Precipitation Processes within Wintertime Clouds Over Central Saudi Arabia

On January 7, 2007 a narrow band of strato-cumulus clouds formed north of Riyadh and produced weak radar echoes and rain showers. These continental clouds (cloud base temperature +5 C) were able to produce drizzle drops and rain drops via a coalescence process by the time cloud tops reached the -10 C level, within a relatively shallow convective cloud layer approximately 1800m thick. The WMI Lear Jet collected microphysical in-situ data from first-echoes of approximately 10 dBZ, and an instrumented Cheyenne II collected aerosol data within and below these clouds. Precipitation formed via a graupel process originating from large frozen drops. A conceptual model of wintertime clouds over central Saudi Arabia has been developed.