I will try to describe my point of view on the differences:

• Geralt: Aard vs. Caretaker: Similar

• Nirthal/Gaunter vs. 1st Crone/2nc Crone: Similar

• Toad/Double-Cross vs. 1 Crone/Speartip: Deck thinning vs. value

-> I find Speartip to be clunky in a weather deck, since the row you want to use speartip on, is often the row you want to weather. Also, the value difference here is not very big, imo.

• Ocvist vs. Scorch: Card advantage vs. potential swing

-> Card advantage is invaluable in my eyes, and Scorch is less necessary in a weather deck, since you weather the high power cards (as long as you have card advantage)

• Drowners/Ekimmara vs. Ancient Foglets: capability to set up for weather vs. similar value, but no extras

-> I see no negatives to get rid of Ancient Foglets here. I would not replace them with Wyverns, since that conflicts with weather (you have already cards conflicting with weather).

• Swallow potion vs. Alzur's Thunder -> Similar

• First Light vs. 2nd Impenetrable Fog -> Deck thinning vs. extra fog consistency

-> With all the deck thinning, the 2nd Impenetrable Fog is not required. Also, there is generally no need for fog in the round you want to lose.