6/24/05 FCST: Central/Northern Plains

[Ryan Pfannkuch]

I am curious what others are thinking about the potential along the front sagging southward into eastern NE/western IA Friday afternoon.

With 30kts of westerly 500mb flow and 15-20kts of SW 850mb flow impinging upon the surface boundary, shear profiles look fairly decent although surface winds might be questionable. NAM fcst soundings from today for Sioux City/Storm Lake IA showed pretty decent veering profile.

Severe storms look like a good bet, with the wild card being any possible tornado potential. My main concern at this point are storm mode (all linear?) and possibly high LCL heights. Although I certainly don't expect a very big event, I do think this setup warrants some attention so I thought I'd start the ball rolling.

At this point I'd say generally a few counties on either side of the IA/NE border between SUX and OMA look pretty decent per model EHI bullseyes, with the GFS farthest north and NAM farther south. So much of tomorrow will depend on the evolution of storms forming tonight over the SD/MN area.

Ryan Pfannkuch
Ames, IA
2005 Iowa State Meteorology grad

 

[Scott Lincoln]

Definitely surprised that there wasn't at least one post or so about this on here earlier....

I would say that this bears watching, as the convergence along the front is some of the strongest I have seen forecasted all this season. That could end up being a bad thing though if the cap isn't strong enough to hold off a huge blob of convection.

I definitely see a good instability / shear cross-over in western and northwestern iowa. I dont see the cap as an issue, except that it may be a touch too weak. Convergence is forecasted to be quite enough to form some nice cells....
The LCLs are not fantastic, but appear to get lower as you move westward into western iowa and eastern nebraska.
I myself will be looking for the latest model runs tonight to decide for sure on chasing.

As of right now, based on the convergence and shear and instability, I think the best chances for possible tornadoes would be near Sioux City, IA. then as the evening progresses, I think chances will spread out into western and central iowa as a more isolated threat along the front and the high levels of convergence.

 

[Kurt Hulst]

Well I still like the areas from Norfolk NE to Sioux City IA. Reason being the Winds from 300mb down to 700 actually hold up on the ETA/NAM With sufficient shear. The uncertain factor on this is the weak 850mb shear looked to be around 10 knots SSE at 18z I do like the fact that it is backed at least. But then a little more Veered by 00z. but with the propagation of the convection to the SSE in Central western IA and eastern NE the 850mbs are more southerly.

The NAM estimates a weak CAP around 18z and then strengthens. Is that a possibility of gaining more discrete cells?

The other issue for the mentioned areas is the CAPE is not as high as it is to the west and even the east of those targets. It is doable though. Everything can change with the current convection now popping up in Central Nebraska I’ll be watching outflow boundaries. Good luck to any one that is able to go out tomorrow.

P.S. Pistons are Screwed oh well.

 

[Mike Hollingshead]

Man it kind of sucks, such a close setup and yet such a crappy one. It looks pretty poor to me right now. I may just sit this one out here at home and let whatever comes through come on through. The boundary is still very much capped and the flow along it is quite weak. I suppose the area between Norfolk and Sioux City would be the most appealing to me at the moment, but that isn't saying much(Sioux City and Onawa both backing now). Need to get a meso low to sit there and strengthen around or sw of Columbus. That would get me more excited. Guessing stuff will go up first north of the front out around Burwell.

If this isn't forecasty enough, just send it on over to Talk, as I don't know where the safe place is to post anymore.

Edit: Scratch that. Sioux City is now north of the front with nnw winds and was Onawa ever on a surface plot? I thought it was but don't see it now. Maybe I was looking at Tekama(TQE). If so it isn't backed now either but is veered ssw. CIN eroding over nw IA now along the front. Moisture convergence max is there now as well. Not sure to pay much attention to that at this point or not. Seems like more of a tendancy for the sfc winds to keep veering over there, while flow in se NE down into KS seems to want to stay at least south. Temps starting to climb into the 90s in se NE. I'd still probably want to watch for a meso low there and something to pop ne of it on the boundary, say around Columbus NE.