Doppler radars are useful facilities for weather data gathering. In this paper, we propose a visualization pipeline to extract and display horizontal wind fields for Doppler radar data. At first, the input radar data are filtered with adaptive filters to reduce noise and enhance features. Then the horizontal wind field is computed by using a hierarchical optical flow method. In the visualization stage, a multi-level streamline construction method is employed to generate evenly-spaced streamlines to reveal the wind field structures.