6/1/10 FCST: NE/IA/MO/IL/WI

[John Peters]

6/1/10 FCST: KS/NE/IA/MO/IL/WI

setup for the MO/NE/IA junction looks eerily similar to Hallem NE tornado from May 22, 2004.

0Z nam is fairly consistent with previous 18Z, aside from details related to the shape of precip.

Impulse within the quasi-zonal UL flow regime and associated LL jet nosing into N MO will initiate widespread convection along the warm front - as LLJ ramps up during the late afternoon/evening, enhanced 0-1km SRH will contribute to 0-1km EHI of 6-7 right near this junction.

Looks like a progressive derecho type event, but given the favorable LL sheer profiles along the southern end of strengthening MCS, I wouldn't be surprised if we see embedded supercell structures and perhaps a few more intense supercells just SE and ahead of the main line - similar to what we saw back on May 22, 2004.

Edit: compare also to May 8, 2009

 

[Stan Rose]

I agree about the shear and LLJ, John. I chased Hallam (caught up at dark) and there was quite a bit of discrete cell development in the warm sector (front was a bit farther north/west) but there are some similarities here. I wont be able to get that far east so im hoping for early action north and east of the surface low, hopefully as far west as ITR or GLD. If the moisture can hang on there and storms can stay rooted in the BL (unlike yesterday's NE deal) there should be some localized helicity there to get a good storm or two going.

 

[jshields]

i've been watching this for days now too, and to me the models have some differences that are fairly substantial on the 0Z run and the last several runs. first off the nam is much warmer w 90+ degree temperatures all the way up into eastern nebraska and the 70+ dewpoints are actually east of this heat axis in iowa, so in nebraska i'd be worried about temp/dewpt spreads. in fact the lcl heights on the nam are over 1500m at 0Z wednesday. the nam has been showing the higher temps for the last several runs when compared with the gfs as well. the main reason the nam is so warmer it looks like is bc it doesn't really break out any precip til sometime after 0Z bc by 06Z there is heavy qpf in western iowa. bulk shear with the nam is also much lower over central/eastern nebraska into northern kansas with nothing greater than 30 kts showing up until you are into iowa. the nam has the surface winds veered over much of nebraska and northern kansas, and not really backed at all until southern iowa. by 03Z on the nam everything gets a lot better with the llj, but by then cinh has increased like crazy so you'd have to be worried about elevated storms only. the gfs keeps the 90s in western kansas, and in fact keeps the 80 degree line in southern nebraska, where the 70+ dewpoints are also in eastern/southeastern nebraska, so the lcl's are way lower(500-750m). the gfs is showing tstorms early in the afternoon over southeast nebraska at 18Z on tuesday and lifting north pretty rapidly. also the bulk shear is nearing 45kts over most of eastern nebraska with looping hodographs. wxcaster forecast skew-t's are showing srh(0-1km)> 200 over most of southeast nebraska as well at 0Z wednesday. so at this point i'd love to keep the temp/dewpt profile of the gfs and the forecast precip of the nam model. either way i will be out chasing in southeast neb/southwest iowa.

 

[Mikey Gribble]

The NAM and GFS paint very different pictures on the setup and extent of any tornado threat tomorrow. I haven't been watching this closely, but I have glanced things over with each model run for several days now and the GFS has been fairly consistent in showing a decent setup for tornadoes over southeast Nebraska. The NAM hasn't been as consistent and hasn't looked quite as good for tornadoes. I was really surprised to see that SPC made no mention of tornadoes in their latest outlook. Based on their wording and placement of the risk areas over the last couple days it seems like they might be leaning towards the NAM with this one. I'll go with the GFS because I like it more lol. No, I have done only minimal forecasting over the last couple days so I really have no business making a post on this. I plan on doing that now since its decision time for chasing tomorrow, but I will likely be heading out. The GFS shows an outflow reinforced frontal boundary near the KS/NE border which looks pretty good for tornadic storms. Some of the composite indices are hitting up there pretty high with the GFS. Sig tornado is around 10 now.

