Development of a dynamical conceptual model of processes producing heavy banded snowfall utilizing numerical simulations.

摘要

A climatology study listed heavy snowfall as the leading weather hazard in a climatological study. A major subset of heavy snowfall is banded snowfall within an extratropical cyclone. The prediction of these localized snowbands presents a challenge for forecasters.; Investigations of these heavy banded snowfall phenomena have involved observational and numerical approaches. Different processes and atmospheric features have been diagnosed that enhance precipitation amounts within the snowband, including mid-level frontogenesis, equivalent potential vorticity reduction zone, the development of the trough of warm air aloft; (trowal), and the release of conditional symmetric instability (CSI). The aforementioned causes often occur together in the vicinity of an extratropical cyclone.; Sub-synoptic features are often masked in observational investigations due to insufficient spatial and temporal resolutions of the upper-air data. Therefore, smaller atmospheric features can develop, intensify, and dissipate without being recorded by these data. Researchers have used the Rapid Update Cycle-2 model initialization to perform diagnostic studies since it is run every hour. This accounts for the spatial and temporal gaps but still contain the discontinuity of the atmospheric state resulting with each initialization.; Utilizing a numerical model, three events with heavy banded snowfall were simulated. These simulations aided in the investigation of the processes involved in the heavy banded snowfall formation by enhancing the spatial and temporal resolutions and allowing for a continuous model run with a physically consistent framework.; From these simulations, a conceptual model illustrating the development of heavy handed snowfall in the central United States is obtained. This development consists of 4 stages depicting the evolution of the major conveyor belts and their juxtaposition to the critical physical processes. The snowband forms in between the northern extent of the trowal structure and the equatorward side of the mid-level frontogeriesis while located within a region of CSI. The vigorous vertical motions occur 3 to 6 h prior to the maximum snowfall intensity.