6/21/07 FCST: NE SD KS IA MN MO

[Michael O'Keeffe]

Thursday is shaping up to be a potentially good chase day across the C Plains. The combonation of extreme instability, good shear, and abundant moisture should lead to the development of significant supercells, some tornadic.

An MCS the night before will lead to a few outflow boundries across the region. Specifically S SD, C & E NE into W IA. Storms should initiate along these boundries in the mid-late afternoon hours and quickly become supercelluar with the potential to have very large hail and tornadoes. These storms should persist through the evening before moving east and becoming a monster derecho that should continue all through the overnight and Friday.

I couldn't find a target yet, because the models have been all screwed up lately so it's becoming even more of a challenge to find targets lately.

 

[Mike Hollingshead]

http://www.wxcaster2.com/central_models.htm

Earl's stuff has been working.

I guess I like the area from Sioux City on down the river. This could be a fun one when it comes to picking a side of the river to be on. Upper level winds are pretty crappy, but at least it is showing 50-55 knots at 500mb. 700mb temps don't look too insane like they could be this time of year. 10-11c would work for me. I hope 3 things don't happen. I hope those don't raise as I think they did between this morning's run and last night's. Just don't raise much further if they do. I hope the 500 winds don't decrease much. And I hope sw flow above the sfc doesn't kill the dews. It's not terribly strong, and it should be plenty juicy, so I wouldn't think that'd be an issue. I could see the first two happening though. It's kind of crazy to see good flow in the mid-levels over high instability, without insane capping or big moisture issues, in these parts, given the lack of it this year. It'll be nice when it actually happens.

 

[Brian Stertz]

Looks to me (after scanning over the 12z ETA) like it's going to be a good outflow boundary supercell event in the Carroll-Ft. Dodge IA area in the afternoon with likely back-building cluster action near or east/southeast of Omaha on the edge of the 12 degree 700mb cap towards sunset. I am liking the tornado potential more and more seeing the decent eff shear and strong likelihood of deep moisture pooling on the boundary. A boundary which should be an excellent location for enhanced LL shear to support low level mesos/tornadoes. The cap looks actually good for June (as Mike H was mentioning) to keep things more supercellular Thursday afternoon and possibly early evening. I will certainly be keeping a very watchful eye on how this progresses on later runs....

 

[Brandon Sullivan]

Im targeting somewhere NW of DesMoines.. Not 100 percent sure where... I will ride the bandwagon and be looking for the outflow supercells as well

 

[Scott Lincoln]

Looking at BUFKIT profiles for KDSM, I definitely see some potential for Thursday, but with a few concerns:

The models do not seem to have a firm grasp on the situation. Even the differences between the 00z and the 12z NAM are big. It does seem like the more recent NAM and the GFS are similar, yielding some nicely curving hodographs in the crucial 0-1km level.
The NAM seems to not be as bullish with the dewpoints in the Iowa area, causing some high LFCs and skinnier CAPE in the profile.

After some long drives to South Dakota, North Dakota, and Wyoming only to see nothing, I could sure go for some tornadoes here close to home!

 

[Dustin Wilcox]

My area of interest has once again shifted, this time farther to the West. Per the 0Z 12km I like the area around Platte SD. According to this run a decent tripple point will be in the vicinity by 0Z, I see little reason the models should be overforecasting moisture this time around, with sufficent instability under a 40kt 500mb wave and decent LL backing at the surface and of the LLJ by 0Z the area should be prime for supercell development. I am currently in Yankton SD, probably just stay here for the night and wait for morning to see how different the next model run will be.

 

[Nick Hartley]

I'm starting to think that somewhere along the US Highway 14 corridor is where things are going to pop tomorrow. Targeting from around Pierre to east of Brookings. Might even be a fairly local chase opportunity for me. We'll see what's going on around 11:30 tomorrow morning and evaluate from there. Very favorable conditions it seems like. Best of luck to all who go out tomorrow.

 

[Bill Schintler]

Chase targets for Thursday, June 21

Chase targets:
1. Harrison, SD (10 miles S of Mitchell). Storm initiation: 4 PM CDT.
2. Independence, IA (20 miles E of Waterloo). 5 PM CDT.