 

[Mikey Gribble]

I am totally baffled on tomorrows forecast. I haven't really be watching this closely with the models and I've only spent a couple hours working on it today, but man this is a tough one. I'd hate to be putting out a forecast for the general public because unless the GFS is totally out to lunch, this one has flop potential written all over it. I did attempt to do some forecasting, but I've pretty much given up on it now. I'll let the guys that are smarter than I am figure this one out and I'll just follow what they say.
I'm just going to copy and paste the post from my blog. I put a map up there too if you're interested in seeing it here is the link http://loadedgunchasing.com/blog1/

Above is a map of the GFS solution for tomorow, which is very different from what the NAM is showing.
There is major disagreement regarding critical details with tomorrows setup between the NAM and GFS. I have no idea which one to believe. I hope the GFS verifies because it looks pretty good. The NAM isn’t so good. I haven’t been paying close attention to this setup so I’m in the dark on model performance over the last several days. SPC seems to be going with the NAM, but that is just a guess. If they were taking the GFS seriously I think they would be mentioning some tornado potential.
This is a very complicated forecast and I haven’t been spending as much time working on this as I usually do, so take it with a huge grain of salt. I focused primarily on the GFS and made my map based on that. I also tried to figure out the root cause of some of the differences between the GFS and NAM. I’ve only been working on this for an hour or two and solving the discrepencies between the two models is way over my head, but the primary difference effecting the tornado potential tomorrow seems to have a lot to do with overnight convection. The GFS breaks out a cluster of thunderstorms tonight over west central kansas, that tracks off to the northeast and along the KS/NE border through the day tomorrow. The NAM does not show this convection.
With the GFS the overnight convection along the border reinforces the frontal boundary and strongly backs surface winds over the southeastern portion of Nebraska. It also serves to keep surface temperatures down so that the temperature dewpoint spreads are low enough for a good tornado threat. The NAM doesn’t have this outflow reinforcement and doesn’t back surface winds and has much higher temperature/dewpoint spreads as a result, killing the tornado potential.
Further complicating the forecast is the fact that there is no real upper level support. There are only minor disturbacnes moving through largely zonal flow. There are differenes between the two models regarding the finer details of the mid level flow/disturbances as well. Both models do show around 40kts at 500mb over the target area tomorrow afternoon though and when combined with strong to extreme instability that should be adequate for supercells.
I have absolutely no idea what to expect tomorrow. With one model you have >300 0-1km SRH along the boundary in SE Nebraska and with the other one you have about 100m2s2. There is just way too big of a spread with these sorts of details and the surface pattern to know what is going to happen. The picture may become a little more clear later tonight when we see what overnight convection is doing. The latest run of the RUC does not show convection developing over west central Kansas like the GFS does, but the latest run of the RUC only goes out to the forecast hour before the GFS develops convection (the RUC also sucks something fierce at predicting convection).
Due to all the uncertainty and the minimal time I’ve spent working on this I’m going to have to lean on SPC a lot more than I usually would. Whether or not I chase tomorrow will totally depend on what they are saying and on whether or not the GFS looks like it is verifying. If the GFS looks like its verifying I will be on that like a duck on a june bug, but if the NAM looks like its verifying I will sit this one out.
I will update routinely between now and tomorrow afternoon as I get a better handle on the forecast.

 

[jshields]

yeah its pretty scary how different the nam and gfs are still. the gfs is showing 0-1 srh values over 300 in extreme southeast and southwest iowa at 0Z tomorrow night while the nam keeps the values down around 150 or lower and the max is down in northwest missouri. the wrf actually doesn't even break out any storms, until a line of storms moves through eastern neb and western iowa after midnight. i don't think that it is correct though! the nam and gfs are showing cape values over 6000 along the kansas/nebraska border too hopefully, the gfs wins out and is correct with the srh values bc we could definitely see something big in southeast neb/southwest iowa

 

[Skip Talbot]

Definitely a tricky forecast with large model differences as Mikey has pointed out. At this point I'd be willing to chase the GFS's solution, but not the NAM's.

The GFS has a nice veering wind profile with backed surface winds, and a rich moisture tongue extending up the MO river into SE NE with strong surface heating that will result in extreme instability. There looks like a weakly defined warm front setting up just north of there through central NE and IA that will increase the low level directional shear. The combination is causing the severe parameters to spike pretty hard with sig tor values over 7 at 0z. If surface based storms fire in this environment, the parameters strongly favor supercells and tornadoes.

The NAM, on the other hand, has a very mediocre surface setup. The winds are less backed being almost southerly, and the warm front sets up well north of where the GFS has it, putting it along southern SD and MN. Instability although still strong is lower as the moisture plume does not look as nice. Shear profiles are far less favorable. Sig tor values are an unimpressive 1-2 at 0z across SW IA/NW MO due to an absence of any significant helicity. The marginal shear and mediocre winds make me think that some short lived supercells are possible, but clusters and segments may be more likely, if storms manage to fire in SW IA.

