are high and low temperature forecast from midnight to midnight or sunrise to sunrise?

Answer 1

midnight to midnight

Answer 2

Depends on what type of forecast you are doing. Sometimes in contests they like you to forecast from midnight to midnight (but usually in Z time so everyone is the same).
Usually for operational forecasts, they give you the highest temperature during the day and the lowest temperature during the night. If the high will be reached in the morning, the forecast will indicate that the temp will be falling during the day, since most people expect the high to occur in the afternoon. If the following night will be warmer than the daytime, you can have a low that is warmer than your high.

In short, it depends on what your forecast is for.

Answer 3

When looking at high and low temperature forcasts you need to know what it means. Let's look at an example that if we are looking at the weather right now for high and lows and the forcast says 62/38 that means that your high is 62 and your low is 38. That means that todays high is 62. It also means that tonights low is going to be 38. It doesn't base itself from midnight to midnight or sunrise to sunrise. It's based on the high for the day followed by the low for the next night. Forcasts are changed throughout the day to represent the time of day so this is an easier way to look at the problem.