I think Northern Illinois looks chasable tomorrow, perhaps from about Rock Falls to Peoria, depending on the warm front. I don't take ETA's diffuse surface features at face value because I think that if the shortwave verifies at ETA's projected intensity, surface features will react more favorably than shown.
This is an amateur observation, but it seems to me that with these late or early season events, ETA parses the mandatory heights a little too much. What I mean is that with a June-style s/w aloft, it still wants the surface to look docile as August. Still it's true that Big Mama Climo likes to stomp into these events and shove the calendar down our throats, so, after a 1500 mile bust we say: "Damn it, I'll never chase in [February, March, July, August, etc] again!" So maybe ETA is right to keep an eye on the season and resist anomolous patterns, which this summer has certainly been so far. The whole year, for that matter.
Still, with helicties around 300 m2/s along the stationary front, 3000 or more j/k CAPE is sufficient to spin an updraft or two and worth a 5% tornado probability.
ETA shows a lot of precip early and flow aloft suggest MCS evolution eventually, no question, but I think a small window of isolated storms could open particularly along the front between 19 and 21Z, if the ETA verifies with s/w passage.
My Illinois curse is approaching Naftel-ian proportions and so I'll stay home and watch the action on the internet. Good luck to all who go!
