Rainbows are a common sight at Niagara Falls. With the right combination of sun and mist, rainbows can be seen on any given day at Niagara Falls. The chances of seeing a rainbow vary depending on the weather conditions, but generally speaking they are quite good. On sunny days, when there is sufficient mist coming off the falls to create a prismatic effect with sunlight, rainbows are almost certain to appear. On cloudy days or rainy days however, it is less likely that you will see them.