Cherubi Evolution Pokémon GO is a weird case. Cherubi evolves into Cherrim, who can have two forms. How you get these forms in Pokémon GO isn't intuitive at all, so here's everything you need to know about evolving Cherubi.
Cherubi Evolution Pokémon GO Explained
In the main series games, Cherrim changes forms from Overcast to Sunshine when the weather becomes sunny. Pokémon can't have dynamic form changes in Pokémon GO, so this evolution works differently.
The form of Cherrim you get on evolution is totally random, no matter what the season is or how the weather conditions are. It doesn't make a lot of sense given the lore of the Pokémon, and that Eevee has a lot of care taken for its evolutions.
Luckily, Cherrim itself is quite common and can be caught in either of its forms, depending on the weather. It's only here that the weather conditions have any sway over Cherrim's forms.
Cherrim isn't a powerhouse Pokémon by any means, but the weird evolution pattern may be worth keeping for you collection.