04/08/08 FCST: IL / MO / AR / TX

[Scott Weberpal]

It appears that Eastern Missouri into Central Illinois should be, at very least, maginally primed for supercells (conditionally tornadic) Tuesday.

Surface through H7 kinematics look great, but relatively weak winds at H5 per 12z WRF worry me. Looks like the main H5 energy is hanging back in Iowa and could mean HP mushballs in IL Tuesday afternoon. I'm hoping tonight's run is a little more progressive with the upper trof.

 

[Skip Talbot]

Instability looks like it could be real a problem for this setup, as the 0z wrf run has even further backed off the meager instability the 12z run showed. If we can get some more daytime heating though, the shear will definitely support supercells.

Right now I'm looking at the warm front/cold front triple point right under the low pressure center. The 850 vertical velocities are spiking here, indicating that the dynamics of this system may overcome the lack of instability. There is a narrow tongue of instability forecast right along the I-55 corridor from St. Louis up into central IL. If we can get an updraft in this area, even low topped, the 1km SRH's of 300+ might be enough to get us some supercell play.

 

[Mike Hollingshead]

A FUN HODO in central IL for this day for any that haven't seen it. I should skip Mon and chase this one since it would be closer. If there manages to be instability, could be a little nuts.

 

[Chris Hovanic]

Having to work during the possible big day on Monday, I've also got my eye on Tuesday...

The 0z NAM suggests an interesting high shear/low CAPE environment in place across Western Illinois on Tuesday afternoon. An inspection of the 21z Tuesday forecast sounding at K3LF (Litchfield, IL) suggests a highly sheared low-level wind profile with 0-1km SRH values ~350m2/s2. LCL heights are < 1000m as well as surface temps remain rather cool.

Progged surface based CAPEs are only ~ 600 J/Kg, however 180 J/Kg of this is contained of this CAPE is located in the first 3km of the sounding, co-located within the area of strong low-level shear.

Now I'm not certain what the exact synoptic setup for the April 20, 2004 event was, but the large amount of low-level CAPE in an overall low CAPE environment is similar to that event... see Jon Davies presentation on this:

http://members.cox.net/jondavies3/042004ilin/042004ilin.htm

Another interesting note...the forecasted hodograph at 21z for Litchfield shows the 'critical angle' between the low-level storm-relative inflow vector and the 0-0.5km shear vector as being nearly 90 degrees, which would support tornadic potential...

See the excellent presentation by David Guiliano and John Estherheld on this subject. (http://americium.gcn.ou.edu/presentation.ppt)

Caveats with this event will obviously be the amount of instability available...as elevated morning convection could throw a wrench into an already weakly unstable environment.

We'll see!

 

[Eric Graham]

I'm liking Tuesday's setup even if its not the best. Temps are frcst in the mid to upper 60s and in some runs I've noticed the jet stream is right on top of Illinois and here in IN. I'm planning to head out after class into central ILL and then follow storms back into my home state. Hoping for a descent show.

 

[Jarrod Cook]

Definitely an interesting setup for central IL. The potential is there for supercells and tornadoes given the insane shear. Hopefully this isn't going to be another waste of good shear due to lack of instability. However, with shear parameters this good, it'd be bad to ignore the setup. Initially, anywhere from the I-74 to I-72 corridor looks good, especially from Peoria to Bloomington along the warm front and east of the surface low.

 

[Andrew Pritchard]

This is all based on last night's model run so there's probably no point in posting since I'll likely just wish I could eat my words when the 12z models show so major change.

Either way, based on the 0Z run, it's hard to decide between two target areas. The first being the obvious warm front in central Illinois. The second being a little further south where better instability, and still sufficient shear may exist in southern Illinois. I think at this point the better option is going to be the warm front, right ahead of the surface low which based on last night's models would be right around Springfield. It looks as if clearing could be at a premium tomorrow so I wouldn't place all my money on getting better instability for the southern target. I think at this point, we should have plenty of moisture and just enough heating that the strong dynamics associated with the system, and the strongly defined warm front should be enough to initiate deep surface convection. Any deep convection that can develop should quickly become supercellular with the insane shear in place. As Weberpal noted, I'd like to see a small increase in the H5 winds, but H7 and down are phenomenal.

At this point, I'd love some more instability, but I think the dynamics of the system should be enough to kick off a few supercells across central Illinois. I think we could see a few tornadoes along the I-72 corridor through the afternoon. I'll probably wish I could take it all back once the new run comes in in about an hour or so.

EDIT: Not a lot of huge changes on the morning run. I'll go over things more indepth at a later time, but at this point I'd still consider Springfield a good general target if you believe the WRF. Might need to be there early in the day. Instability is slightly improved from last night. While only a tiny bit, it's better than going the other way at all.

