Chicago Dodged a HUGE bullet

[Danny Neal]

I was surfing youtube like usual and now the KLOT has confirmed a tornado on sept 22nd on the northside i went looking for a video and i found two. I have never seen a storm like this in Chicago, i found 2 videos from Loyola Campus as the LARGE wall cloud with violent rotation was seen passing over and eventually puts down a tube over lake michigan....... http://www.youtube.com/watch?v=fhUST6b6qNg thats is the first video watch as the RFD blasts the campus with 60-70 mph gusts and this is the second video showing the tube over the lake http://www.youtube.com/watch?v=KFVgNAuIGOY&NR

where was i during all this, 300 miles to the south in jacksonville....go figure, this tornado was an F-0 as it touched down on the beach and moved over the lake.......if this decided to produce just 5 miles further inland we could be looking at some serious wreckage especially during rush hour

 

[David Draun]

Yes, I agree. The atmosphere was more than favorable for strong tornadoes that day. Wind shear along the secondary warmfront was insane, along with some effective, nearly uncontaminated inflow from the SSE/SE. I was watching plain old TCu rotate! I think the lack of other boundaries (i.e. outflow boundaries and such) prevented the storms from producing tornadoes. I observed plenty of upward motion and circulations on the storms I chased that day. Also the LCL's were a ground-kissing 700m in some areas. I was under a flanking line near the end of the event, and it seemed I could almost reach up and touch the cloud bases! Of course that is a slight exaggeration, but you get the idea. If there were some more boundaries for the storms to root on, there could have been some serious consequences. Chicago is not totally safe from tornadoes like some believe. It's not the lake, or the tall buildings that could prevent them. Chicago has been hit before (in the 70's) and it will likely be hit again. It is just a matter of time.

 

[rdale]

"or the tall buildings that could prevent them."

While I agree Chicago is not immune from tornadoes, I'd have to believe that the buildings / development / etc. might help keep some of the smaller ones from forming...

 

[Andrew Herron]

Could the heat given off by the city also affect a storm's ability to produce a tornado?

 

[David Draun]

I guess if the heat island was strong enough, the dewpoint depression would increase, raising the LCL. But will the heat island increase temperatures enough to make a difference?

 

[rdale]

I don't see what connection heat would have on tornado reduction...

 

[Danny Neal]

i would think heat from the city would prehaps increase the strength of the storm for the fact the inflow would be sucking in all that warm air rather than the cooler air off the lake

 

[Tony Lyza]

I guess if the heat island was strong enough, the dewpoint depression would increase, raising the LCL. But will the heat island increase temperatures enough to make a difference?

Applying the same logic, combustion would also lead to a nearly equalizing rise in water vapor, minimizing any negligible effect.

 

[Tony Lyza]

I don't see what connection heat would have on tornado reduction...

Skilling has frequently mentioned in his "Ask Tom" segments on TV and in person that Fujita theorized that Urban Heat Island Effect MIGHT reduce the intensity by one F-scale level and make it more difficult for small tornadoes to form, but I know of no concrete evidence of this. Of more effect, IMO, would be a lake breeze, which can enhance vorticity in storms moving along it (like 7/17 of this year), but could force storms that move into it to become slightly elevated.

 

[rdale]

i would think heat from the city would prehaps increase the strength of the storm for the fact the inflow would be sucking in all that warm air rather than the cooler air off the lake

Assuming a storm is approaching Chicago from the west, it doesn't 'suck' lake-cooled air until it passes over the lake. It doesn't even suck in Chicago-warmed air until it passes over Chicago. Remember "generic" supercell thunderstorms get their inflow from the southeast quadrant.

 

[Danny Neal]

how far can a storms inflow band stretch? if a storm is moving like this one did from the west side of chicago, northeast? i want to get a better understanding why this storm didnt fizzle out or become elevated like 90% of all the storms do when they reach the lake zone, maybe that day all the dynamics were in place for a supercell well actually 3 of them training in the same area......seemed to me like the dynamics were more suitable further south, was there a boundary this storm rooted itself on? in the video it looks VIOLENT like something you would see on a march 12th or may 3rd well at least around here you never see violent rotation like that, it actually reminds me just by looks of the nashville storm of 1998

 

[Jim Tang]

I think that the water-cooled L. MI and the Urban Heat Island Effect-warmed Chicago metropolitan area may actually serve to provide a small scale boundary that sits right at the Chicago lakefront. This might provide enough vorticity to spark tornadogenesis in supercell thunderstorms that otherwise would not have produced.

 

[Tony Lyza]

I think that the water-cooled L. MI and the Urban Heat Island Effect-warmed Chicago metropolitan area may actually serve to provide a small scale boundary that sits right at the Chicago lakefront. This might provide enough vorticity to spark tornadogenesis in supercell thunderstorms that otherwise would not have produced.

That's essentially the lake breeze effect. I saw it on 7/17/03. It did not cause tornadogenesis, but it did take a strong single cell storm and caused it to explode into a huge HP-supercell with 90+MPH winds and tennis-ball-sized hail.

 

[Danny Neal]

that might have something to do with it, even monday as the line from wisconsin moved south when it got toward the waukegan area, nws issued a tornado warning for strong rotation detected in the thunderstorm but then 15 mins later it had moved over the lake, basically your going to get a rotating thunderstorm or your going to get a rain shower when it hits that lake breeze, more often than not the storm loses severe characteristics when it approaches at least from my experience, but more and more ive noticed theyve maintained strength or even strengthened especiall from 03 on, i wonder the atmosphere a storm has to deal with for it to become rooted on the boundary and why others dont.....i guess thats why weather is mysterious

 

[David Draun]

Supercells on May 10, 2003 in the Chicago area were moving NE into a lake cooled environment. The area had been held in the upper 60's and lower 70's as far inland as Dekalb or so. Outlying areas were able to warm into the upper 70's or lower 80's. There was not much weakening in the storms that approached that evening towards 11pm. I remember my area being tornado-warned at 11:30pm for strong rotation and a violently rotating wall cloud confirmed by spotters.

Also I've heard something about the August 28, 1990 storm being influnenced by a lake boundary, I don't remember exactly where though.