2024-04-27 EVENT: TX/OK/KS/MO/IA

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Following an impressive but questionably timed synoptic wave on Thu-Fri, a slightly more compact shortwave is forecast to eject into the southern Plains sometime on Saturday. Given how closely spaced these two systems are, there is still considerable uncertainty regarding all aspects of the second wave (timing, geometry, etc.) -- more so than is perhaps typical at 120-h lead time these days.

Despite a somewhat wide envelope of NWP solutions right now, I would still say Saturday looks like the most slam dunk tornado setup for the Plains (not necessarily nationally, though) out of the upcoming sequence late this week into the weekend. Although diurnal timing may once again be less than ideal, in this case it's more on the early side: there's a fairly widespread signal for CI by 18z over portions of OK and/or N TX.

However, to my eye, the potential messiness and early CI of this setup calls into question its chaseability more than its capacity to produce tornado reports. Most guidance currently depicts a compact, negative-tilt shortwave with 60-kt SW flow streaking over a warm sector with a 40-50 kt LLJ by early evening. Unless the overall synoptic evolution changes considerably, at least a handful of tornadoes are virtually guaranteed with that type of setup in late April, whether they're highly visible or not.

From a chasing perspective, I can imagine something vaguely reminiscent of a day like the 2015-05-16 Elmer, OK, event. That is not to say that such an intense, long-lived tornado is guaranteed; I'm talking more about the early, widespread CI, requiring patience and finding the needle in the haystack among lots of junky ongoing storms elsewhere along the dryline. To me, that scenario is sort of the middle ground right now: I can also imagine morning convection being so detrimental that it really kneecaps the whole setup at one extreme, all the way up to and including a significant regional tornado outbreak if the timing slows down and early convection is less problematic than the current median solution (the GDPS, and perhaps UKMET, are closer to this right now).
 
The great thing about Saturday is all kinds of outflow boundaries will be around. Surface will be a target rich environment.

Upper levels check out at this time, Tuesday looking at Saturday. I don't have much to add. Just want to agree Saturday should be a good chase day.
 
Finally really looked this over tonight on the 00Z GFS and it sure does look like a big outbreak. Pretty much can only get worse in further runs or we're going to have some incredible footage. Timing of the wave is perfect and the shape of the trough is that ski jump shape. Moisture is rich and a deepening 994mb low over sw kansas. Will be interested to see how the NAM picks things up tomorrow. Could be looking at a very busy day Saturday.
 
It has been years since I've had a "feeling of impending doom" about a severe weather situation but I have one for Saturday.

And, I had that feeling before I saw the attached combined tornado/hail/wind forecast. What I believe it is indicating is a high risk of tornados in the SPC forecast area and giant hail toward KC on the other side of the warm front.

Whatever the details, I'm very worried about Saturday.

If I were going to pick a target now, it would be Wichita.
 

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At the moment the NAM has some crazy forecast soundings at 0000z from Salina to Concordia coincident with a shortwave and left exit of the jet streak. These next few days are gonna be interesting if things verify with these big numbers.
 

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Long time no post, but I wanted to make a forecast here for my local target area. I won't be out and about the plains this weekend, and have some training for work on Saturday until about 4pm, so I am restricted to the IL/WI/IA border areas. It seems there is a risk for some frontal/prefrontal storms Saturday evening in a favorable environment, the caveat being nebulous forcing and height rises. SPC currently has the area in a slight risk and mentions all hazards across this area. Rather than just pluck soundings I wanted to see if others agree with my assessment.

Upper air: A departing 500mb trough from Friday will leave slight height rises behind on Saturday as it moves off to the Northeast, with another developing upper low across Western Kansas. Upper winds remain strong across the area, but heights slowly rise on Saturday. Euro has it at about .5 DAM/hour, and I and dumb enough to admit I don't really know if that is significant enough to cause subsidence/be hostile to storm development or not, so if anyone wants to chime in, go for it. 500h_change_012h.us_mw.png

Despite this, many models show convection across the frontal area. And the MPAS ensemble has almost every member firing storms along AND ahead of the front in IA/IL, in what I can only assume is a surface convergence zone/prefrontal trough (are they the same thing? I never really knew what constituted a surface trough).
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Are these prefrontal storms firing simply due to the convergence and a breakable cap with a favorable environment for supercells? Euro convects, GFS does not and NAM is run to run. Those that do tend to show some storms forming by/at 0z, at the very least along the front. I posted the most recent NAM sounding below and confirmed the RFFS has quite a similar environment proved. What I can't pinpoint is if there is actually any kind of shortwave moving along the upper trough axis that will aid in storm development. Feel free to add input or corrections to my forecast. I hope I can get a nice discrete supercell out of this, perhaps a tornado if this environment is realized. I really like almost everything about this sounding.
2024042512_NAM_060_41.71,-90.86_severe_ml.png
 

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While there looks to be plenty of good targets at this point, I'm still liking NC Kansas as a high risk/reward scenario. There's agreement in guidance of a cell going up near the triple point with a good mix of parameters. DPs are in the low 50s on some models, and there's a risk of convection crossing the warm front early on, but I'm hoping the WF resolves further north come Sat, or the cells can latch onto the boundary.

To Brian's point, the HRRR has some leading cell going into WC Illinois with strong echo tops around 23z, but the instability and helicity seem to bottom out shortly afterwards... not sure what to make of that quite yet.
 
