Both cities have average annual temperatures of approximately 50 degrees F.
April is a month of great variation in the Midwest - it can snow, with temperatures around freezing, or it can be very warm, in the 80's and even 90's. "Average" weather in April would be high temps around 50 - 70 for both cities.
Winter in the Midwest is generally cold and snowy, but it depends on exactly where you are. In Northern Minnesota, a typical winter day would get up into the 10's F and fall down to the single digits below zero at night; in Chicago, it'd be more like a high of 35 and low of 20. In St. Louis - the southern boundary of the Midwest - snow rarely accumulates for any significant period of time, and winter temperatures are typically in the 40's. Going from west to east, one sees less variation in temperature: in western Nebraska or western South Dakota, "chinooks" can occasion 70-degree days in February, only to have temperatures fall back into bitter cold the next day, but in Chicago or Detroit winter weather is less variable.
How much snow falls in an average year is a function of both latitude and longitude. Obviously, more snow is going to fall the further north you go. Much less known is the effect that longitude has: the general rule is you will see more snow moving from west to east. The same goes with annual precipitation in general.