Such

dlaczego?
Such a good time,
Such good weather

Gdy oba rzeczowniki sa niepoliczalne?

time w tym przypadku jest policzalne

Nie rozumiem

Z Macmillandictionary.com:
[COUNTABLE] an experience
a good/bad time: It's my job to make sure the guests have a good time.

http://www.englishclub.com/ref/Nouns_that_Are_Countable_and_Uncountable/index.htm