National Weather Service United States Department of Commerce

Severe Thunderstorms and Excessive Rainfall in the Central U.S.; Heat Building in the Western U.S.

A cold front pressing east across the central U.S. will be the focus for areas of strong to severe thunderstorms and excessive rainfall through this weekend. Strong to severe thunderstorms my bring damaging winds, hail, and a few tornadoes while excessive rainfall may lead to areas of flooding. Heat will build across the western U.S. with heat-related watches, warnings, and advisories 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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