Synopsis:
Broad ULVL ridge dominated the WRN half of the CONUS while to the E of this feature a couple of disturbances were diving to the SE over the Upper-Midwest. Severe and slightly elevated storms fired along a quasistationary boundary over MN and WI this afternoon in response to forcing provided by an H5 S/WV. This convection should slowly weaken with the loss of afternoon heating and with the LLJ refocusing further W over the Dakotas. However, it should hold together long enough to push through extreme NERN IA. Further upstream in SD, diurnal convection failed to develop in a highly unstable and nearly uncapped environment NE of a thermal low in SCNTRL SD, probably because of large scale subsidence in the wave of the S/WV as well as an H7 thermal ridge which worked into areas W of the Missouri river. A strengthening LLJ was transporting 16C dewpoints into NEB and SD. Overall model performance was poor with regard to initializing to mesoscale S/WV features in the H5 flow.

Discussion – Nebraska and South Dakota, Thursday:
SFC low-pressure will strengthen over NERN CO, and a boundary extending to the NE of this feature will provide a focus for convection as an H5 vort max approaches WRN SD. Modest shear will couple with very strong buoyancy with observed MLCAPSs to 5000 J/kg. Differential advection of a deep moist layer from the S and very steep lapse rates from the W will further contribute towards unstable EML soundings. Convection should remain capped over most of NEB owing to a stout H7 thermal ridge with observed temperatures of 12-15C.

Discussion – Iowa, Thursday:
Main forecast challenge concerns residual boundaries left over from nocturnal convection. Current thinking is that the small MCS over SERN MN will continue SE while moving into extreme NERN IA and WI. This may serve to push an OFB into ERN IA which should provide a focus for afternoon convection there. Convection should have no trouble firing by late afternoon between US-30 and US-20 owing to relatively cool mid-level temperatures as a couple of compact waves approach and provide forcing along the OFB. A few supercells will be possible along the SRN periphery of the convective complex late in the afternoon, roughly along I-380 between Cedar Rapids and Waterloo, and enhanced hodograph curvatures NE of the OFB along with (250m-6km) shear of 30 kts will support severe potential, with large hail the primary threat with WBZ levels of around 13 kft.

- bill
[FONT=&quot]10:00 PM 06/20/07[/FONT]

 

[Jim Bishop]

This is the first decent looking setup I've seen in a while now. I like South Central to Southeastern Dakota. Conditions look pretty good for supercells and tornadoes along the warm front. The only thing I'd be concerned about are the less than ideal 300mb flow. That will probably keep supercells on the HP variety.

 

[Bob Hartig]

If I could hit the road tomorrow, which I can't, it would be for Sanborn Countyr, SD. (I'm rough at posting images. Hope this works okay.)

 

[Brian Stertz]

Hmmmm....

I had visions of heading north for one last chase before the mean old summer ridge set in. I was a bit leary of HP supercell madness as Jim mentioned in his post. The ETA was doing it's northwest shift thing again, and the LCL's on the 00z run looked a bit too high overall for my liking. I decided to bag it given the very long drive to SC South Dakota and that I have to be in STL by Friday morning. Best of luck to those going out tomorrow.

 

[Van DeWald]

Wow, tough forecast today. Convection is firing along the frontal boundary right now (3 am) across southern ND and northern SD, as well as across southeastern MN. That convection should ultimately push the front a bit further south, along with the subtle short wave moving out of the northern rockies. The models are all over the place regarding initiation, but I'd shoot for an FSD target by 18-21z, with the option of heading north toward Brookings or west towards Chamberlain, all dependent on how far south the front moves. Hi res WRF hitting the northern target harder, 12km Nam hitting the western target. 00z thrrough 06z should definitely be fun. All in all, the best show may end up between KSUX and KFSD and KSFD. Time will tell.

 

[Derek Weston]

Sitting at my parents home in Cedar Rapids.

I'll play whatever moves SE into my region. Hopefully we can get some discrete supercells firing before any large MCSs form. Northern half of the eastern 2/3ds of Iowa seem to have a shot at some of these. We'll see.