2014-09-09 FCST: NE/IA/KS

[Royce Sheibal]

Tuesday is looking very exciting, but at the same time it has the feeling of a total letdown just like the 9/1/14. The models in the last month to be over prediciting cape and helicity in the wake of morning/existing convection and things just couldn't get going on previous days.

That being said, lets take a look at the models. The 06Z NAM has morning / existing convection hanging around E ENB and all of IA throughout the day tuesday. Despite this, ML cape is still 2500+ and surface cape (if we can get surface based) is even better, but the surface may be capped. 0-3 SRH of 715 at 0z just SW of OMA? Yes please. Big scary looped hodographs with storm motions almost due east. I can't wait to see what the 12Z Nam thinks.

The GFS doesn't totally agree. It would seem the GFS thinks existing convection will ruin the environment in E NEB, and that NE KS/ W IA will have better cape, with NE KS having the best SRH. On both models ML LCLs will be low, and the existing stratus deck from prior storms can be encouraging for tors, but only if we get destabilization on the south side. Storms will likely cross into IA and at some point go MCS.

I have class tuesday, so no chasing for me, but IF I were to go, I'd be around Eagle, NE. If morning convection is too heavy, I might consider re-targeting further south near the KS/NE border. I'm not sold on IA being chasable tuesday, as much of the risk will be near dark and or ruined by the MCS.

 

[Todd Rector]

I *might* head out tomorrow afternoon, depending on how things look in the morning. I am getting really tired of the MCS lines and HP shows in Nebraska this year. Luckily it's a relatively short drive for me.

 

[Skip Talbot]

Surface pattern and placement of features looks similar to 9/1 and I'm looking at targeting the same areas on this chase: initiation in south central NE, southeast NE supercells, and maybe a tornado play as storms approach Iowa by dusk. The NAM was showing huge looping hodographs last night, and still is just after dark over Iowa, but the 12z NAM took things down a peg, slacking off the midlevel winds and even the low level jet a bit.

Here's what I don't like about this setup:
The timing appears to be slowing down or the strength of the system weakening with each run. It's a bad trend, and the NAM is backing off the winds. We've got 30-40 knots at 500 mb at 21z over NE when and where I'd expect storms to pop. We really need some strong flow to vent storms, and promote supercells rather than a quick transition linear modes.

Storm mode again looks to be an issue. Very high precipitable water, slow moving storms, low LCLs, and weak jetstream winds favor an HP storm mode.

Storm coverage and ongoing precip. NAM is showing some ridging and a strong cap in place on Tuesday morning, but it's also got much of NE and IA completely socked in with rain and clouds during the day. The cap is wide open at 21z, and this should be good timing, but I'm worried about the whole warm sector going up in a big MCS again. The NAM has a shortwave moving through eastern NE into Iowa by evening and overnight, this might further promote this evolution after storms have congealed.

Like 9/1 I'd expect storms to fire off the nose of the elongated surface in north central KS into south central KS. Storms that can remain discrete have a shot at producing as they approach very favorable low level speed and directional in east central NE into Iowa. That's ultimately what doomed 9/1 though. Storms fired well west of the favorable shear over Iowa, and we had a congealed mess by the time the line made it there.

Preliminary target is Hastings, NE due to the westward trend of each run, and where there may be a more favorable mix of stronger capping/higher LCLs to promote a more discrete and classic storm mode before storms tap the favorable shear along the warm front currently plotted near I-80.

A cherry picked hodo from last night showing 1400 3km SRH and 40 knots of 1km speed shear:

Even if we do have a solid line hitting Iowa by later in the evening, the excessive shear may still allow for some embedded supercells with a tornado potential. I wouldn't consider these storms chaseable at all though since it will be after dark and circulations will be completely rain wrapped.

 

[Royce Sheibal]

Things are starting to get interesting. MCS is moving over NEB as expected...but little micro-cell storms are forming in lines across E NEB right now long the warm front. This entire area is getting incredibly unstable, just gotta hope the southern flank doesn't fill in before prime heating. The structure of these little cells indicates medium quality shear environment locally, those that favorite multi-cell development, however its still very early and shear should push more toward discrete supercells the further south we go. SPC's SREF has 70% SIG tor ingredients at 7pm, which is nuts, and a 70% chance of 2k cape/40kt shear+precip at the same time in the same area around SE NEB. 2k/40/precip is probably my favorite SREF they publish and is usually what I use for targeting (because its the median for sig tors in Nebraska). Those of you who are out there, good luck, precip waters of 2.5 means HP monsters, and a strong chance of after-dark tors if they can remain discrete. I'm still sticking with Eagle, NE as my target for now, as I think that cells forming in N KS will push into the mega-shear zone located in this area around 7pm. Similar setup to the Hallum, NE setup a few years back, same locations too.