A Climatology of Transition Season Colorado Cyclones: 1961–1990

Abstract

Frequency, track, and intensity characteristics of transition season Colorado cyclones are investigated for the period 1961?90. Monthly cyclone totals are examined for evidence of seasonal frequency variations during the study period. Cyclone track maps for the months of April, May, October, and November are produced and analyzed for variations in azimuth and movement rates. In addition, the monthly distributions of minimum central pressure values are discussed. Transition season Colorado cyclone annual frequencies declined significantly during the period 1961?90, although the decline occurred primarily during the spring months. April has the most Colorado cyclone occurrences of the months examined. Spring and fall Colorado cyclone tracks are shown to be similar in trajectory and 48 h azimuth, though slightly variant in movement rates. Cyclones developing in months closer to the strong Northern Hemisphere winter circulation (April and November) regime tend to be more vigorous in terms of central pressure and closed circulation than those developing during late spring and early fall (May and October).