Tornado watch issued for Alton, Edwardsville with a few tornadoes likely

A tornado watch was issued Sunday for parts of central and southern Illinois, southwest Indiana and southeast Missouri, including Alton and Edwardsville, as storms were expected to strengthen through the afternoon and evening.

The National Weather Service Storm Prediction Center said the watch was in effect from 1:30 p.m. to 9 p.m. CDT on June 21. The forecast called for thunderstorms to intensify across the watch area, with the potential for damaging winds up to 70 mph, large hail up to 1.5 inches in diameter and possible tornadoes.

The watch carried an elevated tornado risk. The Storm Prediction Center listed a 60% chance of two or more tornadoes and a 40% chance of at least one EF2-or-stronger tornado.

What the watch covered

The watch area stretched beyond the Alton-Edwardsville corridor and included a broader multistate region. The National Weather Service said conditions were favorable for severe thunderstorms and tornadoes in and near the watch area.

The St. Louis weather office urged people to know where to go if a tornado warning was issued and to be ready to move quickly if warnings developed.

How the situation developed

The Intelligencer published its initial report on the watch at 2:23 p.m. CDT, shortly after the alert began. Later same-day coverage showed the severe-weather threat escalated in the region, with tornado warnings issued for nearby Illinois counties near Highland, Greenville, Madison, St. Clair and Clinton counties.

That later warning activity indicated the storm system remained active after the watch was issued, even as the original watch window was scheduled to expire at 9 p.m. CDT.

What residents were being told to do

A tornado watch means conditions are favorable for tornadoes and severe thunderstorms, but it does not mean a tornado has been spotted. Residents in the watch area were being told to monitor warnings closely and be ready to take shelter quickly if conditions worsened.

For people in Alton, Edwardsville and surrounding communities, the immediate concern was the possibility that storms could organize into supercells capable of producing damaging wind, large hail and tornadoes before the watch expired.