Supercell Potential (EHI) Forecast
According to the National Weather Service (NWS), the Energy Helicity Index (EHI) is a number which represents the combination of instability and storm relative helicity. The calculation uses mixed layer CAPE (surface to 3000ft average parcel) and 0-3 km storm relative helicity. Values greater than 2 or 3 have been correlated to cyclonic supercells with increased tornadic potential. Negative values are indicative of an environment favorable for anti-cyclonic (left moving) supercells, but tornadoes associated with anti-cyclonic supercells are extremely rare.
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