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Severe WX March 3rd-5th 2025 Severe Weather Threat

ashtonlemleywx said:
So is the current thinking that the GFS, Euro, and NAM are having early season moisture bias? The big debate in my storm chasing circles at the moment is the Northern extent of the instability and warm sector.
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I'm not confident that instability doesn't struggle, but with strong wind fields, I don't think AL gets through this without a number of QLCS tornadoes.
 
ashtonlemleywx said:
This is what I've been telling everyone. We've just seen this happen so many times in the past. They underestimate moisture return/daytime heating and then BAM cape values explode once in cam range.
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The trend I've seen several times is:
1) Instability goes up, especially for the daytime areas, as we approach close-range
2) By the morning of, realized instability is higher than modelled
3) As the afternoon comes, SBCAPE values are progged to decrease in the evening on modelling
4) We get a brief decrease in diurnal heating after dark
5) Strengthening LLJ bolsters moisture return as storms get into AL
 
Clancy said:
The trend I've seen several times is:
1) Instability goes up, especially for the daytime areas, as we approach close-range
2) By the morning of, realized instability is higher than modelled
3) As the afternoon comes, SBCAPE values are progged to decrease in the evening on modelling
4) We get a brief decrease in diurnal heating after dark
5) Strengthening LLJ bolsters moisture return as storms get into AL
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Plus that shorter distance to the Gulf coastline in Eastern MS going into Alabama helps moisture and usually isn't factored into the modeling.
 
The specific values of low-level moisture and instability within where the warm sector ends up being located are likely getting underdone, but the idea of the warm sector getting increasingly pinched as the system heads east is a real one, and it is a synoptic level problem that is not only not trying to change, but is getting more prominent as we get closer. The upper wave is coming out a bit too amplified and meridional, and this effect on the downstream wavelengths is causing the low-level winds east of the Mississippi River to have too much of an easterly component to get good moisture advection. This isn't Oklahoma. The deeper low-level moisture comes from the western and central portion of the Gulf, which is not located to our southeast. Synoptic level southeast flow is not favorable for robust low-level moisture advection east of the Plains. That's why the vast majority of our larger tornado events here in Dixie have a due south surface wind on the synoptic scale and most Plains chasers ahead of time think low-level shear isn't optimal, only to be proven wrong. The warm sector will get increasingly pinched as you head east of I-55. But yes, within the warm sector itself, dewpoints and CAPE values like to trend upward some as we get closer.
 
Clancy said:
NAM underdoing moisture return at 11 AM the morning of an event.
View attachment 34267
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Fred Gossage said:
The specific values of low-level moisture and instability within where the warm sector ends up being located are likely getting underdone, but the idea of the warm sector getting increasingly pinched as the system heads east is a real one, and it is a synoptic level problem that is not only not trying to change, but is getting more prominent as we get closer. The upper wave is coming out a bit too amplified and meridional, and this effect on the downstream wavelengths is causing the low-level winds east of the Mississippi River to have too much of an easterly component to get good moisture advection. This isn't Oklahoma. The deeper low-level moisture comes from the western and central portion of the Gulf, which is not located to our southeast. Synoptic level southeast flow is not favorable for robust low-level moisture advection east of the Plains. That's why the vast majority of our larger tornado events here in Dixie have a due south surface wind on the synoptic scale and most Plains chasers ahead of time think low-level shear isn't optimal, only to be proven wrong. The warm sector will get increasingly pinched as you head east of I-55. But yes, within the warm sector itself, dewpoints and CAPE values like to trend upward some as we get closer.
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Quick question Fred , Are some our bigger tornado events occurred with a surface wind out of the southeast ? Vs south
 
tennessee storm chaser said:
Quick question Fred , Are some our bigger tornado events occurred with a surface wind out of the southeast ? Vs south
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It was already answered in the post you're responding to. The statement that answers the question for you is what prompted you to ask the question that's already answered. :)
 
12Z CIPS analog guidance really favors southern MS for severe, especially tornadic, activity. Generally coincides with what the 12Z GFS advertised, with southern MS and northern LA during the late afternoon and evening having the best overlap of diurnally-based instability and kinematics, which will probably be rapidly intensifying around then.
1740775926130.png1740775938135.png
 
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