| For the High Plains of Colorado, detailed studies of the evolution of winter storms are foremost in light of the hazards that winter brings to those living and flying in this region. However, relatively little is known of the microphysical and dynamical structure of these storms. Specific issues of importance include the nucleation and growth of ice crystals, production and depletion of supercooled liquid water, processes involving precipitation formation, and dynamic effects including topographic forcing, cold-air damming, and barrier jets.; This thesis addresses these issues by investigating a deep cyclonic winter storm and heavy snowband which passed through the Winter Icing and Storms Project (WISP) network in March 1991. To complement the observational study of this system, the microphysical and dynamical features of the storm were simulated using the three-dimensional Nonhydrostatic Modeling System (NMS). The NMS incorporated an enhanced microphysics package, which included multiple ice-crystal habits (MH) with double moments, terminal velocities based on particle Best number, numerically computed collision efficiencies, and ventilation coefficients based on three-dimensional numerical studies.; The model provided details of the winter storm which were not available from observations. Some important results included: (1) dendrites were the most predominant crystal type followed by columns, (2) dendrites were nucleating near 4 km, corresponding closely with maximum condensate delivery early in the snowband life, (3) rapid diffusional growth of intricate dendritic crystals depleted cloud water efficiently, leading to rapid aggregation and increased precipitation early in the snowband, (4) reduction of 700-mb moisture behind the cyclone, and continued moisture advection below, greatly reduced precipitation as less moisture was supplied to dendrites but more to needle, sheath, and broad-branched crystals, (5) aggregate and ice hydrometeor structures in the storm were highly dependent on the simulated ice-crystal habit, (6) the MH simulation produced precipitation rates and hydrometeor fields which matched observations more closely than did the single-habit simulations, (7) snowband forcing was through convergence along the cold front and static instability above 700 mb, and (8) barrier jet development was induced by flow over higher topography, which then induced snowband initialization. |
