NCEP's Twentieth Century Reanalysis (V2) provides daily variables from 1871/01/01 to 2012/12/31. Monolayer analysis variables are made available in a regular grid and forecast variables in a gaussian grid. This distinction is made very clear in their list on their webpage, although I think the grid is not the main problem here, but the terms in bold.
Daily precipitation rate, for example, is a forecast variable. This makes you think weather you may use forecast and analysis interchangeably. What are the main differences? Any pros or cons? Are all of these still considered reanalysis? Any assumputions I need to make?
This question came up as a consequence of the discussion held here.
Thank you in advance.