Final answer:
The maritime tropical air mass affecting Chicago's weather usually comes from the Gulf of Mexico, bringing warmth and humidity.
Step-by-step explanation:
The maritime tropical air mass that influences weather in Chicago, IL typically originates from the Gulf of Mexico. These air masses are characterized by warm temperatures and high humidity, which can contribute to the city's weather patterns throughout the year.
The Gulf of Mexico, being quite warm, serves as a source of moisture and accumulated heat, which is then carried by atmospheric currents towards the northern regions, including Chicago, affecting its typical weather pattern.