Fincastle photo so it will likely remain unconfirmed — neither confirmed nor denied as a tornado.
Botetourt View reporter Cathy Benson, who took the photo, has written a little bit about her frustrations regarding the identification process (plus you can see the photo again).
http://blogs.roanoke.com/botetourtview/2012/06/terrific-tuesday-weather-or-weather-not-it-is-my-dead-horse-photo/
I would have to say that one significant possibility is that it was low-level “scud” clouds being pulled into an updraft. The feature in the photograph has more of a lumpy appearance rather than being a smooth-sided funnel like would normally develop in a the upward rotating vortex of a tornado.
Here are a couple of past examples of that I posted on Weather Journal.
http://blogs.roanoke.com/weatherjournal/2009/08/so-was-this-a-tornado/
http://blogs.roanoke.com/weatherjournal/2009/08/another-non-tornado-but-some-heavy-rains-and-gusty-winds/
But it is also possible there was a poorly defined circulation within the tube of clouds.
Without having personally observed it or closely followed the radar in that specific area at the time, I reserve judgment.
When I first saw it, not having video to depict rotation, my thought was a scud cloud based on the Skywarn training I’ve had.
I reckon a sit-in wedge is as gooda answer as any, cause it has sit-in over da Knob for 2 days. Callit what you like, but I’ll call it nasty weather fer June 5th and 6th.
Today’s high temp at RRA was somewhere in the mid/upper 60s …. wunderground has it at 67*. That would be 14 degrees lower than Roanoke’s normal high temp of 81. Tomorrow will be close to the normal high, and the weekend looks to be above normal.
Regarding Cathy Benson’s dead horse… if the reporter saw it come out of a cloud down to earth, wouldn’t that imply the genesis of a tornado, rather than merely a collection of scud clouds?
In the absence of video, perhaps she could put together a chronological array of pictures that might explain how the cloud came together.
Kevin…Is there a way to view historical radar images?
Ive never seen “in-situ” used in
a weather discussion.
I suppose its the same as localized phenomenon.
,,but I suppose in-situ would especially apply
without rain..(since the rain usually comes in from outside
the area) where u are talking about cooler air off the ridges
pooling in the valley with no wind to move it out.
In-situ usually means staying in original place…Ive always thought
of weather as having some kind of movement always.
…I was certainly “in-situ” (nailed to my desk) last night.
slow moving low and thunder whacked us in DFW…many many many flight diversions…many many flights routed on unusually long plans exceeding the fuel capacity of those flights as well.
I just did some research on scud clouds, and watched some on youtube, because I didn’t fully understand what they were. Some of the videos showed slight rotation of scuds (due to coriolis effect I assume). Could a particularly intense scud cloud become a tornado..or are the physics of the two completely different?
I’m a day old on this post — hit some homefront delays in posting new.
“Scud clouds” — the kind of random small pieces of cloud in the lower atmosphere — actually do often get drawn up into the updrafts of a storm prior to tornado formation, often forming the wall cloud. Rising scud is a common thing to look for in a supercell — but that’s not the only time it occurs.
Tornado formation is often kind of counterintuitive. A tornado is an updraft, not a downdraft, so in a sense it forms upward. But the condensation funnel usually has the appearance of developing downward from cloud to ground, and indeed, a broad updraft can tighten downward into a tornado. Some tornadoes are first seen as a whirl on the ground beneath a wall cloud or storm base with no funnel at all in between (and some remain “invisible” throughout their life). Many tornadoes have a funnel that doesn’t touch the ground but does have a debris whirl on the ground underneath.
A cloud tube developing downward from a storm to ground would not necessarily signal a tornado. It would be just as easy for cloud material to get caught in a downdraft or to develop downward along some kind of non-rotating moisture condensation axis as it would for scud clouds to be pulled upward into non-rotating updraft.
Cathy Benson did post a progression of photos, linked at http://blogs.roanoke.com/botetourtview/2012/06/was-it-a-tornado/, but it doesn’t really capture the genesis stage.
The National Climatic Data Center does have a database of old radar data. It might not be conclusive for a number of reasons: a brief, weak rotation may not be picked up, there may not have been enough precipitation at the time to get spun around for the Doppler radar to pick up moving particles, and terrain could have blocked it. May be worth a look at some point, though.
This “was it/was it not” tornado situation with no resolution is nothing new. We actually saw a somewhat similar event in Oklahoma a week ago, a cone with a debris whirl underneath an obvious supercell wall cloud, that may never be confirmed because there was apparently no ground evidence. It appears to have just spun up dust. There’s a chance it wasn’t a tornado, but we and some other chasers/spotters on the scene feel strongly that the overall evidence of the total storm situation points to it very likely being one. One scientific estimate is that 2/3 of all tornadoes that touch down in the U.S. go unreported or unconfirmed each year.
If it wasn’t a tornado, it would do very little to change the overall storm experience we had that day.
I downloaded the Level 3 base reflectivity and relative velocity data from the NCDC. I’ve made .avi files of these. Unfortunately, the area in question appears to fall squarely within the radar shadow in the western part of Botetourt County, so the relative velocities barely show up at all. Would have been very difficult to detect any rotation or issue any doppler-indicated tornado warnings in this situation.
Base reflectivity:
Relative velocities:
I gotta figure out how to post links on here. Trying again…
Base reflectivity
Relative velocities
I was afraid it might fall in that shadow. (Radar beam from Floyd County ridgetop blocked by Poor Mountain). Thanks for checking.