This study utilized conditional sampling to identify three frequent wind regimes in the lower Sacramento Valley. The major flow features of the mean diurnal wind patterns in the southern Sacramento Valley and surrounding areas were analyzed for each wind regime. Afternoon wind directions at a pivotal observing site (Davis, CA) in the south-central part of the valley were used to classify the regimes as south wind (marine air intrusion), north wind (no marine air intrusion), and transitional wind days. In the summer of 1991, these occurred 72%, 14%, and 14% of the days, respectively. Daily data from 21 surface observing stations were segregated by wind regime, then averaged for quarters of the day to produce wind roses grouped by regime and time of day. These data were then plotted on a base map. The most frequent direction in each of these wind roses was used to construct streamlines for the area by quarter of the day for each regime. These analyses provide a climatology of the diurnal variation ... Abstract This study utilized conditional sampling to identify three frequent wind regimes in the lower Sacramento Valley. The major flow features of the mean diurnal wind patterns in the southern Sacramento Valley and surrounding areas were analyzed for each wind regime. Afternoon wind directions at a pivotal observing site (Davis, CA) in the south-central part of the valley were used to classify the regimes as south wind (marine air intrusion), north wind (no marine air intrusion), and transitional wind days. In the summer of 1991, these occurred 72%, 14%, and 14% of the days, respectively. Daily data from 21 surface observing stations were segregated by wind regime, then averaged for quarters of the day to produce wind roses grouped by regime and time of day. These data were then plotted on a base map. The most frequent direction in each of these wind roses was used to construct streamlines for the area by quarter of the day for each regime. These analyses provide a climatology of the diurnal variation ...