"Is it winter now?"
What is the difference between зараз and тепер? That is, would тепер зима be correct?
Зараз - at this moment, immediately
Тепер - nowadays, lately.
Тепер should be used for the longer periods of time and зараз for the things that are true only at some short moment (second, minute, hour)
But lately native speakers started to use зараз where you would usually need тепер and "forgot" about тепер.
As winter is quite a long period of time, тепер would be more appropriate here
I'm not sure if there is any. Both зараз зима and тепер зима seem to be correct.
That's just not how we say it in Ukranian. English needs this impersonal subject (it) to speak about weather, distance, time, Ukrainian doesn't. It's just Зараз зима (It's winter now), Зараз 5 година (It's 5 o'clock now), Сьогодні сонячно (it's sunny today)