3/25/07 NOW: IA/WI/MN/IL

[rdale]

Haven't really been following the event, but the 00Z GRB sounding certainly looks supportive of tornadic supercells to me. 150mb deep BL moisture

Not much moisture though, and LCL's of 3500ft not a very good sign either in my book... I can see some minor hail threat, but I still don't understand why so many think this is a good tornado environment.

Let me ask the question this way - if you just sat down without seeing the MDT risk earlier, and without knowing SPC issued a Tor Box, would you be excited about tornadoes? Doubt it.

 

[Brett Adair]

I agree with Rob. Seems to me that the CAPE is rather 'skinny' on the GRB sounding also, and it never really begins to fatten up (still not much) until about 830mb. This is due to the lower dewpoints which in turn leads to much higher LCL's as RDale points out above. Seems to me that the lower level shear may be a tad too strong for the updraft to develop and accelerate within this CAPE environment. Had the higher level of shear been just above this CAPE axis....that may have been different. LCL's of 3.5 kFT still don't excite me all that much. SPC has sense downgraded to SLGT and that is a very good call.

 

[afischer]

Not much moisture though, and LCL's of 3500ft not a very good sign either in my book... I can see some minor hail threat, but I still don't understand why so many think this is a good tornado environment.

Let me ask the question this way - if you just sat down without seeing the MDT risk earlier, and without knowing SPC issued a Tor Box, would you be excited about tornadoes? Doubt it.

If by moisture you are referring to boundary layer moisture... 100mb mean layer dewpoints around 11-12C in Wisconsin in late March are not exactly anything to sneeze at. The observed LCL heights of 1100m or 3500 feet are perfectly sufficient for warm/bouyant RFDs.

I wasn't questioning the warning mets or SPC or anything; I was simply trying to add some reality to the mix via posting an observed sounding representative of the near-storm environment.

 

[Mark Sefried]

Not much moisture though, and LCL's of 3500ft not a very good sign either in my book... I can see some minor hail threat, but I still don't understand why so many think this is a good tornado environment.

Your correct as it is not a good tornado environment. However it is sufficent enough. Not for wedges or anything like that but for tornadoes yes.

 

[Brett Adair]

Here's a good refresher from Jon Davies on MLLCL heights & tornadic supercell potential. http://members.cox.net/jondavies1/tornado_fcsting/attributes_tbl_explain.gif

No need for that at all....especially if your better shear is BELOW your better CAPE. In other words, the parcel gets more sheared I believe before it can accelerate upward. Slight capping inversions can always be pesky where no distinct boundary is present also. Therefore, the main 'trigger' can sometimes be convective temp and that wasn't really reached either. Looks like the storms are dying ahead of the main band of vorticity/storms associated with the shortwave/upper level system.

 

[rdale]

However it is sufficent enough. Not for wedges or anything like that but for tornadoes yes.

Well, I think I've made it clear that I strongly disagree

How you can sit fresh and look at what's happening and say we're going to get tornadoes tonight is hard for me to grasp...

 

[Brandon Sullivan]

Note: No Offense to anyone.. And I am not exposed to the elements.. But I think I am agreeing with Rdale.. I think the tornado threat is dwindling as well.. A cooling boundary layer is going to calm things down.. CAPE is on the decrease, LCL's are below the LFC's, and SB LI's are slowing down.. Maybe still see some hail.. But things are about over in my opinion. Glad I stayed home..

 

[David Drummond]

All right that is enough. Any further posts here that are not NOW posts regarding events yesterday will be issued a 3 day ban!

Just got home from a 400 mile chase and I can even delete them as fast as you guys are posting. Some infractions have already been issued, lets not have any more.

EDIT: In fact since that day is over with I am locking the NOW thread.