In my review of the Everki Atlas, I pointed that the outside pocket might collect water if it rains. While the rest of the backpack’s contents will be fine, items in that pocket might get wet. Everki does sell a backpack rain cover that can protect the backpack but it is outrageously expensive.
Instead, I got the Ayamaya 40L raincover from Amazon. It is a fraction of the price and easily fits the Atlas. I also like the fact that the Ayamaya doesn’t have any logos on it and is just a cover.