I don't know if it is grammatically incorrect to omit "are reached", but it would sound better if you added it, I think.
You have to add either a date or an event after "until".
- until tomorrow (date)
- until my sister graduates (event)
If you just wrote "until the maximum temperature", it would be kind of like I only wrote "until my sister". Even though, people can understand what your sentence means from the context...
Edit: I forgot to specify that I'm not a teacher... Perhaps someone will disagree.