These images come from the 18z run of the NAM4KM. I'm not using the 00z run because it wasn't ready when I started assembling these images, and it's pretty much a duplicate of these anyway. The NAM4KM is usually very good at depicting where thunderstorms form, and I've learned to trust it implicitly. It is dead-accurate, in my experience, 75-80% of the time.
Truthfully, this setup is hauntingly similar to the June 22nd scenario we saw in Michigan last year, right down to the time of day. The main difference is that there will be no early day thunderstorms to cool down the environment and thus temper the tornado potential. The first loop represents significant tornado potential throughout the evening. It's going to be off the charts - over 10 in some areas. STP doesn't have to be anywhere near that high to get strong tornadoes - a 4 or 5 would be cause for concern. When you start seeing 10s, you typically start seeing numerous violent tornadoes - EF4s and EF5s.
The second loop is obvious - simulated radar. Nothing short of a nightmare scenario there, especially considering these are forecast to develop after dark.
The third is probably the scariest image. Each one of those swaths represents updraft helicity - that's rotation. Those dark greens are potential tornadoes. Those yellows and reds are potentially violent tornadoes.
I fully expect the SPC to push a high risk with tomorrow's outlook, either first thing in the morning or soon after. The only thing I could see preventing it is if the low level winds are mild. As of the SPC's last outlook, they were forecast to be 15-20kts. However, there's now hints in the latest model run that they'll be on the order of 20-30kts. Surface winds that strong could easily drive a big tornado outbreak.
As with all severe weather scenarios, this one is still a wait-and-see situation right up to the end. I hate the idea of people getting killed tomorrow by these storms. I'm hoping that if an outbreak occurs, it will be one with zero fatalities.
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