Both models do share a similar set of problems that might preclude a chase altogether. First, what is our lifting mechanism and where are our upper level dynamics? The NAM is not showing much in the way of boundaries. A focus point for initiation is not readily apparent, except way up in MN/SD where I'd be expecting more of a early/linear show as ongoing storms build down to the south. The GFS hints at the warm front being further south, but its not a very tight boundary, and with only 30-40 knots of midlevel flow that's zonal and diffuse, we might not have the upper level support for initiation, or even enough to maintain supercells. The further west you head into SE NE the stronger the cap looks like its going to be and the higher the LCL's. The NAM was showing a stout cap over SE NE and LCL's approaching 2000. If any storms fire here, they'll probably be elevated hailers. SW IA looks a little better in this regard, but again, speed shear is going to be light and I don't see much of a focus for initiation. The GFS is sporting similarly high LCL's but is not as not as harsh with the cap in SE NE as the cap index goes to 0 at 0z. However, this won't be realized if we don't see the 70+ dewpoints and temps approaching 90 that the GFS is showing. The 4km WRF does not break out any storms over the SE NE/SW IA target, nor does the NAM or GFS, only indicating ongoing convection further north where more of an elevated/linear mode is expected.

A glimmer of hope on the 4km WRF is that there is a cluster of storms forecasted to be ongoing across NW MO at the start of the period. This may lay down the outflow boundaries necessary to aid initiation and enhance the low level shear for later supercells. We'll have to watch tonight and tomorrow morning to see how this evolves, however.

At this point the setup looks undersheared, with little focus for a questionable initiation. I'd keep an eye on the GFS's solution though as its far more favorable, as well as how tonight's storms influence the environment in terms of laying down boundaries.

 

[Chris Campbell]

I'm far from an expert, but so far, it looks like the NAM/ETA is correct. It showed heavy precip in SE CO and SW KS between 0z and 6z. Right now there is a tornado warning on a cell in SE CO. The GFS didn't predict any precip occurring in that region at all.

 

[Mikey Gribble]

That definitely lends more credibility to the NAM on precip, but you have to be really careful doing that Chris. When you are dealing with models its not an all right or all wrong kind of deal. One model may be right with that convection with upslope flow or whatever caused it and then be wrong with some convection over Missouri with some WAA precip (just an example). One model may have the surface pattern nailed while its out to lunch on the upper level wind fields. When a model gets one thing right it by no means is proof of it being right in its entirety. Its a little more complicated than that.
I'm not saying the NAM doesn't have this setup right. All I'm saying is the NAM having convection over southeast Colorado while the GFS doesn't implies little more than the fact that the NAM got the convection over Colorado right. And you certainly can't extrapolate that fact and say it will have convection or boundary placement right tomorrow because it was right today over southeast Colorado. Hope that makes sense.

I don't want to ramble, but there are exceptions to the rule I just listed above. I'm walking out the door to go fishing right now though and this is a forecast thread.

 

[Jeff Duda]

The more I look at this setup, the more it begins to resemble that of April 5th this year in almost the exact same location: great thermodynamics and low level shear, but minimal, if any, upper level support and potential cap. WRF ensemble BUFKIT soundings from the quad-state area (SW IA, SE NE, NE KS, NW MO) certainly didn't give much consideration to generating convection in a decently sheared environment. Ugh...

 

[Chris Campbell]

That definitely lends more credibility to the NAM on precip, but you have to be really careful doing that Chris. When you are dealing with models its not an all right or all wrong kind of deal. One model may

This is still probably oversimplifying it, but mainly I was looking at where precip was going to break out, because the talk was that outflow boundaries from morning thunderstorms could be focal point for new storms later in the afternoon, as is, in my understanding, fairly common. GFS appeared to shift the precipitation farther northeast, into north central kansas and southeast nebraska. My thinking was that maybe this precip would materialize farther southwest, more as NAM was predicting, meaning there would be no outflow boundaries in southeast nebraska.

Interestingly, NAM now seems to be putting storms in south central into southeast Nebraska in the morning, unlike before.

 

[Skip Talbot]

It would have taken a lot to change my mind after seeing this morning's run, and the 0z run of the NAM is doing just that. Its substantially improved and much more in line with the GFS. Both speed and directional shear are up as a small impulse is forecast to move in with backing surface winds over SE NE/NE KS/SW IA/NW MO. 6km bulk shear of 40-50 knots and 1km SRH of 150+ could support a few tornadic supercells. The cap looks manageable with large areas of erosion by early evening and the NAM even breaks out storms on the NE/KS border at 0z. If this run is accurate, than there could be quite the show on the NE/KS/MO/IA corner tomorrow. Prelminary target is Seneca, KS for 0z initiation of tornadic supercells.

