Final answer:
A cold front is indicated by a wind shift from south/southwest to north/northwest, and by the presence of tall and dark cumulonimbus clouds associated with thunderstorms.
Step-by-step explanation:
A cold front is a boundary between a cold air mass and a warm air mass. When a cold front approaches, the wind pattern changes. Before the front arrives, the wind usually blows from the south or southwest. As the front passes, the wind direction shifts to the north or northwest. This change in wind direction is known as a wind shift.
Clouds also provide clues about a cold front approaching. A cold front often brings clouds that are tall, dark, and billowy, called cumulonimbus clouds. These clouds are associated with thunderstorms. So, if you see tall, dark clouds and hear thunder, it could indicate that a cold front is approaching.