10/5/07 FCST: IA/NE/ND/SD/MN/WI

[Brandon Sullivan]

What looks like a possibly significant weather event is to unfold on Friday across the upper midwest... Second Season is here...

Discussion: A deepening surface low and associated frontal boundary will lift northward friday afternoon. Convection may be ongoing along the front at that time.. NAM model output generates CAPE values of 1300 J/KG across the area.. Along with a very moist atmosphere.. Throw in the Helicity Values in excess of 500 M2/S2, and the deep layer shear and large hodographs evident in NAM/WRF forecast soundings from Sioux City and Fargo Stations.. Could be an interesting event.. NAM does pick up on a somehwhat impressive temperature inversion (CAP) which does put a fly in the ointment.. But once models can better define the strength of the low, and the CAP, the area will be better defined.. NAM/GFS are hinting at some impressive QPF values along the front. Again, things should begin to define themselves better with time...

 

[Skip Talbot]

This is indeed an interesting looking setup. Several target areas may be in play here with a dryline dropping from the Dakotas into NE and a warm front across MN. Those willing to trek to the northern plains may have a good triple point target where the WRF is maximizing instability and where there is great veering with height in the wind shear. Good mid level flow across the northern portions of the dryline may yield some magic there. With the insane helicity on the warm front, tornadoes may be catchable across MN if the morning junk can clear out and something semi discrete appears. The instability looks rather mediocre at this point, but I must be spoiled from the big Spring setups. I guess this is dependent on whether the morning precip and cloud cover can clear out in time.

 

[Derek Weston]

Could be the best setup we've had in a while. I'm digging the shear and helicity we'll have to work with. Big questions will be the level of instability that can develop as well as how the cap/timing goes. Models currently place the best instability into E SD into W Minnesota. However, the best shear is east into Minnesota.

If I had to pick a location right now, I'd have to say west central Minnesota.

 

[Jim Bishop]

*IF* the cap can break it's tornado central over Northeast South Dakota. It all depends on the timing of a small upper impulse projected to reach the area early in the evening by both the GFS & WRF. The WRF has it arriving a little faster and shows convection firing, the GFS is a little slower and does not fire convection. The thing is if that impulse slows down any it's a cap bust.

 

[afischer]

I'll be watching this one closely since I have the day off tomorrow. Expect plenty of stratus and some elevated convection along the warm frontal zone tomorrow morning in eastern SD. 12Z NAM and 06Z GFS have a pretty hot EML developing into the southern high plains tonight and then riding NNE into the target area by 18-21Z, which appears will be very tough to break through even if the surface heats up into the mid 80s. Progged weak height rises and lack of a strongly convergent warm front also worry me, as does whether the front will be oriented properly. Tonight almost looks more interesting before the intense capping comes out, with some nearly surface-based supercells possible within the LLJ nose in northeast NE.. though deep layer shear looks marginal.

 

[Brandon Lawson]

Is it just me or is the 00z NAM run showing a weaker capping inversion?

 

[cdcollura]

LOL - baby little slight risk in NE Iowa and 2% tornado probs according to SPC ;-(

The models really failed on this one. 2 days ago this was looking like a 9-16-06 event in SD. Not anymore.

Inadequate moisture return, cap, and a weaker-than progged impulse is the culprit.

 

[Scott Weberpal]

My only area of interest at this point is along and perhaps just east of the Mississippi River into Western Wisconsin as the H85 jet noses in between 21z and 00z. Whtether or not these storms develop or will be surface based may become clearer later, but at this point both the RUC and WRF break out precip on the nose of the jet. The environment this far east is still highly sheared, and storms will rotate if they can develop in this environment. It's a long shot, but close to home so I'll be keeping an eye on it.

Edit: The 15z RUC just threw those thoughts out the window.

 

[Mike Hollingshead]

LOL - baby little slight risk in NE Iowa and 2% tornado probs according to SPC ;-(

The models really failed on this one. 2 days ago this was looking like a 9-16-06 event in SD. Not anymore.

Inadequate moisture return, cap, and a weaker-than progged impulse is the culprit.

Not sure it ever looked like 9-16-06 did it? Can't blame the moisture return either, with upper 60s and low 70 dewpoints in eastern NE , western IA heading north.