Thanks for the great question Mohammad. There's actually a lot of uncertainty around jet waviness - eg here's a recent study suggesting it's not increasing as much as was thought: https://doi.org/10.1126/sciadv.aay2880. 

In terms of seasonal predictions, these can capture wavy jets if there is a predictable seasonal forcing, such as the La Niña this year. 

Often the waves are sub-seasonal features though, and are less well captured by the seasonal forecasts. There can be skill in these at shorter lead times, say over a few weeks, especially if there is some other predictable forcing such as the Madden-Julian Oscillation.