Why not measure the weather once a week? Seven days a week, why seven days? Does this have anything to do with three days cold and four days warm?

You mean the weather forecast. It is also a weekly forecast like people go to work. Very creative. Let's start with seven days, because the weather forecast is limited to the technical level, so it's not three days or fifteen days. Of course, three days is more accurate, but it cannot meet the needs of society. You can force it if necessary, but you are not sure. At the same time, the weather conditions are constantly changing, so these seven days are rolling. For example, 1 reported the weather from 2nd to 8th in the afternoon, and reported the weather from 3rd to 9th in the afternoon on 2nd, including the weather on 3rd, but the forecast on 2nd was much more reliable.

In addition, according to your meaning, if Monday is counted as a week, then it can be reported on Sunday from next Monday to Sunday, then Wednesday can only be reported on Thursday to Sunday, and Saturday can only be reported on Sunday. The final time limit is only 24 hours, which obviously cannot meet the needs of society.

It has nothing to do with how cold and warm you say.

I hope I can help you.