4/03/11 FCST: KS/OK/NE/MO/IA/IL

[Greg McLaughlin]

The RUC is notorious for over-forecasting surface dewpoints and therefore also over-forecasting CAPE values. Because mesoanalysis products are also based off of RUC model output, it is redundant to compare the two. It appears the RUC is thinking widespread 65+Tdps will be common in the warm sector today. I would assume we will see low-level moisture mix out to a degree under strong surface heating. The exception may be along the warm front and near the surface low. 12z soundings across the entire region show a formidable cap in place. I don't see any surface based storms breaking through the cap during the daylight hours, except maybe in Iowa and northern Missouri. The most recent HRRR likewise suggests this.

 

[Brian Mette]

I'm still not 100% sure on where I want to target for today. I don't have time to go all the way up to the eastern KS target area (I have to be up bright and early tomorrow morning.) So right now, I'm debating between southern or southwestern OK, and north-central OK/south-central KS.

I'll admit S-SW OK is definitely a long shot. However, I think if a storm did manage to break through the cap down there, it would go absolutely nuts. Plus, I'm betting a majority of the storm chasers will be up in eastern KS, so there will be less chance of a chaser convergence.

I'm liking north-central OK and south-central KS, though. NAM does show a little bubble of precip forming there at 03z, before it eventually merges with the rest of the line of storms. CAPE is looking pretty good in that area, and CINH does seem to die off by 21z. Dewpoints in the area are already in the lower to mid 60s. I'm personally hoping an isolated supercell or two will develop and have a chance to do something before merging with the rest of the storms.

The big question is still whether or not the storms will fire before dark. But at the moment, I'm thinking of targeting Bramen, OK.

 

[Jeff Duda]

One thing I've noticed about the Northern target is the very high RH values near the warm front with very low LCL heights. It seems that there is a possibility that even if storms do develop, which it appears they likely will, tornadogenisis may be hampered due to excessively cold RFD's due to the high relative humidity and low LCL's. The GFS has also significantly dropped the CAPE values of the Northern target to between 750-1500 j/kg, which is still easily enough, but not as beefy as it was in previous runs. I believe that IF storms are able to develop in E Kansas, they will have a much better chance at producing due to better 0-3 km helicity, much higher 0-1 and 0-3 km EHI, and lower RH values. Both targets seem to be a gamble at this point IMO.

I think you may have the wrong idea regarding RH, LCL heights, and temperatures of RFDs. High RH and low LCL heights would imply there is a lot of moisture in the low levels, thus a downdraft would not be able to evaporate as much moisture and would actually arrive at the surface as a relatively warmer feature. High RH and low LCL heights are thus very favorable for tornadoes from a thermodynamic standpoint.

My comments are pretty in line with that of others. 12Z soundings this morning show quite the cap over the warm sector. The really veered surface winds are rather annoying, although the HRRR is showing them not quite as veered as the NAM was yesterday. The northern target seems to be the only chance of seeing a tornadic supercell today, but storm motions are going to be a little high. Farther southwest, the probability of daytime convection is much less, but if something does fire it will probably be pretty isolated and photogenic.

 

[Michael Riedl]

LCL heights and veering low level winds make a souther target around Wichita a tough tornado play. Even browsing the 12z RUC int he MDT risk area LCL heights are progged to be 2000M, that is really high. Its just gonna have to be a Northern Play where SFC winds and LCL heights are better. I'll be out in KS but not thinking there will be much threat for surface based convection.

 

[Andrew Pritchard]

I think the best chance for any tornadoes today will be on the far north edge of the northern target. The 10% tor prob location actually blows my mind in both it's existence and placement. Deep layer shear vectors are almost completely parallel to the boundary down there which just screams an instant linear outflow dominant cluster.

