Why model hailstone trajectories, not just thunderstorm counts?

Answer: Stones change along paths

Storm names predict size — No. A storm label is much too coarse to predict hail size. Two storms with similar names or categories can have different updrafts, water content and melting paths. The useful quantity is what the stone experiences while it is carried, grows and falls.

Radar sees every stone — Not quite. Radar is powerful, but it does not perfectly see every hailstone and its whole growth history. Forecasting still needs physical models of air currents, temperature, water and particle paths. That is why NSSL describes models of entire hailstorms, not just radar labels.

Stones change along paths ✓ — Correct. Hail size is shaped by a moving path through updrafts, cold growth zones and warmer falling air. The Nature study used hailstone trajectory simulations, and NSSL also computes projected hailstone trajectories. Counting thunderstorms alone misses whether stones grow, melt or get carried out of the best growth zone.