6/20/06 FCST: MN / IA / NE / WI / IL / KS

[Mike Hollingshead]

Starting to look like ne NE might be the starting place with a line of cu forming there now. 700 temps are cooling there and the moisture at the sfc is feeding back that way.

Hmm perhaps 700 are actually slightly warming there, lol. I thought they had been cooling. 500 cooling a smidge.

 

[Jeff Snyder]

The speed max near 750mb is a very interesting and unforecast development... As Kiel noted, the Fairbury NE profiler showed ~75kts at 750mb several hours ago; the Slater IA profiler is now up to 65kts near 750mb. The RUC analyses (both on the SPC Mesoscale and in 1hr forecast soundings) are only indicating ~50kts, so I think the 0-3km shear values/parameters may be stronger than the RUC is indicating. Regardless, with CAPE running >3000 j/kg, and >150 0-1km SRH west of DSM, I think there exists a threat for a strong tornado this afternoon IF a discrete supercell can develop. Surface flow remains relatively backed to the west of Des Moines, along the OFB boundary from earlier convection. CINH is currently proving to be too strong for initiation, but we'll see what happens in the coming 2-3 hours. Temps in extreme sw IA have warmed well into the 90s and strong mixing continues (partially encouraged by southwesterly flow not too far off the surface), resulting in veering sfc winds and dewpoints dropping below 60F. My virtual "want-to-be" location is somewhere along or just north of I80 between Avoca IA and Denison, where temps have been able to warm into the upper-80s and dewoints remain in the 70-73F range. Looking at the latest surface winds, it looks like there is some pretty good convergence occuring along that OFB, with 94/59 with SW winds near Omaha, and 88/70 with SSE winds just a little east of there. Temps are a little cool north of Denison for me to get too excited about intiation there (temps largely in the 79-82F range, versus the upper-80s closer to I80).

The areas farther north, nearer the IA/MN border, is slowly destabilizing, but it may be a too-little too-late deal up there. Lapse rates on the 18z MPX sounding were horrible (nearly moist-adiabatic), though that's largely because that area was worked over earlier. Again, initiation is going to be the concern IMO, but I think the best probs are just north of I80 in western IA.

EDIT: OAX 88D appears to show the western edge of the OFB, with some interesting smaller-scale features / kinks in the boundary near I70. 500mb winds on the Slater profiler leave a lot to be desired (~20kts), but higher midlevel winds are located to the west of DSM. In an unrelated area, it's 105F in Guymon OK and Dodge City KS right now... That's toasty.

EDIT2: The boundary is progressing northward rather quickly, so I'm aiming more towards Denison than I80 now... The OAX 88D shows some nice boundary layer rolls (reflectivity in the -5dbz to 10dbz range -- if you use GRx, make sure to set your colortable such that you can see <10dbz reflectivities) intersecting the OFB very near I80 northeast of Omaha right now.

 

[Darin Brunin]

Doug Mitchell, Jordan Wrecke, and I are currently sitting in Denison, IA with not a cloud in the sky. Probably going to start moving a little NW to around the Sioux City area to see what the developing cu field in that area is going to do. Overall, I wouldn't want to be anywhere else than where we are right now but it's just not happening so I guess we'll go give that a ahot.

 

[Bob Schafer]

Not that anybody gives a hoot about my analysis, but because I'm bored, here goes:

The warm 850 and 700 temps in NW IA, as well as meager sfc winds, are suppressing any cu from developing. There is some convergence there, but the sfc winds turn to the N and NE just N and NE of the convergence zone, as if an "escape valve" for the converging theta-e. Sfc pressure of 1007mb in the area is too high to get some UVV out of the convergence.

What little cloudiness I see anywhere in NW IA looks more like convective debris than cu to me.

I wish I could offer some encouragement, but it looks like a cap bust to me.

Bob

 

[Andrew Khan]

Kurt Hulst and I were sitting in Ankeny, IA for about three hours, looking at models for anything and soundings, and just waiting for anything to show up....so far hardly any convection, and just a little cu field. We just moved north to Ames, IA where I am now sitting typing this at a quality inn....so far, this is very frustrating, having to wait, hour and hour on end....I hope this results in something good. The CINH, does look strong, and I am leery, as to if it is/will break at all....

EDIT: NOw stuff is popping up on the IA/MN border....I wonder if that is the predicted area for tornadoes...what do you guys think? I am considering heading north more, and seeing how those cells do, or just monitoring them here.

 

[nickgrillo]

Well, the obvious problem today is the excessive large-scale CINH across the warm sector (with RUC-derived forecast soundings showing a gradual decrease in CINH for a surface-based parcel through most of the evening, especially across central IA) although if we do get initiation in the next several hours, then we'll likely see supercells (assuming an updraft will ingest boundary layer inflow). Low-level shear is quite strong (with local profilers -- i.e. Slater IA -- showing a pronounced low-level WAA profile) which will increase the probability for tornadoes (and induce stronger vertical PGFs which will augment to updraft intensity and lead to stronger low-level rotation) as updrafts ingest the rich streamwise vorticity. Visible satellite imagery shows a region of deep convective towers in southcentral MN, where current RUC mesoanalysis shows locally weak CINH, with another zone of elevated convection northeast of DMX -- which could become rooted in the boundary layer as effective inflow parcels lower with additional low-level heating (with mesoanalysis showing a substantial decrease in CINH across much of western IA with a local region of low LFCs southwest of DMX). It should also be noted that SPC mesoanalysis could be over-estimating CINH a bit. With the strong instability and deep-layer shear, we'd most certainly see supercells if we do get an updraft to break through the inversion

I'd still stick just north of I80 (pretty much along I35) and adjust from there. Its a pretty complex situation today still.