The patterns associated with light, moderate and heavy snowfall events at Flagstaff, Arizona

Using historical snowfall data from Pulliam Airport in Flagstaff, Arizona snowfall events from November to April between 1975-94 were categorized as light (greater than a trace), moderate (3 to 6 inches) or heavy (greater than 6 inches). The 500 mb height charts associated with light, moderate and heavy snowfall events at Flagstaff were then analyzed. The 500 mb charts were subjectively categorized into pattern types and various parameters for the matching 250, 500 and 700 mb levels were generated and examined. The general conclusion is that broad and/or deeper, slow moving, longer wavelength trough patterns are responsible for the bulk of the heavy snowfall amounts with short wavelength more transient troughs associated with lighter snowfall accumulation. One surprise is that heavy snow amounts can strike Flagstaff in a west to northwest flow regime somewhat against the predominant upslope direction which is south to southwest. Strong jet/front dynamics appear to do much of the work. Also, the upper low can take essentially an inland track over the great basin and still produce heavy snow accumulations at Flagstaff if the wavelength of the trough is broad and slow moving. Light accumulating snow can take place with almost any weak late fall, winter or early spring system at Flagstaff if enough moisture for condensation is present (likely due to wet-bulbing).