4/30/10 FCST: TX, OK, AR, LA, MO, IA, MN, WI, IL

[E Hale]

OK, so i'll start this thread since no one else has.

Friday is interesting in that the Highest probabilities per SPC are in AR and N. LA, but i'm seeing a greater TOR probability for due to discrete nature of supercells in initial firing in Eastern OK and TX. I definitely like the much deeper moisture on Friday, when compared to quality of moisture return on Thursday.

 

[Eric Bucsela]

E Hale- Thanks, you just beat me to this! In E TX, dews and CAPEs will be much better Friday (> 2500 J/kg in TX according to GFS) than they will be further north on either Thu or Fri - and there's less risk of a cap bust. NAM is also progging 10kt SSE surface winds under a 20-30 kt SSW low-lvl jet and ~50 kts SW at mid-lvls. So shear won't be quite as good, but looks ok to me for rotating storms. I'd planned to be in Houston for a wedding this weekend and wondered what chasing is like, say in the Dallas/Waco/Lufkin area (?)

 

[John Farley]

I think IA, WI, and IL should be added to the mix for Friday, as there looks to be decent potential up closer to the surface low. Not great instability, but probably enough, and excellent shear. NAM suggests explosive storm development in northern MO and eastern IA after 21Z. Now with the amount of model disagreement there has been with this system, that might turn out to be off in location, but there would appear to be decent potential, especially in the first hour or two after initiation before the storms get more lined out, somewhere in MO, IA, and possibly IL or WI. I certainly have my eye on both this day and the next one as potential chase days.

 

[Jeff Duda]

I think IA, WI, and IL should be added to the mix for Friday, as there looks to be decent potential up closer to the surface low. Not great instability, but probably enough, and excellent shear. NAM suggests explosive storm development in northern MO and eastern IA after 21Z. Now with the amount of model disagreement there has been with this system, that might turn out to be off in location, but there would appear to be decent potential, especially in the first hour or two after initiation before the storms get more lined out, somewhere in MO, IA, and possibly IL or WI. I certainly have my eye on both this day and the next one as potential chase days.

I think severe weather is much more likely in MO, IA, IL, WI on Friday, but I think it's going to end up being a big honking squall line due to the forcing.

 

[Erik Burns]

I really think Friday has the greatest potential. Although currently looking like a set up in the trees. The NAM has been slowing it down the last couple of runs bringing the Pacific front/dryline east of I35 by 18z in Texas than retreating it back to I35 by 0z. If this sytem slows down we could have chaseable storms in the Central Texas/ North Texas area Friday. NAM brining in 70Tdps, 3,000 J/kg of CAPE, Very little capping. Bulk shear is supportive of supercells but the best LL shear and helicity tends to be displaced further east into the warm sector. Hoping this gets worked out. For sure keeping an eye on it.

 

[Kevin Askew]

Friday and sat. both have potential, Local AFD's mention this as well BUT Sat for our area seems a timing issue. This will likely change but SREF is showing potential as severe ingredients inclunding tornadoes appear likely. Currently targeting SEMO or my area fri for pop up storms. Eve/night in SEMO. Sat Looks like NE AR ATM. Staying in our region for this 2 day setup and play what we comes our way here.

 

[Trey Thee]

I definately feel we have more potential for tornadic supercells on Friday versus tomorrow (in Tulsa at least). If the dryline doesn't move through Tulsa early in the day, there could be chasable storms go up just to the east of I35.

 

[DWest]

I think severe weather is much more likely in MO, IA, IL, WI on Friday, but I think it's going to end up being a big honking squall line due to the forcing.

Even with my limited forecasting knowledge, I tend to agree with you; although for this area (south central MO), that kind of setup is hardly atypical. Still a couple days out though, and as often as the models change who knows what could eventually end up happening.

 

[Stephen Jones]

I think friday will be a very interesting setup. 00Z NAM and 00Z GFS has some differences though. I like the NAM because it is showing more directional shear than the GFS over NE TX. While I'm not wish-casting but NAM has been a really good model so far compared to the GFS in my opinion.

With both models showing CAPE above 2500JKG. Anything can happen. Hopefully the LLJ gets placed farther west closer to the dry-line into E TX by 0z Saturday. Still alot to be determined with this system but I think we can see some nice Supercells and a Tornado Potential going up in E TX and into Shreveport, LA up in AR! Dewpoints and moisture return should be fairly decent (Into the Upper 60's and lower 70's). Further north i believe will be more of linear nature as the sunsets... Maybe a small window for tornadogensis... We shall see.

 

[Chad Cowan]

Feel free to call it a geographic bias and stay away, but I'm really liking the ern KS target for Friday. Some precip forecasts (including the 0z NAM) have been clearing the squall line out of this area by late morning, which combined with strong moisture advection will allow for rapid destabilization. Storms would fire first along the surface front in northeast KS into southern IA in late afternoon and then possibly southward, along the dryline as the cap erodes. +80 kts (!) of effective shear along with moderate instability will promote the rapid development of rapidly moving supercells. We've got climatology and synoptics pointing to a big tornado threat over a big area, we'll just have to wait and see how the mesoscale plays out.

