In English, if we were to bemoan a situation, say losing your job and getting into a car accident on the way home, we would likely say, “When it rains, it pours.” This implies that when one bad circumstance happens, others are likely to follow. It’s never just one bad thing that takes place. Mongolians have a similar-ish saying: when the rain comes, so do the wolves.

Чоно борооноор, literally “wolf in the rain”, is a phrase rooted in the traditional Mongolian lifestyle: nomadic pastoralism. When storms come, herders round up their flocks or herds for safety, but this is precisely when wolves are prone to attack. They know that the situation is chaotic, the herder has difficulty seeing in the rain, the flocks or herds are skittish and wary because of the storm. With so much going on, the herder has a difficult time keeping track of all of the surroundings, making it much easier for wolves to hunt their prey without interference. Therefore, the saying means that when there are bad/chaotic circumstances, that is when someone is more likely to exploit the situation, usually to take advantage of you.
Example:
You lose your job and are struggling to find a new one. That’s when someone in a pyramid scheme is most likely to try to hire you to become a consultant because the wolves come when it rains.