 

[Brandon Sullivan]

Just flipping through some 12z Data... As someone else said, I don't want to see this awesome Shear Setup get wasted by no CAPE.

The NAM takes the low over Central IL.. I will probably play the warm front, and look for some supercells that go can up to the N of the front. I see SPC has draped a 30% over IL and I will target in that area..

Maybe 00z could shift it a little NW? Cmon Weather Gods..

 

[Jim Hunt]

I am not particularly good at forecasting severe weather as many are on here but believe the parameters for discrete supercells ahead of any squall line will be in central IL. While the moisture will be better in southern IL, I think there could be some clouds which may prohibit the best heating.

Tomorrow will be my first chase and I will do it solo as well. (I have done lots of local spotting for Skywarn.) I plan to target Bloomington/Normal, IL around 1 PM and will evaluate data and decide if I stay or need to move south (or north) from there.

Edit Tuesday Morning: I have decided to not head to Bloomington/Normal, IL. Things look much more questionable now. I will evaluate around noon on where to go...

 

[Mike Hollingshead]

The less that happens tonight, the more I like tomorrow in western IL. One has to love the shear ahead of that surface low, with strong low level jet out of the south and wsw 500mb winds. Shouldn't need real great dews with -17c at 500mb prog'd over the region. Tonight really needs to stay fairly dry. If it does, I'll likely head out early for somewhere se of the Quad Cities.

 

[Scott Weberpal]

Tonights RH progs keep much of Central and Eastern Illinois "cloud-free" through 18z, and I'd be more than happy to see upper 60-near 70 sfc temps tomorrow. I would have thought moisture would be quite shallow tomorrow, but mixing ratios appear to be fairly decent for an early April event this far north (~10 g/kg @ H85).

With each model run I continue to compare forecast sounding indicies with Jon Davies low-CAPE tornadic supercell numbers, and many are eerily similar. Given the strong deep layer shear, I'll take my chances that something surface based can develop in the warm sector. Given the chase area is 4 hours or less from home, I can't sit this one out.

 

[Jesse Risley]

I just hope the low CAPE environment doesn't bust us on this one, but helicity values are respectable. I'm liking the WRF better than the GFS at this point. The warm front should be able to reach the I-74 corridor before mid-afternoon tomorrow, but I could see it being held closer to the I-72 corridor as well. The ultimately track of the low pressure system will be crucial to how far NW the risk extends.

Depending on where the best CAPE ends up and how far north the warm front advances, I plan to target an area SE of a Macomb-Galesburg line, possible even east of the Illinois River if time permits.

 

[Andrew Pritchard]

Well it's never fun to wake up to a blanket of clouds, but the models continue to insist that the system will wrap up and that warm front will really surge north here after about 9 am. I still don't think that it will take a ton of instability to set off a low topped supercell or two and the RUC is lifting an area of nearly 1000 j/kg up to Interstate 72 by 21z. Low level shear is still bonkers in that area along the warm front so I can't pass up the chance that something does develop in that area beings how it would be about an hours drive for me. I'm not sacrificing much at all today so it's a no brainer to at least give it a shot.

I'll probably hang here in Champaign a little longer and let things get their act together, but plan to hit up a Springfield to Litchfield line on Interstate 55 by around the lunch hour, possibly a little further west towards Jacksonville depending on where initiation looks to occur. Interstate 55 will give a nice north and south option to adjust to the low track and warm front position. It's hard to believe how fast the models want to lift us into the warm sector, but they've been consistent so I'll give them the benefit of the doubt at this point. I guess I'd rather they be consistently wrong, rather than all over the place and making me throw a dart at the ole map.

I am still keeping an eye on south central Illinois however, along Interstate 70 and may adjust down there if I get the sudden urge.

 

[John Farley]

Well, I am in an "I'll believe it when I see it" mode. Although the RUC still projects the warm front and track of the low pretty close to STL, I have my doubts about enough heating and instability making it north to get much severe in MO or IL, except maybe in the far southern hills and trees. The widespread rain across MO and the low temperature and dewpoints across both MO and IL are discouraging, to say the least. On the upside, if enough warm moist air advects northward to get storms going, it still looks like plenty of shear. Hope something does happen, because if it does, it would be a nice local chase for me, and this is one of the relatively few days before late May that I am able to chase.

 

[Scott Weberpal]

The moisture is well on it's way (~60F dewpoints in NE AR), advection and mixing in the next few hours shouldn't be a problem at all...may have 60F dewpoints to BMI by 00z. Cirrius shield is another issue. Looks like E. IL has maintained at least partial clearing, and if that clearing remains may set up a thermal boundary across C. IL which could be another focus for storm development. I may head out around noon to arrive in the Decatur area by 4 PM.