5/31/06 DISC: IN / IL

[tom hanlon]

I more or less slept through todays events that had tornadoes within 300 miles of home. I feel like I should have at least been paying attention.

What happened today? How did I miss it ?

These East of the Mississippi events seem to be slightly more fickle then the great plains systems. So often cloud cover or too much moisture or linear storms seem to ruin what might otherwise be a tornadic day. Of course these other events keep you guessing about not so awesome setups that turn out a tornado or 4.


What combinations came together today? Why was it not broadly expected? SPC did not seem concerned. Stormtrack did not seem concerned.


What I did see forecasted was pulse storms of slight to moderate intensity but a lack of shear to support organized or long lived storms. What changed ? The heating was indeed intense, did we just get mega-cape and with mega-cape all things are possible ? Did we get an outflow boundary from a previous system that introduced some spin into the equation ? Did the upper or low level windflow pattern shift to allow for some shear at the last minute ?

Just curious if anyone has any opinions on today and could help me learn to be more prepared for the next surprise. I am not questioning the SPC or anyones forecasting ability, I know this stuff is unpredictable. I however failed to watch the setup at all so any links to archived forecasts or model output would be a great help. What did yesterday look like that allowed today to happen ?

Rereading the day one Convective outlook from the SPC I see that a MCV was involved. Truly difficult forecast for sure and likely last minute in nature since it depends on the last days or mornings activity.


--
Tom Hanlon

 

[Jason Hetzel]

I easily asked my own self all the same things for today's events that took place. 2 times here in Michigan in Saginaw County there were 2 official tornado warned cells. Both were VERY low topped supercell structured storms and the first initial storm had confirmed reports of a rotating wall cloud over Saginaw. Just prior to this i did notice on the SPC Mesoanalysis page there was a small pocket of effective bulk shear in the 15-20 knot range over that area. Moderate instability was also in place with sbcapes over 2000 J/Kg and a boundary of some sort which im not too sure what it was (probably a lake breeze front) but was clearly evident on reflectivity scans. My personal guess is that becuase both of these cells were very isolated to the north, and in an open area they both fired along that mysterious boundary and used what little effective shear was in place to get their acts together. I to however am wondering if anybody else has anything to comment on this odd turn of events for today.

 

[rdale]

There were plenty of pics on WISH-TV (Indy) news last night - they were all "spout-ish" looking. Everything seemed to form right on the periphery of the 700mb dry punch. I did not see the first Saginaw Co cell, but I did see the second (visually and radar based) and was concerned that as it approached the outflow from #1 it might start to spin. All rotation was very marginal on radar.

Interesting is IWX had some sort of comm problem so their first SVR didn't go out for 40+ minutes and the TOR was delayed as well, then they REALLY screwed up VTEC codes by reissuing wrong / canceling wrong / etc. In any case spotters apparently saw up to a dozen spinups but never contacted NWS with that info, it apparently was only used within the counties to sound their sirens (unless it's related to IWX's comm issue.) Not until the cells finally started to die did reports come in.

If anything was more than F0 I'd be surprised.

 

[J West]

We had a similar situation on Tuedsay here in WI...there were a bunch of popcorn cells that fired all over WI and IL, seemingly none worth mentioning until a rogue cell in northern WI began to rotate and had a wall cloud with funnel viewed by spotters.

Today is another one...all the local offices still have strong T-storm wording in the HWO, but the SPC revoked our slight risk or general T-storm outlook for the day. I've yet to look at data, but if there is a mystery boundary hiding somewhere then the day could turn around very quickly.

 

[Terrence Cook]

I live just 50mi south of the tornadoes that hit Benton and White county Indiana. I watched the cell explode only 10 mi from my property. It blew up along the southern edge of CAPE in excess of 2,000 j/kg and was the only cell that moved quickly (20-25mph) to the north east while all other storms moved 5-10mi or were nearly stationary. I got a good look at the cell with swiftwx and it showed a nicely organized couplet and a typical looking cell on radar. The website below are the only pics i know of. This is the first time I can recall a "Tornadic Pulse storm". Earlier in the day SPC had a 2% tornado area, but removed it around noon.

http://wlfi.com/dsp_story.cfm?storyid=43145

Reports of tornadoes from Danville to Champaign, Illinois occured at the same time as the Indiana cell.

 

[Ed Boik]

by the time any storms made it near my area, they were an even more disorganized mess. I can see how inexperienced spotters/law enforcment could have mistaken the numerous tube-like scud and apparent "motion" for rotation and funnels.

