It cooled down at night although it was so warm during the day.
It was chilly in the morning and at night but it warmed up during the day.
cool down: 冷え込む、寒く（涼しく）なる
warm up: 暖まる
during the day: 昼間、日中
It cooled down at night although it was so warm during the day.
（訳1）昼間はとても暖かかったのに夜は冷え込んだ
It was chilly in the morning and at night but it warmed up during the day.
（訳2）朝晩は寒かったが、昼間は暖かくなった
朝と晩を両方入れようとすると少ししつこくなってしまうので、（訳1）のように片方だけにしてもよいでしょう。夜が寒ければ朝もそうであることは想像がつきますよね。
また、（訳2）は逆の発想で、昼間は暖かくなった、としています。こちらなら朝晩双方を入れてもそれほど無理には聞こえないような気がします。
Normally, when the weather changes, we simply say the weather has broken. "I can't wait for the weather to break. I am tired of this heat!" When the weather is cooling, you can also use the term "chilly". "It is very chilly now." Another useful term is "brisk". Brisk refers to being very cold. "It is very brisk out!"
一般的に、天気が変化することは、"the weather has broken"と言います。
"I can't wait for the weather to break. I am tired of this heat!"
（天気が変わるのが待ち遠しいよ。この暑さにはうんざりだよ！）
天気が寒くなってきているときには、"chilly"という表現も使えます。
"It is very chilly now."
（今はとっても寒い）
"brisk"も便利な表現です。"brisk"はとても寒いことを表します。
"It is very brisk out!"
（外はとっても寒い！）
It was cold in the morning and at night, even though it was warm during the day.
The day started out cold, then it warmed up during the day. It got cold again at night.
The morning and night was cold, but it was quite warm during the day.
When you want to explain that the morning and night was cold but it was warm during the day; then you can say it in the following ways:
-It was cold in the morning and at night, even though it was warm during the day.
-The days started out cold, then it warmed up during the day. It got cold again at night.
-The morning and night was cold, but it was quite warm during the day.
朝晩は寒かったけど昼間は暖かかったと伝える言い方です：
【例文】
-It was cold in the morning and at night, even though it was warm during the day.
［訳］昼間は暖かかったけど、朝晩は寒かったです
-The day started out cold, then it warmed up during the day. It got cold again at night.
［訳］朝は寒かったけど、昼間は暖かくなって、夜はまた冷え込みました
-The morning and night was cold, but it was quite warm during the day.
［訳］朝晩は寒かったけど、昼間はかなり暖かかったです
As winter comes, it is generally cooler in the early morning and at night time. We may say the nights are drawing in to indicate that it is darker earlier and for longer and therefore colder. A more fun way of saying this is "jack frost is nipping at our heels". This indicates the cold nights and early mornings when there still might be the biting cold of frost about.
冬が来ると、朝と夜が冷えますね。
"the nights are drawing in"（日が短くなってきた）は、日が短くなって寒くなってきたことを表します。
もっと面白い言い方として、"Jack frost is nipping at our heels"（霜がかかとにしみる）があります。これは、霜が降りるような寒い朝・夜を表します。
During the day it is warm, but it gets colder at night and in the morning
It's only cold during the evenings, at night and in the morning
It's warm during the daylight, but after the sun goes down, it gets cooler
It is very common during the spring or autumn seasons that the sun warms up the day during the sunlight hours, but the air is actually quite cool. So when the sun sets and before the sun rises it can be quite chilly. As we approach winter, in the fall season, the evenings get cooler and cooler, and the mornings can be quite cold, but when the sun comes out, it tends to warm up the air around us, and we can describe the day a warm. The nights can be cold, a long time after the sun goes down, and the morning may be very cold because it is many hours without sunlight to warm up the surroundings. But as the sun comes out, the day can be warm and pleasant.
During the day it was rather warm, throughout the night til morning it was cold.
Even though it was warm in the daytime, the night and morning were chilly.
It was warn in the day, but it was a cold night and morning.
"Even though it was warm in the daytime, the night and morning were chilly." can tell how the weather in the day was warm and how through the night until the morning, it was cold.
"Even thought it was warm in the daytime, the night and morning were chilly."（日中は暖かったけれど、夜と朝は寒かった。）
こちらの例文は、日中は暖かく、夜から朝にかけて寒かったことが分かる文章です。
日本 
アメリカ合衆国 
南アフリカ 
イギリス 
