The temperature fell suddenly.
Today's highest temperature will be 40 degrees.
There is a large temperature gap between morning and night.
The energy of the warmth will cause the temperature to go up and down. Energy goes up? Higher temperature because of more movement and activity. Energy goes down? Well, temperature gets colder and slower.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.