Real-Time Low-Level Wind and Temperature Analysis Using Single WSR-88D Data

Abstract

A four-dimensional variational Doppler radar analysis system (VDRAS) has been developed and implemented at a weather forecast office to produce real-time boundary layer wind and temperature analyses using WSR-88D radar data. This paper describes significant changes made to convert VDRAS from a research tool to a real-time analysis system and presents results of low-level wind and temperature analysis using operational radar data. In order to produce continuous analyses with time, VDRAS was implemented with a cycling procedure, in which the analysis from the previous cycle is used as a first guess and background for the next cycle. Other enhancements in this real-time system include direct assimilation of data on constant elevation angle levels, 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-time analysis system and its sensitivity to various system changes. The quality of the analysis for this case is examined by comparing the subsequent 90-min forecast with the observed radial velocity. It is shown that the forecast initialized using the VDRAS analysis outperforms persistence and a forecast using a mesoscale analysis. The accuracy of the retrieved wind in six convective cases is also verified against automated weather reports from commercial aircraft data. The verification shows an average difference of 3.3 m s?1 over these six cases.