2025-03-19 EVENT: IL/IN/KY/TN

[Andy Wehrle]

Was surprised by the lack of any mention of a tornado threat on yesterday's initial Day-2 outlook given the depiction of robust 3CAPE amid strong shear and doable LCLs on the HRRR and to a lesser extent, other CAMS.

With the HRRR remaining consistent and the RAP also on board, SPC has jumped directly from 2% on the second Day-2 outlook to a 10% hatched significant tornado outlook for portions of central and northern Illinois, so I think today is thread-worthy.

Currently looking at targeting somewhere in the Ottawa-Pontiac-Bloomington area.

 

[William Monfredo]

These types of spring setups can be very photogenic.
A low-topped environment like this might produce beautiful "bonsai trees of the storm world."
Equilibrium Level below 30k ft., perhaps some clearing, steep lapse rates developing...dust off the camera.

 

[Andy Wehrle]

Of course, now the HRRR has dramatically backed off its ominous runs from just a few hours ago. Seems the dewpoints will verify on the lower end after all. Still might be a photogenic mini-supercell or two.

 

[Dan Robinson]

Seems like a fairly obvious classic play today in the northern half of the arc of convection. Though I am thinking the southern half may perform as well as the jet noses in along the IL/IN border. The problem in that area is that some models (GFS and RAP) are painting a slight inversion just above the surface. I'm not sure what to make of that. CAMs aren't as aggressive with UH in the southern areas, though as we know, that doesn't mean much in this type of environment. As for moisture, the 50F line is already at I-64, so I think we'll at least have that much by storm time.

No such thing as a sleeper Midwest setup any more, I'm seeing posts by chasers flying in from across the country to chase this one.

 

[Andy Wehrle]

Yeah, now looking like maybe a little further north might be better, where the moisture pools a bit and gets pulled back west in slightly more backed flow right along the warm front. Would shrink the risk area compared to earlier, but may work out in my favor since it's closer.

 

[Dan Robinson]

Current sky looking west from New Baden, IL (STL metro) at 9:15am:



Something I did not see coming at all was the dust plume from the southwest. Satellite shows we're in the clear cloud-wise, but the dust plume is thicker than a sold cirrostratus deck over us here now. Unless that clears out soon, it will severely hinder insolation until very late today for the entire risk area. Not much of a clear gap between that and the incipient convection.

https://twitter.com/x/status/1902361369392865770

 

[Andy Wehrle]

Will be a big hindrance for viewing what I thought were gonna be crisp, clear low-topped updrafts. May sit this one out for that reason alone.

 

[Jeff House]

Yeah that dust wastes a good day where structure will be crisp over ideal terrain. Morning rain will only serve up an outflow boundary in Illinois. Missouri cells can amp up in Illinois when they reach the said boundary in the afternoon. Might even get the ol' Iowa surprise first.

Upper winds don't offer a wide turn from 850-500 mb but it's enough in this situation along a WF or more likely outflow boundary. Right where those low level winds back, and where SRH is greater, today should produce. Will anyone see it? Ask the dust!

 

[Andy Wehrle]

Actually a decent patch of clearing (including [lack of] dust) seems to be working its way into WC IL at the moment.

Wouldn't be the morning of a chase day without a few headscratchers from the atmosphere, I guess.

 

[Jesse Risley]

I think the moisture is going to end up on the lower end of the threshold otherwise this could be similar to December 01, 2018 although displaced a bit further to the northeast. I'm curious as to how ongoing convection in the best risk area will affect instability although I suspect a tornado or two will occur across the open warm sector in EC IL or far W IN although, synoptically, I'm inclined to favor the triple point sector just east of the DL bulge which appears to favor NW IL after 21z particularly east of Moline towards Rockford perhaps somewhere north of I-80 or south of I-88. Models seem to continue to favor this region for a triangular juxtaposition of the best shear and modest 0-3 km CAPE parameters before sunset. I wouldn't even be surprised to see an initial tornado report or two along or just west of the Mississippi River from northwest of Burlington to west of DVN if initial storms track up that way before crossing the river. If we had deeper moisture and broader clearing this would definitely be a higher-end event all other things considered. I can't see the dust impacting instability as much as it would visibility, as the extent of any clearing and depth and quality of moisture return tend to dictate how substantial these events can be. This is a true cold core setup as well with H5 temps <-20C across eastern Iowa so for those what want to focus on the cold core storms as opposed to those across the traditional open warm sector lower-50s dews along a tongue to steep lapse rates feeding into the low have historically produced tornadoes in this region all other parameters being favorable.

 

[Jesse Risley]

Seems like a fairly obvious classic play today in the northern half of the arc of convection. Though I am thinking the southern half may perform as well as the jet noses in along the IL/IN border. The problem in that area is that some models (GFS and RAP) are painting a slight inversion just above the surface. I'm not sure what to make of that. CAMs aren't as aggressive with UH in the southern areas, though as we know, that doesn't mean much in this type of environment. As for moisture, the 50F line is already at I-64, so I think we'll at least have that much by storm time.

No such thing as a sleeper Midwest setup any more, I'm seeing posts by chasers flying in from across the country to chase this one.

I could end up being wrong due to the dynamic nature of the system but just looping the surface map here the last few hours the deepest moisture is still south of I-64 down in far S IL so to me the best bet for that to reach either of the two best target areas would favor the E IL/W IN target across the southern portions of the more open warm sector where traditional supercells would be most likely. I don't see that moisture getting up closer to the I-80 or I-88 corridors later which means the tor threat there or in the cold core sector back further west looks to be much more modulated only owing to lack of a better dewpoint influx for that target area.

 

[Dan Robinson]

Current sky at New Baden (STL) at 1:00PM:



Marked improvement, though a lot of dust lingering in the lowest 1-2km. I've been leaning on secondary-targeting this thing all day, and I'm now past my decision time to make it to the primary (northern) one. Heading up to Effingham and will hedge north toward I-74. I'm not counting out the I-64 corridor either. A real possibility they will see 60F dewpoints by 22-23Z, so something producing there would not surprise me. It would be preferable in terms of terrain (providing it happens west of the Hoosier National Forest) and of course a much shorter drive.

 

[Jesse Risley]

0-3 km shear vectors are oriented parallel to the boundary across the northern risk area into central and NC IL which likely yielded the more QLCS nature of that convection ahead of the dryline, which blew through here (WC IL) in the last 30 min or so and it's windy! SRH improves markedly this evening across EC IL into WC IN where the best moisture lies juxtaposed with more favorable shear vectors for discrete convection, so that's where I'd expect the best tornadic potential to lie the next 2-4 hours or so. The cold core side of this did produce some brief funnels along I-80 back closer to DVN but I have not seen any bonafide tornado reports there. Mid-level clouds, less moisture and perhaps even dust from the southwest hampered the setup there more so than not.

 

[Matthew Crowther]

As I suspected all along, the 10% hatched risk was overdone. Mostly gustnadoes and QLCS spin-ups. Glad I did not chase.