5/13/09 FCST: IA/IL/MO/OK

[Eric Flescher]

thanks for assessment one clarification

Thanks for the assessment about Wed.
what exactly did you mean by "during a brief window before a solid line congeals down the cold front into MO"?

(1) Are you saying that you think things might get active near to Kansas then Illinois - in Missouri, (if you know what mean?
(2) we are two days out so it is hard to know -
(3) good luck
thanks


::

Illinois looks like its definitely in play, sandwiched between the LLJ over IN and the upper level jet/trough over IA. I think the specifics of picking a target are going to depend on the location of the morning convection, which will have to wait until the morning of the event. I concur with Andrew's assessment of the situation. Instability might be greater between Jacksonville and St. Louis where the morning junk has had more time to clear out. Also if there is no prefrontal initation in the warm sector, the cold front might be playable where it intersects an outflow boundary or the quasi warm front of the recovering warm sector. This triple point play might work during a brief window before a solid line congeals down the cold front into MO.

 

[Skip Talbot]

Well, there is going to be strong forcing all down the cold front. The cold front is forecast to drape from IL down through MO, KS, and into OK. I meant that storms are going to be discrete only briefly on the cold front, because the forcing is going to cause a solid line of storms to fire down this front. I'm not sure which areas will light up first, probably the northern end where the shear is greatest. I'm not saying I favor KS over IL. I favor IL mainly because the shear is much better on the northern end of the setup closer to the surface low and LLJ. The cold front is less focused here as well, so the storms won't be forced into a linear mode right away. Of course I also have a location bias. I also am not favoring MO due to a geographic bias against hills and trees. If you are going to play the southern target, I would go all the way down to tail end charlie in OK. Directional and speed shear are much weaker here, however.

 

[Danny Neal]

I just have a couple glaring concerns in my mind....

#1 - What path will the MCS take Tuesday night?
#2 - Where will the MCS lay down an OFB?
#3 - Will the MCS clear out by 1 PM?

The NAM intrigues me. (HERE) - If I am to believe this, we should see an OFB kicked south into C. IL and should be the focal point for perhaps a few tornadoes.

The GFS IMO overdoes the amount of CAPE (pushing 2500+ over most of IL) Although the GFS does have good shear (Sounding) (That sounding is really nice, but in an area the MCS will probably destroy).

All of these factors have complicated WHERE I want to chase not IF I want to. We will see in the coming 48 hours.

 

[David Draun]

I'm actually hoping for a more northern play, like around the I-80 corridor. The hodos look fantastic for supercells throughout the entire warm sector, especially early in the period. Moisture is supposed to scream northward after almost being non-existant on Tuesday. Where this morning MCS sets up is going to be key to where that OFB ends up. I don't like how most of the soundings show a nearly saturated profile up to the EL. Probably convective feedback from the MCS.

I can go as far south as the Springfield area so I am planning on a trip. If I go, I'm targetting areas between 55 and 57 east of Springfield, IL.

 

[Andrew Pritchard]

SFC / 500 crossovers for 4 PM Wednesday.

 

[John Farley]

SFC / 500 crossovers for 4 PM Wednesday.

Well, I hope that timing verifies because if it does, I can still chase and make it home in time for my evening commitment! That is a little faster than the NAM had it earlier, but of course it is still too early to know the exact timing. And as others have said (and as is typical in this area), the specifics will depend in part on the effects of convection the night or early morning before the main event.

 

[Dan Robinson]

Potential target modifier is the organized MCS shown by the GFS (absent on the NAM) tracking across the southern part of the threat area. GFS has it lasting all day through KY. That would be a nice E-W boundary-producer, though a little too far south if the GFS positioning is correct.

 

[Jeremy Den Hartog]

The 'action' may end up being further north and west then I originally was thinking (originally my eyes were set on Springfield, IL as an initial target) due to cloud cover from the overnight Tuesday convection. The latest forecast reasoning from the NWS forecast office (in Lincoln, IL) is hinting at a better chance of clearing further north and west and thus a better chance of destabilization. This is also the area they are looking at for late afternoon development and mention the high chance of supercells at this time as well. My new target is more towards the Galesburg, IL area - but obviously its way to early to lock this down.

