Final answer:
A mesoscale convective complex is most likely to develop in the Great Plains region of the United States, which experiences frequent severe weather events during the spring and summer months.
Step-by-step explanation:
A mesoscale convective complex is most likely to develop in the Great Plains of the United States. The Great Plains region, which includes states like Kansas, Nebraska, and Oklahoma, is known for its frequent development of severe thunderstorms and mesoscale convective complexes. These weather systems typically occur during the spring and summer months and can produce heavy rainfall, strong winds, hail, and tornadoes.