My local station provides the weather forecast for the week including the high and low temperature for each day. But I’ve noticed that the temperature extremes rarely correspond from one day to the next.
For example, in my city, the high tomorrow is expected to be 30 degrees while the low is 25. However, for the day after, the high is forecast at 18 and the low is at 0. It would seem to me that at 12:00 pm tomorrow, that the temperature should be between 25 and 30, and at 12:01 am, it would almost certainly have to be in that range also, yet it isn’t supposed to be any warmer than 18 degrees at any point during the day.
Do the high and low temperature predictions refer to the daytime only or am I just dumb?
At least in the US, the high is the max temperature during the calendar day from midnight to midnight. The low is the min temp from sunset of the calendar day to sunrise of the next calendar day.
So if today is the Tuesday, the high is what we expect to see during daytime on Tuesday. The advertised low is really the coldest it will get after sunset on Tuesday before it begins warming up after sunrise on Wednesday.
In the UK, they usually say “daytime max” and “overnight low”. The daytime max is the highest temperature between 9am and 9pm, generally, and the overnight low the lowest from 9pm to 9am the next day.
That still wouldn’t account for the big jump between the low of 25 and the next day’s high of 18 though. I guess they mean the overnight temperature will be about 25 at midnight and still falling, and never get above 18 during daytime the following day.
Of course sometimes, especially in winter, the highest temperature is actually overnight, e.g. if it’s a cold frosty day but then a warm front sweeps through bringing rain in the evening.