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Hello, teachers!

Would you please check if these sentences are acceptable, with nothing, when, that, or where?

1. As of January 8th, 2004, there have been 2 snow days (when/that/where) schools have had to close.

2. The mean number of days (when/that/where) the maximum temperature was equal to or more than 40.0 degrees Celsius is 4.5 [for] each month. [* Can we use or omit 'for' here?]

3. I love and enjoy [the] days (when/that/where) I don't have to wake up, [* Can we use or omit 'the' here?]

Thank you very much.
Best Wishes!
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'Where' is colloquial but a bit strange in (1), Ms. Jandi. I would not omit the relative pronoun.

In (2), all choices are awkward, and it would be better to recast:

For an average of 4.5 days each month, the maximum temperature was equal to or more than 40.0 degrees Celsius.

In (3) the 'the' is optional, and the 'where' again is colloquial but seems strange in print. Because the sentence is simpler, the omission of the relative seems more acceptable to me. It is a matter of clarity in communication, Ms. Jandi.
Comments  
Thank you, MM!
Always great help to me!
Enjoy the deep night of winter.