Colors show the hourly forecast across greater Boston, blended between forecast points about 3 miles apart. Rain streaks get denser where it is heavier and drift with the wind.

Course colors show the wind each stretch faces while racing upstream from the start to the finish. Drag the map to move around, and scroll or pinch to zoom. The course line follows the river's centerline from OpenStreetMap over the 3-mile course. Wind streaks travel at the true ground speed for the current zoom, multiplied by the playback rate in the map corner, and gusts sweep through as faster bands.