After a break from rains earlier in the week, ingredients are again in place for frequent thunderstorm development. The focus for these storm clusters will be a stationary front lying south of the metro area. This boundary separates early March-level temperatures from mid-summer swelter. While readings held in the mid-40s along the North shore Friday afternoon, temperatures over central Illinois hovered near 90 degrees. Similar conditions will exist Saturday. Very warm, moist air to the south will override a shallow layer of cool air over Chicago, resulting in periodic thunderstorms. Strongest storms are expected Saturday night when flooding rains and large hail are most likely.