Alright, I'm obsessed. I just spent the last 6 hours staring at model data (yes and even GFS), satellite and observations.

Summary:

- Early T-Storms/Severe/small chance for tornadoes in ND
- 4-6pm development near Leola, SD, but threat for strong capping may mean bust or elevated cells.
- 4-6pm eroded cap in SW/SC MN should mean surface based supercells and tornadoes in Montevideo to New Ulm and Mankato and Owatonna vicinity.

Discussion:

I'm very confident in my feelings, but capping may be a concern farther west so I'm adjusting my primary target into Minnesota.

First off, model performance... I think the NAM is running a little too strong with the low, temperatures are a little too warm at the surface, and too cool aloft. In particular 700 temps and 850 temps are running about 2-3 degrees c too cool. Which is not good news. Jet speeds seem a little fast, but placement of the low is alright.

GFS is a little better, low is still a little strong, and temps are a hair too warm, but only by about a degree or so.

The good news is that although the forecast period has very high CIN values and very warm temps, and the NAM seems to be a little cool to begin with, the GFS has a better initialization and the forecast period for tomorrow has it a bit cooler by a fair scale.

So, if this is correct, and dew points are ok on NAM from what I can tell, the too cool aloft and too warm surface would mean that the CIN values are too high in NAM.

So what this suggests to me is that NAM may actually be overdoing the capping, despite currently being too cool.

With very slow storm motion and fairly strong surface inflow winds for this time of year, excellent shear aloft, I think this could be a spectacular day for viewing tornadoes.

Now for the details...

Early morning showers and thunderstorms in Western North Dakota should be the start of it. They will likely remain below severe limits until early afternoon across southwest to north-central North Dakota where large scale ascent would help to get this blob of showers and storms to get a few elevated hailers. Eventually these storms will get surface based and pose a slight tornado threat, however storm mode, low helicity, questionable deep layer shear, and declining MLCAPE values should limit the tornado threat in North Dakota.

Once this blob of showers and severe storms moves east enough to interact with the areas that have been getting sun all day (Eastern SD for example) new development should fire ahead of the propagating complex. I could see a severe storm popping up near Leola, SD, which may initially be elevated, but with any luck may become rooted in the surface. If this occurs, its location on the triple point with the Inverted Trough and stationary boundary should be enough to give it a full life cycle, including tornadoes.

However, I think a better, safer bet may be had by going with the areas where CIN shouldn't be so much of a problem.

Normally the classic position of being in front of the low, at the triple point, etc. would be my first pick for chasing, but I think I'm actually going to go with the center of the SPC risk. Smack dab in the middle of their tornado threat may indeed be the best place to be for chasers in this scenario... and here's why I think that:

The problem with the western stuff is the cap, and ongoing convection to the northwest. The stuff coming east out of North Dakota is probably going to suck up anything that develops in front of it and line things out in response to the shortwave. On top of that, the stuff that may develop ahead of the junk may have a hard time getting surface rooted with a strong cap. Sure good forcing will likely help to develop severe storms ahead of the crap around the triple point (say Leola, SD area NW of Aberdeen) but the capping question is one that makes me wonder if that's going to be my best gamble.

The alternative is in the SPC's primary risk area where you are well separated from the low, but still on a good boundary. The stationary boundary area in SW and SC Minnesota may prove to be the most active if enough sunshine can get in. You won't get good forcing from a point source like a low pressure center, and the shortwave will pop things up to the west, but along this boundary you may have true surface based convection to get things started with sunshine eroding the cap.

This is a positive for chasers on a couple levels... One it's less of a question of busting if you're targeting the area where the CIN is forecasted to erode completely, and secondly, you really do have a better chance for tornadoes with these storms without question if they are surface based.

You are farther separated from the large scale ascent and synoptic circulation so storm motion should be just drifting easterly or nearly stationary, certainly keeping storms rooted onto this strong boundary.

It's still going to be a tricky one because of capping, and proper amounts of forcing, but I feel quite confident in my target of New Ulm, MN between 4-6 p.m., with a secondary target of Leola, SD in the same time period.

The task in the morning will be to make the final decision based on the following factors:
- Positions of surface features (still in line with guidance?)
- Satellite (will MN see sun all day?)
- RUC progs on cap eroding in both places

Andrew Revering
Convective Development, Inc.
http://www.convectivedevelopment.com/