Dual-polarized radar observations of precipitation during SNOW-V10

The NOAA/NSSL NOXP mobile dual-polarized X-band radar was deployed in northern Washington (to the south of the Canadian Cascades) as a part of the Science and Nowcasting of Olympic Winter games/Vancouver 2010 (SNOW-V10) effort. The polarimetric variables measured by the radar allowed unique insight into the microphysical properties of the precipitation which is demonstrated using data collected from 24 – 28 February 2010. Three distinctive facets to the precipitation are noted. 1) The “strength,” depth, and base of the melting layer (ML) were non-constant and changed quite rapidly. Sometimes, within a matter of 10 – 30 minutes, the maximum differential reflectivity (Zdr) and minimum cross-correlation coefficient (Rhv) in the ML changed by as much as 3 dB and 0.3, respectively and the depth and base changed by as much as 300 m. The latter is likely due to latent cooling while the former is due to changes in the hydrometeor type and concentration. 2) The ML consistently had a downward tilt toward the north ranging from 200 – 500 m. The magnitude of the tilt appears to be related to the elevation (with lower elevations having a larger tilt) and the characteristics of the ML (with stronger MLs having a larger tilt). A downward tilt to MLs incident to terrain have long been noted, but the above suggests the tilt is strongly modulated by microphysical effects. 3) Numerous waves propagated through the ML during the time period considered. These were associated with lower Rhv and higher Zdr in the downward descending portion of the wave, suggesting local modification to the microphysical properties was taking place as the waves moved through. Overall, the X-band radar shows great potential for the now-casting of precipitation type over regions of elevated terrain.