1. S-Band Radar Dual-Polarization Observations of Winter Storms P. C. Kennedy and S. A. Rutledge CSU-CHILL Radar Facility

2. CSU-CHILL Data Overview 3 dB beamwidth ~1 o Alternating H, V transmit polarization 11 cm wavelength Scan rates 6-10 o s -1 PPI and 1 o s -1 RHI Wang and Chandrasekar (2009) Kdp Data collected when significant winter precipitation expected within ~100 km of Greeley, CO

3. 20 Dec 2006 1419 UTC 3.5 o PPI data Temperatures from 12 UTC DNR sounding Reflectivity (dBZ) Kdp ( o km -1 x 10)

4. 20 Dec 2006 1442 UTC 3.5 o PPI data Reflectivity (dBZ) Kdp ( o km -1 x 10)

5. 20 Dec 2006 1504 UTC 3.5 o PPI data Reflectivity (dBZ) Kdp ( o km -1 x 10)

6. 20 Dec 2006 1504 UTC 3.5 o PPI data Unfolded radial velocity (ms -1 ); multi-day KDEN closure starts ~22 UTC

7. 20 Dec 2006 1502 UTC 156.8 o RHI Aggregation reflectivity profile; max Kdp layer aloft Reflectivity (dBZ) Kdp ( o km -1 )

8. Storm 2: 18 March 2003 Kdp ( 0 km -1 x 10) at 4.2 o PPI as heavy snow period starts at KFCL Rings are -10, -15, -20 o C from LBF 12 UTC sounding 1844 UTC 2004 UTC

9. Height profiles extracted from RHI scan data in the two storms Kdp max near -15 o C level; polarimetric traces imply aggregation with descent

10. T-Matrix simulations of Kdp generation from ice particles Lo and Passarelli (1982) DSD: 0.2 to 2.0 mm diameter “dendrites” “Aggregated” particle population: Kdp=.09 o km -1 ; Zdr=0.3 dB; Zh=19 dBZ

11. Summary Several 10 th ’s of a o km -1 Kdp values observed at S-Band in major winter storms (see also Trapp et al 2001.) Kdp values maximize near the -15 o C ambient temperature level Scattering model results suggest that suitable populations of dendritic crystals can generate observed Kdp magnitudes (in situ obs needed) Positive Kdp areas near -15 o C level may be an indication of active dendritic particle growth