Wisconsin Weather > Menomonee Falls Weather. Menomonee Falls, WI climate is mild during summer when temperatures tend to be in the 60's and extremely cold during winter when temperatures tend to be in the 10's. The warmest month of the year is July with an average maximum temperature of 80.20 degrees Fahrenheit, while the coldest month of the year is January with an average minimum temperature of 8.10 degrees Fahrenheit.