The image above is a calibrated probability of severe thunderstorms from the SPC SREF. I think it approximately outlines the area with the highest risk Tuesday the best. This NW to SE axis is where a warm front will likely set up Tuesday afternoon into the evening hours. While there is impressive wind shear and strong instability forecast to be in place, it’s not a completely easy forecast.
The most likely scenario in my mind is that a few (2-4) supercells fire up by mid afternoon near the warm front in central Nebraska and quickly go tornado-warned. Any of those cells could be monsters and drop a strong (EF-2 or stronger) tornado. With the atmosphere that’s in place, these tornadoes could either stay on the ground continuously for quite some time, or at least cycle, touching down multiple times. Some other cells may also fire, but the greatest focus could potentially just be on those cells along the warm front.
What are the wild cards? Well, just because the atmosphere is primed and severe weather parameters are forecast to be off the charts does not necessarily mean this will be a widespread tornado outbreak. It could be a very isolated event with just a couple of tornadoes, but even if that happens, any tornado could be particularly dangerous/damaging. It’s fairly clear that the tornado focal point will be the warm front, but further northwest near the triple point is another area to watch. Does a cell fire near there and blow up like crazy, or do the further east cells dominate the action? It’s less likely, but a few supercells could also fire up in the warm sector near the Kansas border, but with higher LCLs, it may be tougher to drop tornadoes down there. Then yet another question is how far north will the warm front go? These are all things that should become more clear into the morning hours on Tuesday.
The tornado “event” is targeted from mid-afternoon (3-4 p.m. or later) through the first part of the evening (10 p.m. to midnight). After that, the storms will likely merge into a powerhouse bow echo. There is a possibility that we could even be dealing with a derecho overnight into Iowa, Missouri and perhaps Illinois, so widespread damaging winds will probably affect more people than a few tornadoes might. (The chaser focus is more on the tornadoes than the bow echo/derecho situation, but with the latter occurring at night, that could be a real messy scenario) Even into the early Wednesday morning hours, large hail and isolated tornadoes cannot be ruled out.
Wednesday is beyond the scope of this post right now, but after morning storms there could be a lull in the action. Another round of potentially significant severe storms could fire later in the day, but there are still details that need to be worked out there.
From here on out, it’s going to be more about the actual trends and observations, with just a bit of help from the high resolution near-term computer models.
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