Am I crazy in seeing some potential downsides to tomorrow from a chasing perspective? There will no doubt be tornados, but will there be discrete storms, or will this be like one of those Dixie Alley outbreaks with clusters and embedded mesos? I admit I'm not the best forecaster (especially considering how long I've been doing this!) and I don't always have the ability to articulate my thinking in the proper technical way, but based on pattern recognition I feel like this is one of those days that stuff blows up everywhere, storms move fast, and it's a frustrating chase day. This could very well just be my personal bias as I deeply regret being unable to chase this, and if I were out there of course I would! But here are some of the things that concern me... I'm putting these out there more to learn and be proven wrong!

- The Euro, at least on last night's 0Z run (today's 12Z not available yet) does not wrap 60s dews into the triple-point. As a result, backed winds and the best directional shear is not co-located with the best moisture. Even the NAM3K has a similar look - the best moisture just not quite making it to the triple point
- Plenty of speed shear regardless, but there is a meridional component to the mid/upper flow
- Flow parallel instead of orthogonal to the dryline
- As a result, storms may move rapidly to the cool side of the front?
- As in previous events, convergence lacking further south along the dryline
- Open warm sector development appears a possibility; hard to target
- Surprising lack of modeled precip along the dryline, but plenty to the east in the open warm sector

Not hard to get TOR and PDS TOR soundings, and I'm sure there will be plenty of tornados, I'm thinking more about chase quality and ability to target with precision. There is always more downside to a setup like this. Of course you can all tell me I'm just a crazy, cantankerous old man trying to make himself feel better about not chasing LOL

(Edited to add point about flow orientation relative to dryline)
 
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I'm waiting to see the next SPC update here in a little bit, to see where they put the slight risk at.... I'm right on the border of it for tomorrow so that will be interesting to see. Since we now have cloud cover with precipitation starting to advance on the Chicago metro area.... I do not expect it to get quite as warm today as forecast and thinking that may have an impact on tomorrow. Have a feeling I will be out though as the slight risk at current time is just barely to my west and north.
 
Am I crazy in seeing some potential downsides to tomorrow from a chasing perspective? There will no doubt be tornados, but will there be discrete storms, or will this be like one of those Dixie Alley outbreaks with clusters and embedded mesos? I admit I'm not the best forecaster (especially considering how long I've been doing this!) and I don't always have the ability to articulate my thinking in the proper technical way, but based on pattern recognition I feel like this is one of those days that stuff blows up everywhere, storms move fast, and it's a frustrating chase day. This could very well just be my personal bias as I deeply regret being unable to chase this, and if I were out there of course I would! But here are some of the things that concern me... I'm putting these out there more to learn and be proven wrong!

- The Euro, at least on last night's 0Z run (today's 12Z not available yet) does not wrap 60s dews into the triple-point. As a result, backed winds and the best directional shear is not co-located with the best moisture. Even the NAM3K has a similar look - the best moisture just not quite making it to the triple point
- Plenty of speed shear regardless, but there is a meridional component to the mid/upper flow
- As a result, storms may move rapidly to the cool side of the front?
- As in previous events, convergence lacking further south along the dryline
- Open warm sector development appears a possibility; hard to target
- Surprising lack of modeled precip along the dryline, but plenty to the east in the open warm sector

Not hard to get TOR and PDS TOR soundings, and I'm sure there will be plenty of tornados, I'm thinking more about chase quality and ability to target with precision. There is always more downside to a setup like this. Of course you can all tell me I'm just a crazy, cantankerous old man trying to make himself feel better about not chasing LOL
I don't think you're crazy at all. I'm getting concerned about messy storm modes and a lack of truly discrete cells as well. I'm off tomorrow and live in OK, so I'll definitely be chasing, but I don't really have much of an appetite for tangling with an HP mess. Hopefully a discrete storm mode will hold out longer than some models are suggesting. Even the latest SPC outlook notes that the question mark around storm mode is what is preventing them from introducing higher tornado and hail probabilities. I'm also concerned about safety. The potential for hoards of chasers mixed with messy storm modes and a very high ceiling parameter space could lead to trouble.
 
Here is my forecast: Tornado Forecast for Saturday, April 27 and I've included a special discussion for chasers and meteorologist. I'm going "high risk" on my 4-point scale. I disagree with SPC that earlier rain is a deal-breaker.

Given the fast bias, I've moved everything a bit to the west than I otherwise would.

I do agree that storms will be moving rapidly ~40 mph per AccuWeather's tool.

Good luck!!!
 
I agree with the concerns about storm mode and timing. The 12/18z CAMs are depicting a mostly uncapped environment leading up to the main event, and storm motion in some models is close to parallel to the forcing gradient, so messy mode and/or early transition to linear seems quite likely. There's a lot that could go wrong with timing too, with earlier storms forming beneath an uncapped environment before low-level shear parameters are maximized. That said, CAMs seem really all over the map to me for this event being so soon - some CAMs are quite aggressive in airmass recovery in wake of earlier storms, some CAMs like NAM barely initiate anything prior to the main event.
 
New NAM is rolling in. I was able to cherry pick the best sounding ever.

2024042700_NAM_024_36.02,-96.31_severe_ml.png
 
For all the concerns I am seeing here and elsewhere about messy storm mode and too many storms, I am beginning to have the opposite concern - quite a few of the CAMs available so far this evening are showing no storms at all along the dryline tomorrow. Not all, but several. Models do seem to be in pretty good agreement on dryline placement, from around Dodge City southward to the eastern edge of the Panhandles. If things stay as they look now, I will probably start out somewhere around Greensburg, but not overly confident right now on actually getting dryline storms. Staying in Dodge City tonight. I sat out today because at 74, driving from western KS to Omaha or Iowa and then back again was just too much. Of course since I did not chase today, that ensured there were tons of tornadoes in today's target area. Those of you who saw them, you're welcome, LOL!
 
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