What is meant by the term JAM?
It's not an acronym. The reference is to the cynical old saying "Jam yesterday, jam tomorrow, but never jam today". So "more jam tomorrow" was, I imagine, suggesting that though the model might be forecasting something good in the future, it's done it before without it actually happening, and this is likely to be another such occasion.
My apologies to the OP if I've totally misinterpreted them!"