'Temperaturen er den samme i morgen' is marked wrong. Does verb + 'i morgen' not work as a future for 'er'?
Would "Temperaturen bliver den samme i morgen." also be correct? I remember from the future skill that in some of the examples at blive was used like the future tense of at være.
Yes, that would work too.
I would most likely say: "Det bliver samme temperatur i morgen."