And we can already see the GFS is falsely decoupling the boundary layer much like it did with this past event resulting in only a few hundred joules of CAPE. NAM has a more realistic handle on surface temps, although it's likely underestimating moisture return (again, just like it did with this past system at this range).
Here's the deal about the instability- there is alot of dry cool air that has been pushed south behind Sunday's system all the way into the Gulf. A return flow from the Gulf is expected later tomorrow into Wednesday. While I am not sure we will see dewpoints near 70°, they will at least be in the low 60's for western sections by Thursday afternoon...some models suggest they will barely make it to the mid 50's...and are probably underplaying this a bit.
Latest run of the NAM moves a powerful line of thunderstorms through Mississippi and Alabama Thursday afternoon/evening despite limited moisture return and instability (which are probably underdone as noted in previous posts). This could absolutely be a significant event if even more instability is realized.
I know we're still 3 days out, but I really am not seeing a significant tornado threat across Dixie Thursday. Pretty substantial damaging wind risk, but it seems way too messy with too many caveats for a significant tornado threat to materialize across MS/AL/LA. Maybe a decent QLCS tornado threat however. Now that I have said this, watch an outbreak occur.
So I'm leaning more towards a QLCS type situation for Dixie Alley, but looking at the 500mb vorticity map off the GFS, I notice some local maxima in Alabama ahead of what would appear to be the main line. Question: would those possibly be supercells ahead of the line?
I still think the models are downplaying the amount of instability for Thursday/Thursday night. I do think the instability will be lower than we originally thought. It will be interesting to see where a secondary low forms. Models are showing that as a solution, but they vary on placement and intensity. It will be key on who sees the worst weather. Damaging winds will definitely be the biggest threat with spin-up tornadoes possible along the main line.
Very important AFD particulars to be monitored from BMX:
This will be a very dynamic system with 110kts of meridional upper-level flow developing,
75kts at 500mb, 65 kts at 700mb, and 50-60kts at 850mb. At the
surface, low pressure centered over the Great Lakes associated
with the northern stream trough will be the main feature with a
cold front extending southward. But the amplifying trough
interacting with the cold front along with potential convective
processes will result in a potential secondary surface low
developing. This will be an important feature for the evolution of
the severe threat. The ECMWF is most concerning with a 998mb low
tracking along the Highway 278 corridor but other guidance is
weaker or further north with the track of this secondary surface
Now models are picking up on a secondary low pressure (a strong one at that) moving from Northern MS into TN/KY later Thursday. This will enhance the severe wx threat in MS/AL although I’m unsure that storm mode will cooperate for a higher end tornado threat. This will likely be a nasty damaging wind/secondary tornado threat.