1 °C. In most years, Denver averages a daily maximum temperature for April that's between 56 and 66 degrees Fahrenheit (13 to 19 degrees Celsius). The minimum temperature usually falls between 31 and 37 °F (0 to 3 °C).The days at Denver continue warming during April.early every day in April warms to over 40 °F (4 °C) in Denver. The city averages 8 days this month when the thermometer reaches into the 70s °F (over 21 °C).