Fred Gossage

You mean like this?

Yesterday's runs... while having a very impressive synoptic system... were very forced in a linear fashion for Wednesday. Upward velocities were extremely strong and with a very linear configuration. This, combined with the low-level jet axis being just ahead of the surface boundary on yesterday's runs... restricting the low-level convergence to just ahead of the surface cold front... really screamed a linear storm mode. With this lower amplitude trough configuration, we have trended toward a situation where low-level convergence associated with the western side of the low-level jet is spaced significantly ahead of the surface front... and the upward velocities on the synoptic scale are also more spaced out and subtle. Also, while this won't really back the surface winds toward a southeasterly direction... we're seeing the 850-mb winds trend more SSW to SW, overtop the due south surface winds... which is a more classic configuration for our big tornado days in this part of the country. We often don't see events with a SE sfc flow work out because of the trajectories of the low-level air mass. In fact, all four of Alabama's F5 tornadoes in history happened with surface winds ranging from due S to SW... and an 850-mb flow out of the SSW to SW. While the synoptic system isn't quite as strong on today's model runs... we've stepped away from more of a forced, linear storm mode... and toward more subtle forcing overtop a weakly capped LLJ axis with significant instability. Any veering of the 850-mb jet toward the SSW to SW is going to rapidly ramp up 0-1 km storm relative helicity values... and 0-3 km values are already progged to be sky high. My main concern with Wednesday down here is actually that we may have a little bit of a problem with LCL heights if we reach some of the progged surface temperatures shown in some of the model guidance. Edited for typo.

Just be careful here. Once you get east of the Plains, and especially east of the MS River... into an enviroment that often has deeper boundary layer moisture and is further away from the elevated mixed layer/capping source... these lower amplitude flow events can often be associated with some of our most gruesome tornado events in history. Too much forcing over here, and we either line out or get grungy... very fast. I could go through records and hit you with a VERY long list of dates associated with violent Dixie Alley outbreaks with a less amplied, broader-based trough scenario... and in several cases... a positive tilt configuration.

I can tell you right now that there are many many cases in history.... especially east of the Plains... where numbers like that have supported F3-F5 damage. It's a really bad idea to try to tie EF-Scale to parameter thresholds like that. You can have numbers larger than that.... and other things prevent tornadoes completely.... or have parameters lower than that.... and have F4-F5 damage.

And further south as well... from late morning or midday onward.