The best explanation for the student's observations is "A cold front moved into the area."
Here's the reasoning:
- On Day 1, the weather is sunny and warm.
- On Day 2, it becomes cloudy and rainy, which is typically associated with a cold front approaching.
- On Day 3, there is a drop in temperature, which is another indicator that a cold front has moved in.
- On Day 4, clear skies and cold temperatures can follow the passage of a cold front, leading to stable and cooler conditions.
This pattern aligns with how cold fronts typically affect weather.