Approximately 3 years of visibility data from a 13-station teleradiometer network in the southwest desert is the basis for the analysis presented. Principal component analysis is employed to identify regions of similarly varying visibility for the entire data set and by seasons. 'North', 'Center', and 'South' regions are identified in each of the four seasons. These regions change their size, shape and location somewhat through the seasons and thus are referred to as groups with each group containing four seasonal regions. A method to calculate transport extinction budgets is demonstrated for the three visibility groups.