Outflow boundary is laid up over the viewing area with cumulus trying to overcome cap. Some of them are actually rooting above the cap in the steeper lapse rates. Others are flat & underneath it with some "cap" clouds that look like lids & flying saucers as the warm, unstable surface air rising up to that cap & tries to push through it.
Also, a weak, old, remnant MCV is in eastern/northeastern Indiana. Cumulus are building there, as well.
Temperatures are 88-93 as of 1:45 p.m. with heat indices ranging from the 90s to as high as 103, like at Covington, Morocco & Fowler. The Purdue Airport heat index is in the upper 90s, while we have reached 101 at the television station.
Peak indices will run in the 90s to as high as 107 in the area today.
Meanwhile, MCS & attendant MCV has been decaying over Wisconsin, but is now showing re-development & intensification, prompting Severe T'Storm Watch for a good chunk of Illinois.
Despite lack of good shear downstream, it is highly unstable over a large area. As said, there is also considerable capping downstream, though.
Thinking is that the MCS will continue to develop & form a bit of a cold pool with a relatively slow moving bow or slightly-bowing cluster/mass of torrential storms as it advances southward & southeastward.
It will likely ride instability gradient & outflow boundary south & southeastward with new storms popping on that outflow boundary in our area ahead of it, which will then merge with the bow/cluster/mass.
Around our area & in the watch zone, there is the risk of a couple/few wet downbursts with torrential rainfall & some hail.
These storms will be a bit pulsey with downbursts, heavy rain & hail coming out, then that particular storm should collapse, while others nearby pulse back up.
This model gives you some idea of what to expect with the main details.
That storm cluster's MCV may wind up over southeastern Illinois by Monday midday. An outflow boundary from it may surge back east & northeastward into our area at peak heating.
However, model trends suggests very strong capping & expansion of hot, upper ridge core into our area, effectively putting the kabosh on any storm development.
I would prefer to keep 20% potential in the forecast, however, especially given the uncertainly of how strong the capping & ridging will get.
Tuesday looks extremely capped, but kept 20% potential to account for an isolated storm or two to possibly pop through.
Monday & Tuesday look especially hot with highs 91-95 with heat indices near 100-111.
Very high heat indices & oppressive dew points of 75-78 will be with us Wednesday-Friday with highs 88-94.
50% coverage of storms will do for each of those days. Isolated severe weather & locally-heavy rainfall are likely.
July 4th looks like there will be storms around late afternoon-evening.
Storm risk may continue right through next weekend with the continuation of the heat & humidity. There may be a brief lull July 9-10, before multiple rounds of storms impact the area July 11-12 with one bringing better risk of more widespread severe weather.
Mid-July shows a tendency for cooler, less humid weather, though it will go up at times with some shower/storm action.
Intense heat & humidity should return in late July with strong cap & ridge tending to shut storms off.