Radar observations of snow formation in a warm pre‐frontal snowband |
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| Authors: | Gerhard W Reuter Raymond Beaubien |
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| Institution: | 1. Department of Earth and Atmospheric Sciences , University of Alberta , 1–26 Earth Sciences Bldg., Edmonton, Alberta, Canada , T6G 2E3;2. Environment Canada , Prairie and Northern Region, Edmonton |
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| Abstract: | Abstract Radar reflectivity measurements and sounding data were analyzed to investigate snowfall production in a long‐lasting snowband that formed in advance of a warm surface front moving across Alberta. The sounding data indicated that the band could have been forced by slantwise overturning during the release of moist symmetric instability combined with frontogenesis. The stability analysis presented here is novel in that it includes ice phase thermodynamics, neglected in previous studies of slantwise convection. Radar reflectivity fields were analyzed to determine the total snow content and the mass outflow rate as factors of time. The peak value of total snow content was 17 kilotons per km of snowband, and the peak mass outflow rate was 10 tons s‐1 km‐1. The snowfall rate averaged across the cloud base was about 0.8 cm h‐1, and the average snow content remained close to 0.2 g m‐1. The characteristic time (defined as the ratio of total snow content over mass outflow rate) was about 30 minutes, which is approximately the time needed for the growth of snowflakes by aggregation in the observed temperature range. The precipitation efficiency of the snowband, defined as the ratio of snow mass outflow to water vapour inflow was estimated to be 14%. The precipitation production values observed in the Alberta snowband are compared with previous estimates reported for frontal rainbands and Alberta thunderstorms. |
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