Severe WX Severe Threat 17-18 March 2021

[warneagle]

A thread for the potential severe weather event this coming Wednesday. I might need to go back and add Thursday since there's some potential for trouble along the east coast before this moves off shore, but for now, the SPC hasn't outlined a threat area so I'll just include 17 March in the thread title.

 

[KevinH]

I live right on the edge of the highlighted area in West Central Georgia. It will be interesting to see if/how these risks areas change in the coming days.

 

[Clancy]

I live right on the edge of the highlighted area in West Central Georgia. It will be interesting to see if/how these risks areas change in the coming days.

SPC is painting a broad area for today and wasn't trying to be too geographically exact. Seeing what the models are suggesting, quite probable the zone expands in the coming days.

 

[Richardjacks]

I think we need to migrate previous posts from the 2021 severe weather thread for forecast/info continuity purposes.

 

[KevinH]

SPC is painting a broad area for today and wasn't trying to be too geographically exact. Seeing what the models are suggesting, quite probable the zone expands in the coming days.

And possibly upgraded to 30% in some areas. For now, at MINIMUM, I say a SLIGHT/ENH risk for Wednesday.

 

[KevinH]

I think we need to migrate previous posts from the 2021 severe weather thread for forecast/info continuity purposes.

I would agree.

 

[tennessee storm chaser]

And possibly upgraded to 30% in some areas. For now, at MINIMUM, I say a SLIGHT/ENH risk for Wednesday.

very quite possible if models hold, you will see a 30 percent zone being introduced by monday at least, and i say that will run from the very far sw tennessee down towards ms and north and central alabama.

 

[Justin Hindman]

While this threat is still a good ways away, models continue to trend for the worse. Could be a day that could get nasty for a big portion of the south east

 

[MichelleH]

The fact that Fred said that Wednesday could be one of THOSE events gives me a sick feeling in the pit of my stomach.

 

[KevinH]

The fact that Fred said that Wednesday could be one of THOSE events gives me a sick feeling in the pit of my stomach.

Keyword: COULD Pray that it does not happen *that* way, but prepare like hell as if it will!

 

[MichelleH]

Keyword: COULD Pray that it does not happen *that* way, but prepare like hell as if it will!

You're preaching to the choir.

 

[warneagle]

SPC is painting a broad area for today and wasn't trying to be too geographically exact. Seeing what the models are suggesting, quite probable the zone expands in the coming days.

Yeah, and I'd expect them to add one for Thursday as well once the models are in better agreement.

 

[jmills]

Tagging along with what Fred said earlier - ~12 of the 15 analogs that CIPS is pulling for this system produced strong/long track tornadoes. The ones that didn't aren't even that close of a match synoptically.

 

[Richardjacks]

I think it is important to look at the beginning of Wednesday's setup. This is today's 12z GFS for Monday 7pm. The zonal/quasi SW flow aloft will give plenty of time for the higher dewpoints to be readily available. Not to mention the low amplitude, far west-reaching flow setting up to the west.

 

[Casuarina Head]

The 12Z GFS flattens the Omega-block axis over the Aleutians late on Wednesday, which leads to downstream impacts vis-à-vis the long-wave pattern, including a deeper low over the Gulf of Alaska and greater shortwave ridging over the Great Lakes. This, in turn, leads to a weaker mid-level feature over the Ozark region vs. the 00Z run, and also leads to a surging cold front that threatens to limit the northward extent of the SIGTOR threat, given that mid-level flow runs more parallel to the boundary along the upper Mississippi Valley (i.e., eastern MO/western IL). This could also undercut the warm sector to some extend and confine the main SIGTOR threat to mesoscale features over eastern MS/north-central AL. 00Z looked more ominous in terms of a lower-amplitude synoptic-scale pattern favouring a wider-scale SIGTOR threat northward to the Ohio Valley. I think that the overall warming of the Pacific basin over the past decade, coupled with recent -AMO trends (weakening AMOC) in the North Atlantic, has made low-amplitude, progressive patterns less likely, even during -ENSO/-PDO setups, hence the dearth of major, widespread tornado outbreaks, for the most part, since 2011–12, especially over the Plains. So events like Palm Sunday 1920/‘65, Super Outbreaks ‘74/‘11, Super Tuesday ‘08, et al. will be harder to come by for the most part, due to AGW being reflected in the absorption of heat and fresh water by the major ocean basins, especially the Pacific and the North Atlantic.

