Storm splits — left and right movers
At a glance
When a thunderstorm splits in two, one half goes right of the mean wind and the other goes left. In most UK setups, the right-mover is the one to watch.
Deep dive
Storm splitting happens when a single cell's updraft bifurcates under strong deep-layer shear. Each half acquires opposite-sign rotation: the right-mover spins cyclonically (anticyclonic in southern hemisphere), the left-mover anticyclonically.
In a curved hodograph (common in NH supercell environments), the right-mover is dynamically favoured — it's aligned with the vertical shear vector and gains rotation from streamwise vorticity. Left-movers in straight-line hodographs can still produce significant hail but are typically shorter-lived.
When a chase target splits, anticipate the right-mover drifting 20–30° right of the mean flow and re-position accordingly.