Well... you are the programmer, so you decide, but my proposal should be easier to implement.

In any case, my constraints were:
-easy to read
-should not take extra screen space
-should not imply vast changes in the programm code.

BTW, about screen space: I normally only use 3 icons. I don't have much space for more, and 3 days previsions are already very innacurate, so...