 

[Equus]

And tornado season goes from slow to whoa in the blink of an eye.

 

[CheeselandSkies]

The 12Z GFS flattens the Omega-block axis over the Aleutians late on Wednesday, which leads to downstream impacts vis-à-vis the long-wave pattern, including a deeper low over the Gulf of Alaska and greater shortwave ridging over the Great Lakes. This, in turn, leads to a weaker mid-level feature over the Ozark region vs. the 00Z run, and also leads to a surging cold front that threatens to limit the northward extent of the SIGTOR threat, given that mid-level flow runs more parallel to the boundary along the upper Mississippi Valley (i.e., eastern MO/western IL). This could also undercut the warm sector to some extend and confine the main SIGTOR threat to mesoscale features over eastern MS/north-central AL. 00Z looked more ominous in terms of a lower-amplitude synoptic-scale pattern favouring a wider-scale SIGTOR threat northward to the Ohio Valley. I think that the overall warming of the Pacific basin over the past decade, coupled with recent -AMO trends (weakening AMOC) in the North Atlantic, has made low-amplitude, progressive patterns less likely, even during -ENSO/-PDO setups, hence the dearth of major, widespread tornado outbreaks, for the most part, since 2011–12, especially over the Plains. So events like Palm Sunday 1920/‘65, Super Outbreaks ‘74/‘11, Super Tuesday ‘08, et al. will be harder to come by for the most part, due to AGW being reflected in the absorption of heat and fresh water by the major ocean basins, especially the Pacific and the North Atlantic.

I'll reserve judgement on next Wednesday until it gets closer, but I've observed the phenomenon you're talking about. For example, the last three Marches have brought the Jacksonville (AL), Beauregard-Smith's Station, and Nashville-Cookville tornado events. All very significant and destructive to be sure, but in each case it was really only one cell that was able to go gangbusters on the day.

If this is climate-change related (which I suspect you are correct that it is), it just seems surprising that it occurred so abruptly and so thoroughly, like the flip of a switch. I mean, I could see it as a general trend over time, but every system, every spring for the last almost-decade? Especially coming right after 2011.

 

[Clancy]

The performance of severe setups post-2011 has certainly been mixed, though this upcoming threat certainly doesn't seem like one to sleep on, regardless.

 

[pohnpei]

The 12Z GFS flattens the Omega-block axis over the Aleutians late on Wednesday, which leads to downstream impacts vis-à-vis the long-wave pattern, including a deeper low over the Gulf of Alaska and greater shortwave ridging over the Great Lakes. This, in turn, leads to a weaker mid-level feature over the Ozark region vs. the 00Z run, and also leads to a surging cold front that threatens to limit the northward extent of the SIGTOR threat, given that mid-level flow runs more parallel to the boundary along the upper Mississippi Valley (i.e., eastern MO/western IL). This could also undercut the warm sector to some extend and confine the main SIGTOR threat to mesoscale features over eastern MS/north-central AL. 00Z looked more ominous in terms of a lower-amplitude synoptic-scale pattern favouring a wider-scale SIGTOR threat northward to the Ohio Valley. I think that the overall warming of the Pacific basin over the past decade, coupled with recent -AMO trends (weakening AMOC) in the North Atlantic, has made low-amplitude, progressive patterns less likely, even during -ENSO/-PDO setups, hence the dearth of major, widespread tornado outbreaks, for the most part, since 2011–12, especially over the Plains. So events like Palm Sunday 1920/‘65, Super Outbreaks ‘74/‘11, Super Tuesday ‘08, et al. will be harder to come by for the most part, due to AGW being reflected in the absorption of heat and fresh water by the major ocean basins, especially the Pacific and the North Atlantic.

The effect of global warming on tornado activity was complicated. Much warmer Pacific Basin indeed but much warmer Gulf Of Mexico also, which can bring more moisture to the land when there is a system.

 

[KevinH]

The performance of severe setups post-2011 has certainly been mixed, though this upcoming threat certainly doesn't seem like one to sleep on, regardless.

If this ends up being an overnight event I won’t be sleeping anyway.