WHAT...Flooding caused by excessive rainfall is possible. 
WHERE...Portions of Iowa, including the following counties, Harrison, Mills, Monona, Montgomery, Pottawattamie and Shelby and Nebraska, including the following counties, Antelope, Boone, Burt, Butler, Cass, Colfax, Cuming, Dodge, Douglas, Lancaster, Madison, Pierce, Platte, Sarpy, Saunders, Seward, Stanton, Thurston, Washington and Wayne. 
WHEN...From this afternoon through Sunday afternoon. 
IMPACTS...Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Flooding may occur in poor drainage and urban areas. 
ADDITIONAL DETAILS... - Recent thunderstorm activity has caused soils to become saturated. Additional rainfall, which could be heavy at times, may lead to flooding in urban and low lying areas. - http://www.weather.gov/safety/flood

You should monitor later forecasts and be alert for possible Flood Warnings. Those living in areas prone to flooding should be prepared to take action should flooding develop.