 

[Chris Hayes]

This is still probably oversimplifying it, but mainly I was looking at where precip was going to break out, because the talk was that outflow boundaries from morning thunderstorms could be focal point for new storms later in the afternoon, as is, in my understanding, fairly common. GFS appeared to shift the precipitation farther northeast, into north central kansas and southeast nebraska. My thinking was that maybe this precip would materialize farther southwest, more as NAM was predicting, meaning there would be no outflow boundaries in southeast nebraska.

Interestingly, NAM now seems to be putting storms in south central into southeast Nebraska in the morning, unlike before.

Chris, I saw that on the 18z NAM earlier but was hesitant to post it. Yes, prior convection during the night before a chase day can be helpful during said day. There are good and bad things about night convection. Good thing is it can throw down some outflow boundaries to fire new storms or really crank up existing storms. However it can also leave a cloud shield around that can prevent adequate destabilization. May 9th of this year there was worry that MCS development might hinder destabilization for the expected outbreak in Oklahoma on the 10th. However, MCS development occured over eastern, OK and cloud shield was able to clear in time. No good boundaries were left over but it didnt leave a stabilizing cloud shield either. Back to tomorrow. SPC's 01z outlook issued a couple hours ago makes mention of some storms firing later tonight over central Kansas. IF those storms can fire, they might throw down sound boundaries for tomorrow. Latest infrared sat image of Nebraska shows what appears to towering CU over NE CO and SW Nebraska. I'm not good at interpreting infrared satelite yet, so someone please correct me if I'm wrong on that. Hopefully those CU will be the start of initiation for some storms tonight to act as a bit of a force to keep the warm front from surging too far north tomorrow.

 

[Mikey Gribble]

I'm on board with you Skip. The 00Z NAM is showing a setup much more similiar to the GFS. It shows the frontal boundary near the KS/NE border. It is breaking out convection along the border like the GFS in the AM, which will help to lay down a boundary and back surface winds. It lowered the temps and keeps the temp-dewpoint spreads down similiar to the GFS. This is a big boost to tomorrows potential.
Slow moving storms, strong instability and good low level shear for this time of year all look like they could come together for a great chase day. This is a pretty solid setup for tornadoes. My only problem is that I don't like how the 850mb winds are sort of sloppy.
When you consider that we have been getting decent tornadic storms regularly over the last several weeks with mediocre setups you would think that a fairly good setup like this would have to produce. There very well could end up being fair number of tornadoes tomorrow from north central Kansas into southeast Nebraska. It definitely looks like game on to me. I would think SPC will ramp it up quite a bit in the next outlook if the GFS stays on track.

 

[Bill Schintler]

Chase Target for Tuesday, June 1

Chase target:
Fairview, KS (extreme northeast corner of KS).

Timing and storm mode:
Storms will develop in the area between 5 and 6 PM CDT. Supercells will be likely early in storm evolution, with a transition to a derecho with an attendant severe wind threat in south-central and later in southeastern Iowa. Looking ahead, the active pattern will continue for the remainder of the week, with periods of storms through Wednesday afternoon, and again Friday night into Saturday.

Discussion:
Low pressure aloft over the Hudson Bay area will shift to the east during the next 12-36 hours. At the surface, a frontal boundary will extend northeast from low pressure over western KS at 00Z, 06/02. This boundary will provide the focus for thunderstorm initiation Tuesday afternoon. Another area of surface-based convection should fire well ahead of the front in Mid-60 s dewpoints will advect northeast into eastern NE and western IA by late afternoon. MLCAPEs will increase to as high as 3500J/kg as steep mid-level lapse rates in excess of 8C/km overspread the area. Two areas of elevated convection will be ongoing early in the period. Storms should be ongoing over southeastern SD, and southeastern NE/northeastern KS, in a zone of isentropic up-glide. The southern MCS should weaken by mid-morning; however, the SD convection will increase in coverage while expanding into MN by late morning. A resulting outflow boundary will push south to southwestern IA by 18Z.

Storms should initiate along an outflow boundary by 19Z at the exit region of a 50kt H5 shortwave. Strong instability coupled with a strengthening mid-level jet will support widespread damaging winds. Overnight, storms will continue to focus at the nose of a 50kt H85 LLJ. This will result in training of convection with very heavy rainfall with precipital waters increasing to 2 inches south of I-80 in IA. Flow aloft parallel to the boundary will support training of storms overnight. Looking at model performance, the ECMWF has had the best run-to-run continuity, and indicates a more northerly frontal position and surface low track then the GFS and NAM.

- Bill Schintler

10:46 PM CDT, 05/31/10