Parameters & indices#composite#tornado

EHI — Energy Helicity Index

Also: EHI

At a glance

A simple product of CAPE × helicity that rolls 'enough energy' and 'enough spin' into one number. Higher is more tornadic.

Deep dive

EHI = (CAPE × SRH) / 160 000, using the 0–1 km (low-level EHI) or 0–3 km (deep EHI) layers.

Thresholds:

EHI < 1 — tornadoes possible but unlikely.
1–2 — favoured for weak-to-moderate tornadoes.
2–5 — significant tornado potential.
>5 — historic / outlier environments.

EHI is the ancestor of the STP; STP adds LCL height and bulk-shear terms and is generally preferred now. EHI still shows up in mesoanalysis displays because it's computationally cheap.