An excessive heat watch will cover many Iowa counties starting Wednesday in anticipation of dangerous heat index values. The National Weather Service says the watch will run through Saturday afternoon as heat index values are expected to soar above 100 degrees. Wednesday's forecast says heat indices along and south of Hwy. 20 will be anywhere from 98 to 106 degrees. That's just a hint of things to come on Thursday as it's forecast to feel like 106 in Ames, Atlantic, and Carroll, and 109 in Ottumwa and Des Moines.