In any case, I'm excited My Wife and I managed to get the day off from work so we will definately be out and about

 

[Michael O'Keeffe]

After doing a little bit of research on some of the bigger Illinois outbreaks, such as April 19, 1996. I am very surprised to see that the SPC thinks this will be a mainly linear event. We will have very good directional shear compared to April 19 which had fairly unidirectional winds, however it had a dryline which could have made the difference. Either way it appears we wills see convection well ahead of the front along the warm front or OFB which will likely be where I will setup. I am guessing after dark when the cold front moves into Illinois will a large MCS develop. With that said the threat for an outbreak of supercells appears likely at least before say 9-10pm with a obvious threat for tornadoes given the strong shear. Now all we need is the good destabilization.

 

[Adam Lucio]

I really wish the stupid NAM would stop crapping on the setup so much as far as instability goes. Ive liver here long enough to see these amazing setups just go to waste due to lack of instability.

If we get the instability though we will have a great chase day I think. Im shocked SPC only mentions linear convection. Certainly the forcing along the front does indeed suggest an MCS will develop but all the ingredients are in place for some supercells as well.

Hoping the NAM comes in line with the GFS, then I will be really excited. For now though, its interesting to see some of the plains chasers coming out this way. Hopefully IL can deliver because the terrain, data and roads are awesome in most sections of this state.

 

[Ryan Wichman]

Im shocked SPC only mentions linear convection. Certainly the forcing along the front does indeed suggest an MCS will develop but all the ingredients are in place for some supercells as well.

You have to remember what time this forecast was issued (2:30am this morning) that is still a long way out of the event. Discussing supercells that early in the game can be risky (especially in this part of the country). Especially with the model spread that was still and still is evident. I will be interested to see what the folks at SPC have to say tomorrow morning outside of an obvious wind event.

 

[Dustin Wilcox]

I think the amount of forcing and weak cap has more to do with the storm mode rather than the available/type of shear in this case, tough for supercells to maintain themselves when the whole region blows up. That being said I think there is decent potential for some tornadoes, along that E-W boundary, the NAM is weak with the instability as it wants to have convection over the region all day, likely skewing the instability in a negative manner, hopefully that ongoing convection doesn't verify and a good 3-4 hours of clearing occurs over most of the region. I'm not committing yet, the strong forcing, weak cap and subsequent all day convection, combined with the profile supporting largely HP supercells has me debating if it's worth the trip. But as it is now I am leaning towards chasing, as I think there is a decent shot at a couple tornadoes, and it looks like one of the last ops (other than Maybe Friday) for a while. I'm only 7-8 hours from Effingham (my 18Z NAM target, mainly b/c I love the name) so I can make a last minute call.

EDIT: There's always the OK/KS border region play as well, should I not feel like chasing East...

 

[Benjamin Rock]

I'm targeting the Galesburg to Champaign area for now. As long as the GFS and NAM line up and we get the convection needed that is. Otherwise I may just surf the I-80 corridor. Either way, I will be out and about as well. As it sits, I'm going to see what the newest SPC outlook says at 1am. This may change my target area.Either way,see you all out there!

 

[Chris Allington]

18z runs from tonight look a little worse with slightly less instability over the Northern target across most of IL. The directional shear is still pretty decent across most of Central IL and the speed shear remains about the same. It looks like the clearing doesnt really want to happen until slightly before 18z Wednesday based on the rapid increase in surface temps and resulting instability between 18-00z. However, if the models continue with this downtrend on the instability across the target area I probably wont make the drive, good thing is I can watch it all the way up until tomorrow night though. I like the forecast instability across the Southern target area in SE KS and NC OK but the wind profiles seem to be a bit more uni-directional.

EDIT: 00z NAM looks more unidirectional too, even up near the hint of a surface low in NW IL. Hopefully the models are just suffering some convective feedback issues and overdoing the amount of morning/ day time convection.

 

[Andrew Pritchard]

Unidirectional?

SFC / 500 Crossover

SPI sounding at 0Z

2000 j/kg sfc cape nosing into my "near STL" initiation point as well.