What does "overnight lows" mean?

Native speaker’s answer
Rebecca
Usually, there is a range of temperatures during the day and at night. There is a high and a low temperature. "Overnight lows" refers to the low temperatures which happen overnight - at night time. Ex: Do you need an extra blanket? I think the low tonight is going to be five degrees Celsius. Ex: The temperature this weekend is perfect for camping! It'll be about 15 to 20 degrees celsius overnight.