2026-03-10 EVENT: IL/IA/MO

[Jesse Risley]

The lake breeze may end up creating a NW-SE oriented warm front that edges south as a cold front (on the eastern flank) owed to the nascent lake breeze boundary. This will limit spatial availability of storms to take advantage of the best low-level SRH given bunkers right storm motions as depicted on soundings. Line parallel shear vectors are also not oriented favorably for long-term discrete supercells as CAMs depict a rapid movement to QLCS. Tornadic potential looks best, at least to me, early on in the event northeast of the surface low across extreme E/SE IA into W/NW IL proximal to the WF after storms initiate. Most models now seem to be gravitating towards the robust CINH holding till around 23z-0z/11 with explosive development thereafter. I wouldn't be surprised if a warm bias in the models is overdoing the WF progression and it really ends up somewhere closer to or just south of I-80 but we'll see (some models this morning have it jumping up or past I-88). It looks like most of the convection east of I-39 in IL may be north of the effective WF but I agree with @Dan Robinson that there is always the potential for an isolated cell or two further east of the main forcing into eastern IL or NW IN. Climatology to me favors that golden triangle north of a KEOK to KDVN to KGBG, or thereabouts, depending on position of the warm front and whether or not a pre-frontal axis of convergence sets storms off just west of or immediately east of the Mississippi River (probably 25-30 miles either side thereof) with favorable juxtaposition of the surface warm front. This morning's CAMs are favoring the IL side of the river for the most robust convective placement.

 

[Bobby Little]

for what its worth

 

[Luke Penney]

Recent HRRR has a number of runs with mid-/early-afternoon storms starting in central Illinois, where the parameter space isn't as good but it's less likely to get uncut by cold air. Later storms in northwest IL often have better parameters but are more likely to have issues with low-lying cold air and starting around sunset.
And then there's a lot of variation between models for when and where storms initiate.
I expect this one will need some careful playing-it-by-ear to decide where to go.

(Edit: And the further north you go, the better the hodographs get and the more vorticity there is due to the front, but the higher the odds get of low-lying cold air due to the front.)

 

[Dan Robinson]

When I went outside this morning, I was struck by the very conspicuous lack of strong southerly winds that you normally want to see when you wake up on a chase day. Models agree this will improve, but a light breeze at 10am isn't exactly great for a storm at 3pm, especially with stronger northerlies upstream on the cold side of the boundary than the southerlies coming up south of it. The HRRR sure does want to throw a lot decoy storms out there. Other CAMS are at least consistent on the storm of the day. Bloomington's got a dewpoint of 63F this morning, that's good - but the depth of that looks a on the shallow side per the 12z ILX sounding. The HRRR was mixing that out like crazy last night, but it's come in line with the other models on that this morning.

 

[Luke Penney]

The HRRR sure does want to throw a lot decoy storms out there. Other CAMS are at least consistent on the storm of the day.

You're thinking late-afternoon storms in northwestern IL is today's game? When you say "decoy," are you thinking that the potential earlier-afternoon storms HRRR forecasts are unlikely to happen, or that if they do they're enough less likely to be tornadic that a chaser would be better off targeting the later storms? (I think this is where my lower level of experience is showing, so I'm wanting to learn more about these kind of details.)

 

[Blake Naftel]

My focus is primarily on the southwest tier of Lower Michigan into Northwest Indiana, mostly due to proximity to home, but also consistent model trends for later this afternoon towards sunset. Most CAMs bring the very pronounced warm front north to the I-94 corridor in LM, and beyond the cool lake breeze boundary that eludes to keeping Chicagoland on the safe side, the timing and parameter space in the warm sector tends to present a lead supercell scenario "somewhere" along or south of the I-80/90 toll road zone followed by more QLCS mode of storms post sunset for most of the region. Granted the NAM3k eludes to this as well only further southwest into north-central Illinois. At present, either side of the I-80/90 toll road would present a substantial tornado risk after 5 p.m. ET. Will be watching!

 

[Patrick K]

12z and later CAMs are pretty consistent on IL/IN supercells initiating prior to sunset and maintaining themselves close to and south of the front. SPC just upgraded to moderate. The good news is that this area of the country is pretty chaseable with good road network. The bad news is that it seems somewhat time/space limited, either with storms being undercut, sunset arriving, or storms moving through prior to the LLJ really ramping up. Wishing everyone best of luck on the weather and that other chasers can keep their heads screwed on straight.

 

[Mike Smith]

FWIW, the 14Z Nadocast forecast often lowers the odds from 12Z for non-meteorological reasons. The probabilities will likely go up on the 18Z version.

 

[Dan Robinson]

Lake breeze is still on the move. Still a stronger push on the north side than the south, favoring continued southward/westward progression. The eastern side of it has slowed, but this area has been - all day so far -socked in with clouds. Cu field for the western area is getting agitated. Decision time needs to be soon between eastern or western side. Leaning on west currently, but if the eastern end of the boundary can start getting pushed back, it will be the better play..

 

[Jesse Risley]

Missou's (KCOU) 18z sounding still shows a cap but that's pretty far south of the WF. Waiting on DVN's 18z launch data right now. ILX doesn't show as much of a cap though low-level shear is still a bit anemic there. CAM's have been pretty consistent in firing deeper convection near the I-74/I-80 terminus this evening with storms propagating eastward along the WF. I've got quite a bit of agitated Cu here in the Macomb area right now.

 

[Patrick K]

FWIW, successive HRRR runs show later and more western initiation, and also show the slight southerly displacement of the front in northern IL noted by Dan. Unfortunately, this appears to increase probability that storms cross the front, but fortunately may also increase probability of riding/interacting with it.