Parameters & indices#shear#structure

Bulk shear (0–6 km)

Also: shear · deep-layer shear

At a glance

The vector difference between surface wind and the wind at 6 km — the single best predictor of whether a storm will organise into something dangerous.

Deep dive

Bulk shear is the magnitude of the surface-to-6 km wind vector difference in m/s (or knots). It separates pulse storms from organised multicells from supercells:

<15 m/s — disorganised, single-cell.
15–20 m/s — multicell, squall line potential.
20–25 m/s — supercell-favoured.
>25 m/s — classic supercell territory, and possibly bow echoes if linear.

0–3 km bulk shear matters for MCS longevity and low-level rotation. 0–1 km shear gates tornado potential alongside low-level SRH. In the UK, deep-layer shear is usually there (we're close to the jet); what's often missing is surface-based CAPE at the same time.