Flooding and Hail in Illinois, September 22, 2000

Early in the afternoon, surface low pressure was located between Omaha, Nebraska and Ames, Iowa with a strong cold front draped south from the low pressure through Central Kansas. A strong warm layer of air aloft, or cap, prevented convective development until very late in the afternoon when the cap eroded with diurnal heating and low level moisture advection. A line of strong to severe thunderstorms erupted along the cold front from Northwest Missouri into Eastern Kansas. Other scattered strong to severe thunderstorms developed in Southern Iowa along a warm front, and propagated eastward into West Central Illinois during the evening. The initial storms along the warm front were marginally severe, due to the lack of solar insolation and very moist conditions which limited the formation of strong updrafts. There were several reports of pea sized hail and winds to 50 mph, with isolated reports of dime sized hail and damaging winds. The line of convection which formed out in Missouri and Kansas swept across Southeast Iowa and West Central Illinois during the mid evening. This convection was stronger and aided by lift from the approaching cold front. These storms produced very heavy rain and a few reports of large hail and damaging winds.