2014-07-11 FCST: NE/IA

[Royce Sheibal]

SPC hasn't jumped on Friday yet, but I think this will be a sneaker. GFS and NAM agree on leftover convection hanging around from another overnight MCS friday morning. NAM pulls near 100 degree temps up to SE NEB but GFS keeps things at 90. NAM shows strong cape and helicity on the Iowa side with caps breaking between 4 and 7pm. GFS is more bullish toward nebraska with cap breaking in the same timeframe.
If NAM hold true 850 winds are pathetic and expect any storms to be trainers with hail, but if they align themselves along the warm from (as they tend to do) we may get a spin-up or two on any storms that grab the local vorcitity. There was a tornado in Arlington, NE back in 96 with a vary similar setup, but other than central IA i think LCL's will be too high.
If GFS holds true 850 winds will be in the 30-40kt range and SRH goes up, surface temps go down, and LCL's get down to a better level for tors.
I have friday off, but unless I finish this emergency management final tonight, I won't be able to go out. What do you guys think, good day to chase a summer storm? Or will the cap hold and make it a bust?

 

[Skip Talbot]

Looks like a cap bust for surface based supercells in Iowa to me. CINH and LSI values are showing a really stout cap in the Iowa warm sector. Then there's issues with lift with only 20 knots at 500 mb hitting that elongated surface low, and just a little puff of northwest flow well north of the warm front. Slight height rises are also no good. It's July though. 12z NAM actually showed the warm sector opening a crack in the cap there, but it looks pretty solidly shut on the 0z. Worth watching, but definitely looks like a very isolated, conditional chance for now. If that cap is open though, there's great veering wind profiles. Hodos are small but have nice little loops, strong to extreme instability, thanks to those mid 70's dews. Looks good other than than those capping and lift issues.

Behind the low in Nebraska where we've got northeast surface winds, the models are blowing up convection. That's probably going to be your hail show with at least partially elevated storms? Looks like a summer setup to me, where storms are firing around the rim of that dome of hot air, and nothing can quite root to the boundary or become surface based, and only turkey towers and orphan anvils go up in the warm sector if anything.

 

[Royce Sheibal]

Latest model runs from NAM and GFS both slow the low down to a halt. What was looking pretty good on the Iowa side, but now it looks like the cap won't break, or it may get ruined by the leftover MCS. GFS still wants to blow up convection on a narrow band along the warm front around 7pm, where helicity will be locally increased, but NAM calls BS on the eastern convection, instead putting it closer to the low out in West Neb. This is gonna be one of those days where we won't have a clue till tomorrow morning or even mid-day. ML LCL's look good for surface based to the east if anything does go, but that chance is lowering by the minute.

 

[Skip Talbot]

Still watching this one fairly closely. The LSI plots have actually been trending favorably, with the 18z NAM showing a big fat hole in the cap over central Iowa by 0z. I don't put much stock in that run, but it's nice to see the positive trend. The low level jet really kicks in after 0z, causing the effective SRH and tornado parameters to spike. If we can get a sustained updraft off the nose of that low, it's going to be tracking into an environment becoming more and more favorable toward sunset:

 

[Skip Talbot]

This morning's RAP and HRRR are significantly less optimistic about chances for storms across Iowa. Both models are showing significantly less instability and moisture. It looks like the lapse rates are taking quite a hit from some warm air aloft too. The cap is also thermonuclear with < -200 CINH over sw IA by 0z. Yikes. Iowa was probably a wishcast from the start though with that upper level high sitting over the central plains and its ridging and height rises.