right. How snowy do we envision Hithlum to be? I think southern Hithlum or Dor lomin and Mithrim should be more hospitable, like the nicer parts of Skandinavia (but still the Easterlings feel betrayed when the land is given to them, so it can't have been too nice either), while the North of Dor Lomin should be more inhospitable. The Region of drengist would lie in between... but i think itself should be rather inhospitable and sad. Hithlum and Mithrim is where men and Elves settle... Nevrast and Lammoth do not seem to have been settled or only have been very thinly populated.
But I think Morgoth#s moods would directly influence the weather in Northern Beleriand... when he#s under siege and weakened the winters might be shorter and more lush while they become longer and more pressing when he#s enraged, growing stronger or going into the offensive...