The relationship of weather types to dust storm generation in Arizona (1965–1980)

A general classification of dust weather types for Arizona first‐order stations was developed using synoptic data derived from surface, 850 mb, and 500 mb pressure and wind characteristics from daily weather maps for 321 observed dust storms during 1965–1980. Four major dust weather types were identified: (1) frontal, (2) thunderstorm/convective, (3) tropical disturbance and (4) upper level/cut‐off low. Frontal dust storms (Type 1) occur most frequently during the late autumn, winter and spring and can be divided into two subtypes; pre‐frontal dust and post‐frontal dust. Dust storms generated by thunderstorm or strong convective activity (Type 2) are most frequent during the summer months and are typified by large scale pressure pattern variability, particularly at the upper levels of the troposphere. Dust storms associated with tropical disturbances (Type 3) are infrequent at all stations but are typically very intense, long lasting events. The upper level/cut‐off low type (Type 4) dust storms usually occur during May and June and from September to November and are associated with upper level split flow, where high amplitude ridging to the north and troughing to the south occurs across the western U.S.A. Although dust storms can be traced to specific synoptic events, the interannual variability of dust storms shows a strong correspondence to antecedent winter moisture variability, probably reflecting an overriding control by surface crusting and vegetative effects on dust generation.