National Weather Service United States Department of Commerce

Excessive Rainfall in the Southern Plains; Extreme Heat Coming to the Southwest U.S.

Heavy to severe thunderstorms may bring areas of excessive rainfall and flooding over parts of the southern Plains through Friday. A Slight Risk of excessive rainfall has been issued. Dangerously hot temperatures are forecast across parts of southern Arizona and far southeastern California Saturday through Monday. An Extreme Heat Watch has been issued. Read More >

Automatically generated image showing areas of energy helicity index.

 

Thumbnail of an automatically generated image showing areas of energy helicity index. Thumbnail of an automatically generated image showing areas of energy helicity index. Thumbnail of an automatically generated image showing areas of energy helicity index.
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EHI 

The Energy Helicity Index (EHI) is a number which represents the combination of instability and storm relative helicity.  Our 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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