 

[rdale]

Those pictures are not scud or tube-like, those are real ;>

 

[Chris Geelhart]

Reports of tornadoes from Danville to Champaign, Illinois occured at the same time as the Indiana cell.
[/b]

One of the tornadoes was even observed by the personnel at the Champaign airport:

KCMI 311953Z 13019G22KT 10SM TS BKN042 BKN050 OVC090 23/20 A3008 RMK TORNADO B32 TORNADO E37 AO2 RAB39E50 SLP182 LTGICCG TS S MOV NE P0000 T02280200
KCMI 311938Z 11013KT 10SM TS OVC046 24/19 A3007 RMK TORNADO B32 TORNADO E37 AO2
KCMI 311934Z COR 09010KT 10SM +FC TS OVC046 25/19 A3007 RMK TORNADO B32 AO2 TONADO SW MOV E
KCMI 311853Z 27010G15KT 240V320 10SM TS SCT048 BKN060 29/19 A3008 RMK AO2 TSB37 SLP178 OCNL LTGCG TS SE MOV N T02940189[/b]

The pictures we saw on the news were of a landspout.

Chris G.

 

[Ed Boik]

Those pictures are not scud or tube-like, those are real ;>
[/b]

I wasn't saying tornados didn't happen, I was just speaking of what I witnessed in Central Illinois.

 

[tom hanlon]

I blame yesterdays activity on the MCV that was discussed in the SPC day one early on.

Anyone know of any documents on how to chase such a hard to find vortex.



I find the following discussion online. HERE

Mesoscale Convective Vortices

MCVs are not often diagnosed since they are often hidden by the upper-level clouds of the MCS. Also, not all MCSs form MCVs since the scale and duration of the latent heating and the character of the synoptic or mesoscale environment (e.g., shear, vorticity, and divergence) control whether an MCV is generated.

On many occasions an MCV that survives their parent MCS may later spawn new convection depending upon the large scale environment in which they move. Bosart and Sanders (1981, JAS) tracked the convection that led to the Johnstown, PA flood (19-20 July 1977) to a mid-level cyclonic circulation that developed 96 hours earlier!

Thus, MCVs can be important features to follow for possible severe weather or heavy rain.


Does anyone agree that this is what may have happened on 5/31/06 ? Do any professional meteorologists care to add there two cents and perhaps put this in terms that a "hobby" meteorologist might understand? Does anyone imagine that such an event would be chaseable in terms of predicting stronger activity in a 4 hour advanced time frame ?

Looking at the radar and if you lived close you could see that these storms found something to keep them going and get them rotating. How could you see it on say the SPC mesoanalysis page ? An MCV seems to be a high level feature. Is there enough upper air data to get a good picture of what happened ? Where are the sounding stations in IN/IL ?

Judging from this short discussion on MCV's it seems like they form in exactly the type of environment where they are needed. A low shear environment that is likely going to only produce pulse severe storms sees some convection early in the day or late the evening before. The MCS of the night before creates an upper level vortex due to all the convection and the latent heat sent upward from the convection. This vortex although hard to detect is capable of providing the next round of what would otherwhise be shear-starved storms with the spin that they need to get organized and become severe.

Certainly an interesting topic, perhaps best moved to Weather and Chasing if it becomes a general MCV discussion if it stays centered around 5/31/06 events then it should stay here I suppose.

--
Tom Hanlon

 

[rdale]

I missed their MCV discussion - but I don't see how an MCV would have caused something like this. As mentioned above, if you watch the 700mb dry punch, that's exactly where these storms formed. Even the rotating ones in Saginaw Co MI were on the leading edge of that punch, so I have to believe that was a big cause.

As for predciting these type of storms in 4 hours in advance (or even 4 minutes) I'd say - no way. In such a weakly forced environment there are no telltale clues to indicate tornadic potential. Clearly these operate on a different scale that "real" supercells, but nobody studies them intensely (because they really aren't a big deal 99 times out of 100) so I don't know that your questions can be answered.

But again I did not see any evidence of a MCV. There are no soundings in IN, central IL is the closest.

 

[mikegeukes]

BRIEF F0 TORNADO AND NUMEROUS WEAK GUSTNADOES
CONFIRMED IN WHITE COUNTY INDIANA...
http://www.crh.noaa.gov/iwx/?n=whitecountymay312006f0

Mike