A warm front is the transition zone which develop in a region where warm air replaces the cold air. The air behind the warm front is warmer than air in the front. When the warm front reaches a region with colder air, the cold air gets warm and more humid. Warm front brings changes in weather condition of a region. The increase in humidity in air results in rainfall and temperature becomes warm.
Therefore, a warm front heading toward Chicago will result in warm and rainy weather.
