What is it?

[Chad Cowan]

My vote is for BSC (big scary cloud)... I can't tell if it's an outflow feature or not. This was the 2nd round of storms that moved through Chicago on 8/4/08 after the tornadic derecho, probably the best lightning display I've ever seen. If you watch the end of the YouTube video I have a series of 12 or so shots to give it some motion. Any ideas?

 

[Matthew Fischer]

Chad,

The two cloud shapes on the right look to be towers to the storms. Cause their are two different bases i see thanks to the black lit in the far distance. Then in the middle between the two you have the visual vault if you want to say that. Then in the back and all the brown is rain i think. Though there was a column in the back, by the two blue topped towers that caught my eye though i can't tell you what that is. I haven't looked at clouds like that since this spring!

 

[Paul Hadfield]

Great job on the video, the last two minutes were awesome! Hope you got some good stills out of that session. I might be off but it just seems the action occurring is that of an embedded meso or perhaps even better, a comma head vortex planted within the line. It may have had rotation but I don't think it was tornadic in the true sense. I make that statement only because these features are so common for our typically outflow dominant late summer MCS's. Still an incredible scene and especially for you against the skyscrapers! How many stories up were you? I got the heebeejeebee's when you panned down to the street lol.

 

[Maggie Kahman]

I like 3:25 with that lightning bolt. That was cool!

 

[Stephen Levine]

What a storm!

Thank you for sharing the picture and the utterly spectacular video of your storm. Congrats to you for getting such breath taking freeze frames of the lightning and cloud silhouettes.

Regarding the scene, my theory is that there were two or three discrete cells that were merging or sharing forces (like a developing MCS). The bluish ones in the distance were probably lit up from lightning in the clouds closer to you.
I noted the movement as shown in the video, and have seen this movement with merging storm cells.

 

[Benjamin Rock]

I have to agree with Stephen.. i think it would be storms merging together. It is an awesome sight to behold! My lady friend works in the loop on the 22nd floor and she shot some serious video from that day as well. Now if i could only get her to post it...

 

[Chip Redmond]

Definitely some very impressive video! The lightning was insane!
I would have to agree that it probably was merging cells. The main strongest cell seems to be off to the right and the other two are coming from the left.
However backbuilding seems to be a possibility or development in the wake of the first storm. The clouds to the right do resemble towers of cumulus firing up.

Chip

 

[Skip Talbot]

Hey Chad,

Your shot looks similar to some structure I saw on May 30 in Springfield this year:

The vaulted region in the center of the image was an occluding RFD cut between twin, training supercells. There was an updraft region and rotation on both sides of the vaulted area. Although the schematics of the storms on June 30 and August 4 were quite different, I suspect something similar is occuring here where there is a clear vault between cells created by a strong downdraft, and a concentrated updraft condensing clouds below the storm's base to form that ominous lowering on the left side.

 

[Paul Hadfield]

Hey Chad,

Your shot looks similar to some structure I saw on May 30 in Springfield this year:

The vaulted region in the center of the image was an occluding RFD cut between twin, training supercells. There was an updraft region and rotation on both sides of the vaulted area. Although the schematics of the storms on June 30 and August 4 were quite different, I suspect something similar is occuring here where there is a clear vault between cells created by a strong downdraft, and a concentrated updraft condensing clouds below the storm's base to form that ominous lowering on the left side.

Cancel that on my earlier reply, this makes way more sense.

 

[Laura Duchesne]

Very cool photo and video, Chad!

I second what others have said. I've seen something similar in Texas last year.

 

[Tracey Rogers]

Those pictures are breathtaking....

 

[Joel Wright]

Nice!

That same day I caught the south end of that bow-echo back here in NW IL before it reached Chicago. I had to let it go since it was moving too damn fast. Anyway, immediately following the storms were a few smaller and elevated storms that were putting out an insane amount of CGs. Interesting since the storms in your post are following the main line as well, although not elevated.

 

[Bob Hartig]

Just wanted to add to the list of thumbs-ups on the video and pics. Very nice, Chad! Awesome lightning and a truly beautiful storm. Thanks for posting.

 

[Chad Cowan]

Thanks all!! It's amazing what 8000+ SBCAPE will do for ya! It's hard to believe they restarted the Cubs game with this on the horizon. I'm going to dredge up some archived radar images tomorrow from this time frame, I don't think I looked at any data for about an hour before and after the images. I'm also going to try to make a hi-res .gif file of the series, anyone know of a decent free program?

Matt- These clouds do look straight from the plains, we definitely don't get enough of this around here. Hope to see your Sox in the Red Line Series!

Paul- It could definitely be a mesovortex. I shot the video from my apartment and the rooftop deck, both on the 15th floor.

Skip- I'm also leaning towards downdraft feature, FFD or RFD I'm not sure. By the way, the analog for this sounding was August 28, 1990... that date mean anything to you?

 

[Adam Lucio]

Chad those are awesome. I tried so hard to get pictures of that second round of storms but they were too distant given my crappy camera. The lightning was almost constant and I kept cursing to Debbie [you met her in the plains] that I wished those storms were during the day because the structure I could see in between the almost constant flashes was incredible.

I remember airmchair chasing those storms too and GR3 had a 2.5" hail marker on it and I was thinking "wow, almost golfballs falling in downtown Chicago...nah"