If there is any chance for long lived discrete tornado producing supercells I can't see it being anywhere but right on the triple point in northeast Iowa, and along the Illinois/Wisconsin border. Unfortunately, this is where quality moisture will arrive last, so we may never see CI occur in this region. However, right in the moisture tongue where it curls nw ahead of the surface low I do think there will be a narrow daylight shot at an isolated supercell or two. I'd put my money somewhere around Dubuque, IA. Unfortunately this is a difficult target as it hugs the Mississippi River valley. If I feel there is a decent chance at quality moisture arriving in time, and seeing the cap erode in this region I will likely set up somewhere on the Illinois side of the river just south of the Wisconsin border. I'm optomistic that moisture will arrive literally just in time, and that forcing ahead of the low will be enough to kick off a storm before sunset. While it's certainly getting ahead of the game, I believe that if we do see a supercell or two in this region they could be quite beautiful. With these 'moisture arriving just in time' events you'll often end up with high visibility for this part of the country and perhaps some beautiful structure at twilight. That is of course, if we get a storm to go.

I feel strongly about anywhere in se Iowa and northern Missouri being nothing more than a sunset view of a ragged shelf cloud. Due to locational bias, I haven't even looked at the Kansas target.

 

[Jeremy.Degenhart]

Have to agree with Pritchard here...I've been sitting in Peoria second-guessing myself, so it's good to see someone thinking the same way... I don't really see that great a chance of a good, visible tornado anywhere south of the warm front/triple point setup - at least, in the IL/IA/MO area. Thinking I'll head north for somewhere between Sterling and Freeport, IL fairly soon here.

 

[Logan Karsten]

I agree with the majority of the posts here.

The southern target seems way too capped for anything to go up before dark, as cooling at 700 mb won't be occurring until after dark. North of there, you don't find good surface backing winds until you reach the triple point near northeast IA and southwest WI, but the good thermodynamics seem to be displaced to the south and southwest where winds are veered. I would it would be a good day if you want to get some shelf cloud pictures or general convection photos. However, the tornado threat doesn't seem all that great to me.

 

[Flo Cornett]

We've been discussing this locally too (Platteville/Madison WI). I'm a bit more biased than usual today for this area (NE IA SW WI), but I did want to add that statistically (historically) the NW IL area is not a good producer. Yet the database clearly favors the west (IA) side of the MS river in this area. I've been chasing around here for a few years and nearly always have better success on the IA side of the MS river...but timing, as mentioned, is a major issue here.

Also, if you've never been on U.S.20 in IL through this region, the chasing is simply dangerous with a capital D. The roads tend not to be as likely situated on a ridge top as NE IA and SW WI. I'm trying to talk myself into positioning down south of Dubuque off of U.S. 61.

 

[RMacDonald]

Highest threat spreading in a line from Kansas City to Quincy, IL to Decatur, IL to just north of St. Louis. Quincy, IL area has the greatest threat of Tornadoes, as of 19Z,seeing 0-3Km Shear around 61kts, 0-1KM EHI are 3.4, and 0-3KM SRH around 353 with overall CAPE's around 2000 (J/kg). I think area from Decatur to Quincy will be the most action. As for further south into E. KS and OK into N. TX, again capping is the main issue, but trying to show hints of possible Isolated convection in that area. 19Z City Specific 19Z Severe analysis is uploaded http://smartwxmodel.net/severe.pdf

 

[Greg Blumberg]

Prichard, you're thinking what I've been thinking since early this morning. Initially, I agreed with the 10%, but now I'm wondering why they are keeping it. You didn't talk about the Kansas target area, so I'll take care of that.

Via the observations earlier and even still now, I'm really, really confused as to why there are so many chasers out in Kansas right now. Winds out of the southwest around 1 km since 12 UTC? I'm sorry, but when you have a cap in place like that, if you see that sort of wind profile, it signals that you are only getting more cap (poor terminology, but it makes sense.) When you include that with the mixing that is going on, you will NOT get anything going up unless you have strong large scale lifting or strong low level convergence. The good forcing is too far west. I do understand that it's a Sunday and it is a high risk, high reward type thing, but still.

As for southwest Oklahoma, the cirrus deck has been there for several hours. That plus the cap increasing = bust.

Also, the vertical wind profile all day has been unidirectional, and has been orienting the dryline in a NE-SW direction along with the surface wind flow. If anything goes up along the dryline, I can see it back building and turning into a linear mess (granted it will be severe.) It may be able to get off of the dryline, but I highly doubt it.

Edit: Nevermind! You win for now atmosphere!