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Measurement of Snowfall by Radar

Paul E. CarlsonDept. of Meteorology, McGill University, Montreal, Quebec, Canada

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J. S. MarshallDept. of Meteorology, McGill University, Montreal, Quebec, Canada

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Abstract

Using a CPS-9 radar (wavelength 3.2 cm, beamwidth 1°) in dry snow, radar returns from a layer at an average height of 5000 ft were converted to snowfall rates (taking ZR2.0) and summed over 36 hr to obtain a map of snowfall amount. This has been compared with a “climat” map based on depth measurements of new fallen snow at 140 climatological stations within 100 mi of the radar, said amounts ranging from under 2 to over 10 inches. For the 5550 mi2 area within 42 mi of the radar, the average amount by radar was set equal to the average climat amount. The radar/climat ratio was mapped, with the distribution being log normal. For ranges <42 mi, 68% of the data fell between values of 0.76 and 1.32. For ranges between 42 and 100 mi, 68% fell between 0.63 and 1.60. This scatter is about the same as other workers have found for rain. In the relation Z = aRb, a value for b of 2.0 proved appropriate to this particular storm, with some evidence that a slightly higher value might have been a little better.

Abstract

Using a CPS-9 radar (wavelength 3.2 cm, beamwidth 1°) in dry snow, radar returns from a layer at an average height of 5000 ft were converted to snowfall rates (taking ZR2.0) and summed over 36 hr to obtain a map of snowfall amount. This has been compared with a “climat” map based on depth measurements of new fallen snow at 140 climatological stations within 100 mi of the radar, said amounts ranging from under 2 to over 10 inches. For the 5550 mi2 area within 42 mi of the radar, the average amount by radar was set equal to the average climat amount. The radar/climat ratio was mapped, with the distribution being log normal. For ranges <42 mi, 68% of the data fell between values of 0.76 and 1.32. For ranges between 42 and 100 mi, 68% fell between 0.63 and 1.60. This scatter is about the same as other workers have found for rain. In the relation Z = aRb, a value for b of 2.0 proved appropriate to this particular storm, with some evidence that a slightly higher value might have been a little better.

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