Well some of that is hyperbole. I mean I think we know when it truly will be Rains to Maines. Get a strong low cutting into NY state, and that's going to happen.
But to your point about calling for AN when there are 2-3 weeks left of a month...there is skill to that. We can look ahead at the model ensembles and have a good idea of what the pattern entails from a temperature standpoint. You look at features that stick out to determine warmer or cold regimes. For instance a ridge across the E/SE US usually means warm weather. A ridge across the west coast into western Canada would likely mean colder weather for us. I look for certain features when I make a call like that. It won't always work out, but usually if one of us mets say a BN or AN month...they see something and they aren't just passively throwing shit against the wall to see if it sticks.