9/17/10 FCST: KS/NE/IA

[George Limpert]

I haven't looked too closely at the setup for 9/17, and intend to do so this evening. Upon initial inspection, it seems worthy of a thread.

Severe weather appears possible over a small region of northeast KS, southeast NE, and southwest IA. Convective inhibition should prevent thunderstorms from developing until late afternoon, but storms should develop near the cold front. Moderate instability can be expected ahead of the front. Bulk shear should be sufficient for a few supercells in the late afternoon/early evening. Tornado potential appears to be marginal, but not zero. I agree with SPC's day 2 AC that the best tornado potential appears to be along or just behind the cold front where there should be better shear.

Certainly it's not that impressive... but it's September.

 

[Royce Sheibal]

The latest RUC models have some serious 500+ 0-3KM helicity all afternoon and evening in central / western NE. Cumulus field is popping to the N right now. SPC still has NE in 5% for tornado, but all the cape is down in KS. Tough call today, maybe we'll go out.

http://weather.cod.edu/forecast/RUC/SP/rucSP_3km_hel_9.gif
Target: Grand Island, NE.

 

[Greg Blumberg]

The special 19z sounding verifies what I was thinking earlier about the 12z sounding. The lower levels have been warmed via warm air advection and CAPE has significantly increased. This is a really iffy scenario.

Over the past few hours, the temperature gradient of the boundary that lies W-E on the north side of the Iowa-Nebraska border has strengthened. I can definitely see the boundary being an additional source of forcing for this event but I have my doubts on how much it will contribute, especially since there isn't really any upper level support. That is one heck of an inversion on the 19z sounding though.

I would suggest the target be refined to an area further west along the boundary, preferably closer to the surface low.