Storm motion (ground truth)

Storm speed: 1.20 cells/frame Storm direction: 40°

Optical flow (Lucas-Kanade)

Estimation window: 6 cells Nowcast horizon: 10 frames

Playback

Playback rate: 1.0×

Flow & forecast stats

Frame t0.0

Estimated flow—

True bulk flow—

Nowcast RMSE—

Persistence RMSE—

Skill vs persistence—

Every frame, a real Lucas-Kanade optical-flow solve builds the 2×2 normal-equation system Σ[Ix²,IxIy;IxIy,Iy²]·[u,v] = −Σ[IxIt,IyIt] from actual image gradients between the previous and current precipitation frame, per window block. The resulting vector field is then used to semi-Lagrangian-advect the current frame forward by the chosen horizon — no hand-scripted motion, the arrows and the nowcast are both driven by the measured flow.