Real-time low-level wind and temperature analysis using single WSR-88D data

A four-dimensional variational Doppler radar analysis system (VDRAS) has be rn developed and implemented at a weather forecast office to produce real-t ime boundary layer wind and temperature analyses using WSR-88D radar data. This paper describes significant changes made to convert VDRAS from a resea rch tool to a real-rime analysis system and presents results of low-level w ind and temperature analysis using operational radar data. In order to prod uce continuous analyses with time. VDRAS was implemented with a cycling pro cedure. in which the analysis from the previous cycle is used as a first gu ess and background for the next cycle. Other enhancements in this real-time system include direct assimilation of data on constant elevation angle lev els. addition of mesonet observations. inclusion of an analysis background term. and continuous updating of lateral boundary conditions. An observed case of a line of storms and strong outflow is used to examine the performance of the real-rime analysis system and its sensitivity to var ious system changes. The quality of the analysis for this case is examined by comparing the subsequent 90-min forecast with the observed radial veloci ty. It is shown that the forecast initialized using the VDRAS analysis outp erforms persistence and a forecast using a mesoscale analysis. The accuracy of the retrieved wind in six convective cases is also verified against aut omated weather reports from commercial aircraft data. The verification show s an average difference of 3.3 m s(-1) over these six cases.