National Weather Service United States Department of Commerce

Dangerous Heat in the West; Coastal Flooding & High Rip Current Risk through the Weekend on the East Coast; Flash Flooding Concerns in the Southeast and Southwest

A dangerous, record heat wave continues across portions of the West through Tuesday. High rip current risk and dangerous surf continue through the weekend. There are flash flooding concerns through the weekend for portions of the Southeast and Southwest. 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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