The above Tornado Watch was recently issued for portions of Illinois and Missouri (as well as extreme eastern Iowa) until 1am CDT Monday morning.
Thunderstorms are beginning to fire further Southward along the cold front along the Iowa/Illinois border, and into northeast and northcentral Missouri. This activity will move and develop East/Northeast across the region during the evening hours.
Large hail, damaging winds and isolated tornadoes can be expected with storms that become severe.
Satellite and radar imagery indicate additional cumulus towers building Southwestward along the front, to the South of this watch over southwest Missouri and portions of eastern Oklahoma, and as far south as northcentral thru westcentral Texas (see visible satellite image below):
A strong capping inversion is in place across this region, which has inhibited vigorous thunderstorm development so far. If a thunderstorm manages to develop and organize prior to sunset, it would likely become severe, with large hail, damaging winds and an isolated tornado possible.
A greater threat for more widespread development appears likely in this region after sunset, as the cap weakens. A solid to broken line of thunderstorms is likely to form along the front / dryline later this evening into tonight, however widespread severe weather prospects would slowly diminish with the loss of daytime heating.