This presentation describes orographic processes that modulate the Great Plains low-level jet (LLJ) and related hydrology of the Mississippi River Basin. We emphasize mechanical flow deflection produced by the Rocky Mountains. Although the mountain profiles are fixed over periods of short to medium range climate changes, their influence on the LLJ is not stationary because evolving ambient flows produce changing LLJ responses. Seasonal and longer term changes of the ambient flow occur on large scales, while the response of the LLJ occurs on smaller scales associated with cloud generation and precipitation fields. Orography thus provides a scale transfer mechanism that focusses global-scale features into the regional scale responses. These are relevant to precipitation distribution and to moisture budgets of the larger individual river basins comprising the GCIP domain. We summarize the evidence for the scale transfer in the climatological seasonal cycle of the LLJ and ambient flow, as well as in anomalies from the regular seasonal cycle.