Estimating the wind bias in solid precipitation measurements using the Geonor accumulating precipitation gauge on the Canadian Prairies

The systematic under-estimation of solid precipitation due to wind is the most significant error in the measurement of winter precipitation. Previous studies have shown that under-estimation of solid precipitation due to wind can be as large as 100%. As meteorological services incorporate Geonor all-weather accumulating precipitation gauges into national networks, it is important to quantify the potentially large systematic errors associated with wind. Due to the large climatic variability across Canada, gauge adjustment procedures will vary with snow conditions (i.e. adjustments for the Canadian Prairies will be different than those for Atlantic Canada). In response to these requirements, an intercomparison program located in the Canadian Prairies has been initiated. The objective of this program is to examine wind induced bias in solid precipitation as measured by the Geonor T-200B gauge in a relatively dry, cold and windy environment. Geonor measurements using a standard Alter-type wind shield and using an octagonal vertical double fence wind shield have been compared to the manually observed Dual Fence Intercomparison Reference (DFIR). Preliminary results suggest that the catch efficiency of the Geonor in the double octagonal fence approaches 100% but catch efficiencies for the Alter-shielded gauge can be as low as 50% at wind speeds of 5 m/s.