[ElPeque]

Every hour these models forecast every hour 10 or 15 days ahead. The further ahead they become less accurate of course.

Having all historical weather forecasts is useful to backtest how accurate the model is because you can compare what was being forecasted at the time with what actually happened.

It is also useful to backtest derived models. If you want to figure out how accurate your model is forecasting something like solar power generation while using one of these weather datasets as features for cloud cover and solar radiation, you will want to run the model with the forecast that was current at that point in time. Otherwise you would be "cheating" by using data you wouldn't have had if you ran the model at that time.

In other words, you'd want to "see" the weather as it was being predicted at the time in order to find out what your model would predict for solar power generation.

I hope that makes sense.