Investigation of Dendritic Growth/Aggregation Signatures in WSR-88D Dual-Polarization Radar

Forecasting snow totals in real time is a constant challenge for operational meteorologists. One way that forecasters are able to predict snow totals is by using the snow-to-liquid ratio (SLR) which compares the amount of liquid water to the total snow fall. Typically, the 10:1 ratio is applied: if 10 inches of snow was melted down, the result would be one inch of water. However, studies have shown that this 10:1 “rule” can differ depending on geographical region, among other reasons. The SLR climatology published by Baxter et al. in 2005 has been one improvement in forecasting snow totals for different geographical regions. The goal of this study was to use dual-polarization radar data to locate potential dendritic growth zones (DGZ) and aggregation signals that would affect the SLR, and compare any signatures to observed SLRs. Dual-pol radar data was downloaded from NOAA NCEI for several geographical locations including the Midwest, Northeast, and Southeast and was analyzed using the Gibson Ridge Software program, GR2Analyst. DGZs were noted by a decrease in correlation coefficient and increase in differential reflectivity. Surface observations from the Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS) were then recorded and SLRs were calculated from the observations. The results show that there is little evidence for SLR differences between geographical regions based solely on radar data. Snow amounts were higher when the DGZ was present, but there was no statistical difference between the SLRs with and without the observed DGZ or between geographical regions. These results show that using dual-pol radar data may not be the most effective way for determining SLRs from an operational perspective.