Late spring through early autumn (May–October) is the most pleasant time to visit Dubuque. The Mississippi River landscape is at its best in June and July when the bluffs and river islands are fully green. Autumn — particularly late September and October — brings spectacular fall foliage along the river bluffs and the Great River Road, which is the best single reason to time a visit if you have flexibility.
Summer (June–August) is warm and humid by Iowa standards (high 80s°F/30°C) but manageable. Winters are cold and snowy, with January temperatures regularly below freezing. The indoor attractions at the National Mississippi River Museum remain open year-round, but the outdoor experience is limited.
The Galena Country Eagle Watch in January brings bald eagle watchers to the river bluffs on the Illinois side, and Dubuque is a natural base for it.