Again, the placement of the secondary surface low along the front will dictate the amount of low-level turning and the overall tornado threat. If the track is similar to what the NAM is thinking, it could be a big tornado day in the KC area.

 

[Brett Adair]

The coupled jet structure entering Arkansas should prove interesting by afternoon and early evening. The left exit region of the STJ is going to punch into the Ozarks/Mid-South and promote the rapid formation of supercells along the low level jet axis by Friday afternoon. Central/East Arkansas could get hammered if instability fields verify given the kinematic environment progged.

Plenty of potential back into OK/N TX where the frontal forcing may play more of a key role in developing convection in the afternoon as the pre-frontal airmass becomes unstable. Further east....the divergence over-top should aid in eroding the EML cap and yield more discrete convection given the weak forcing over this area. Storms should also be very chase-able with motions of 25-35kts.

I will be targeting somewhere around LIT on the I-40 corridor.

 

[Dave Marshall]

It looks as if MS could be added to the topic. The area from I-55 west to the river (unfortunately *very* tough chase country) looks primed over the last couple model runs. Soundings in the morning across most of LA, southern AR, and western MS approach a 'loaded gun' appearance and instability seems to be quite high. As the day goes on, hodographs also seem to perk up with modest low-level curves and some nice speed shear.

The 12z NAM is making Iowa look interesting also. Awesome kinematics. Instability could be a real problem though.

 

[Andrew Pritchard]

Definite improvement on this mornings runs. My biggest concern is actually storm motion. These cells could be moving upwards of 50 mph, so if the storm of the day ends up over an area of rugged terrain in northern MO or SE Iowa you're hosed. Pretty broad target right now, as anywhere along I-35 from Des Moines to northern Missouri stands a chance at seeing a line of supercells develop. Right now, my slightly less broad target region is right around Ottumwa still, Ottumwa to Iowa City to Waterloo maybe. It's hard to nail down a more specific region with such fast storm motions as the storms may enter and leave my triangle within an hour. I'll probably start the day around Iowa City, simply to be far enough ahead of the boundary that initiating storm do not quickly pass me up before they organize. There should be a few tornado reports between highway 34 and highway 20 in eastern Iowa. There could be isolated supercells down into Missouri, but right now I think the highest concentration is going to be in eastern Iowa.

Morning debris should erode by late morning, allowing for sufficient destabilization by mid-afternoon for explosive development along the front right along Interstate 35 from around Des Moines south into far northern Missouri. These storms should then race NE into my target triangle by early evening, likely producing a couple tornadoes along the way. 0-1 km helicity values could exceed 350-400 m2/s2 as the low level jet absolutely screams into eastern Iowa, so given sufficient destabilization I wouldn't be shocked to see a more significant tornado in SE Iowa right around Ottumwa, and simply owing to the fast motions, potentially a couple decent tornado tracks.

So anyway, fairly broad potential area for svr and tornadoes across all of eastern Iowa and northern Missouri, but I'll favor SE Iowa right now for a couple good tornadoes. Storm motions are going to be the big kicker on what could otherwise be a pretty fun chase. Speckled tornado reports are a pretty good bet in my opinion, but my bet is a lot of chasers come out of this one pissed off and bummed out.

 

[Derek Weston]

Have my eye on the mid/upper mississippi river valley for tomorrow.

Two big questions are. . . . destabilization, and turning with height. (where tornadoes are concerned)

Looks as though moisture return ought not to be a problem. Worry will be ongoing precip and whether or not we get a big enough window to heat up.

Not sure we have the sort of shear needed to support discrete cells too long... if I had to guess, quick upgrowth into a QLCS.

It's borderline. That said... should we have "enough" turning with height for tornadoes, and with enough instability. . . we could have some rather dangerous storms. By 0z the low level jet is roaring at 50kts + the eastern half of IA/Missouri... coupled with a mid level streak at near 100kts, and you're going to have some very severe weather should instability allow.

 

[Jason Berner]

I also am eyeing Iowa and Missouri. Instability does seem to be a problem but the models have trended way back over the last few days on the amount of junk convection that is left over from Thursday nice but that has still only had a minimal effect on the amount of instability present. Still looks like we could see up to 1000 J/kg of CAPE across N. Missou and S. Iowa. Areas of 60 kt shear make me think that some isolate supercells will go up but the overall storm motion and shear pattern looks a lot like a big squall line not long after initiation.

I think I am targeting N. Missouri (Kirksville or 20 miles or so North). It isn't the greatest country to chase in but, in my opinion, is the most likely place to see more isolated supercells capable of some brief tornados before the whole system lines up later into Fri. night.

P.S. I am pretty new to actually trying to forecast severe weather so if there is anything that seems off with what I have to say, let me know so I can check it out and try to learn.