This word is typically used with regards to predicting the weather. I use it a little differently.
In relationships, forecasting is when you think about (and worse, TALK ABOUT) how the relationship will end up on your first or second date (or in extreme cases, even before you go out)! Could I marry this person? Could I have children with this person? Etc. You look into the future and predict all sorts of things (and I’ve found that most of the time, the forecast is negative).
Remember, forecasting is not a science and there is a large margin of error. When you forecast you scare yourself, you scare the person you are dating and you might lose out on a great relationship.
Go out on a few dates and live in the moment you are in. Fall into like. Like comes first, love comes later.