If you haven’t looked at the DaySequenceModifierVolume yet, I would suggest having a look at that. It supports DaySequenceCollections or an individual UserDaySequence. It also supports both volume or global effects as well as a UserBlendWeight that you can use to manually drive the transitions between your sequences. This is for example how they made Crime City in Fortnite look like a rainy night whenever players would enter that POI.
So you could still have the DaySequenceCollection representing the weather profile look and then store the probabilities and durations of those volumes in a weather manager that controls the weights of those volumes.