If the height from the lowest level in the RUC native coordinate matches the RUC model terrain height exactly, how can the winds from the lowest native level be non-zero?
The lowest native level is 5m above the surface, strictly speaking, except for its calculations of heights. In other words, the winds, virtual potential temperature, and water vapor mixing ratio can all be considered as 5m above the surface in regard to the atmospheric/land-water boundary. Note Fig. 6 in the Feb 2004 Monthly Weather Review paper about the RUC model on p.482, which shows 2.5m as the half-point between the actual surface and the 5m first atmospheric level. Note also that there are 2-m and 10-m winds in the native file, reduced in a post-processing via Monin-Obukhov similarity.
