I would beg to differ. Straight south surface winds can cause the same issues. It can cause failure modes such as storms just not getting enough shear to produce and causing any tornadoes that do produce to be shorter lived and not to be long track monsters…This would be good news. SSW surface winds produced the two largest outbreaks that we have on record. The straight south winds could still bring some of that dry air in and cause these failure issues. Again if this is incorrect please correct me.
With respect, let this post officially count you as standing corrected. If you think due south surface winds would potentially cause issues with not enough shear (which is incorrect, and hundreds of people have died here over the years to prove it incorrect), then a south-southwest surface wind definitely wouldn't be more favorable in that respect. Dewpoints to the due south of Alabama will be in the upper 60s to lower 70s over the Gulf. The problem with southeasterly surface winds on a synoptic scale here is once you start introducing a bit of an easterly component to that, you're not advecting from the Gulf anymore. You're advecting from Georgia and South Carolina.
Total respect. I wanted to be corrected if I was off base.
The reason why more strongly backed low-level winds are so important in the Plains is the same reason they are actually a hindrance here unless it's on the small-scale near the storms... low-level trajectories. Out in Oklahoma and adjacent areas, if you're advecting from the southeast, you're advecting from the western half of the Gulf of Mexico. You get winds veer any more than beyond due south, and you're starting to bring in drier low-level air from the southwest. You're also lessening low-level convergence along the dryline in an environment that climatologically has stronger capping than Dixie Alley because of its proximity to the EML source region versus us and our direct proximity to the boundary layer moisture source versus them. Unless we get the infrequent strong EML plume overtop our warm sector over here, it usually takes less forcing to initiate storms versus what it usually does out in the Plains. That's also why, generally speaking, sharper troughs are often needed out there whereas sharper troughs often produce messy storm modes over here.
Makes total sense. I appreciate the explanation. I just had the thought the southerly component of the winds could draw some of the drier air from the eastern gulf into the storm. Sounds like that is only an issue with a SSE component to the winds.
Just to add on to what Fred said with a bit more abstract look…
And to further add to all of this correct information above, vertical turning from due S or subtly SSE at the surface to SSW at 850mb to SW at 700mb has been plenty enough directional shear for a very large percentage of the (E)F4-F5 events in Dixie Alley over the years. The speed shear aspect of the vertical wind profile will carry a lot of the weight for storm-relative helicity and streamwise vorticity as long as there is some degree of clockwise turning with height.
You noticed that too? Things either fizzle out or congeal into a QLCS by the time they get here.
Neat?!
Yeah I see it too. It extends up into TN as well
wonder how and if that would have a effect on the severe weather potential ….. less convection means no messy storm mode ?
