SRH — Storm Relative Helicity

SRH is a vertically integrated measure of streamwise vorticity relative to a storm's motion vector. Practically it's the area swept out on a hodograph between two heights, relative to storm motion, expressed in m²/s².

Common layers and thresholds:

• 0–1 km SRH > 150 m²/s² — significant tornado-favoured.
• 0–3 km SRH > 250 m²/s² — strong rotation potential for supercells.
• Under 100 m²/s² — broadly non-rotational.

In UK summer, 0–1 km SRH values above 200 are rare but correlate strongly with our handful of historical tornadic supercells. Winter extratropical systems produce comparatively larger helicity but in cold, low-CAPE regimes — rotation without buoyancy.