What is the actual valid time for RUC fields (e.g., 3h forecast valid at 03z)?
Well, the forecasts in this case are indeed “valid” at 03z, but since many of the observations assimilated in the RUC (and other NWP models) are centered 10-30 min before the hour, the actual valid time is also offset by 10-30 min. This is discussed in Benjamin et al., 2004, Mon.Wea.Rev. See p. 15 in pdf version and p.503 in MWR version.
