A.1 Determine the main idea of a passage R2C
Read the passage.
Creating Lake-Effect Snow
Situated on Lake Erie, the city of Buffalo, New York, is one of the snowiest cities in the
United States. Like other cities on large lakes, it is subject to a phenomenon called lake-
effect snow. Water retains heat, so lake water is often warmer than the air. In the lake
effect, cold air moves over warmer lake water, initiating a process that can produce large
snowstorms. Moisture from the lake evaporates into the cold air, warming it. Because
warm air is less dense than cold air, it begins to rise. As it rises and moves away from the
lake, it cools down. As the air cools, moisture condenses and forms into clouds. If the
temperature is cold enough, the moisture falls to the ground as snow.
What is the main idea of the passage?