What could have been different on Day 2 to cause rainfall?

Responses

a
The air parcel was cooler than the surrounding air on Day 2, so it gained energy on Day 2 but not on Day 1.
The air parcel was cooler than the surrounding air on Day 2, so it gained energy on Day 2 but not on Day 1.

b
The air parcel was warmer than the surrounding air on Day 2, so it gained energy on Day 2 but not on Day 1.
The air parcel was warmer than the surrounding air on Day 2, so it gained energy on Day 2 but not on Day 1.

c
The air parcel was warmer than the surrounding air on Day 2, so it lost energy on Day 2 but not on Day 1.
The air parcel was warmer than the surrounding air on Day 2, so it lost energy on Day 2 but not on Day 1.

d
The air parcel was at the same low temperature as the surrounding air on Day 2, so it had low energy on Day 2 but not on Day 1.

The air parcel was at the same low temperature as the surrounding air on Day 2, so it had low energy on Day 2 but not on Day 1.