National Weather Service United States Department of Commerce

Areas of Extreme Heat and Excessive Rainfall Potential

Dangerous and extreme heat will remain across portions of the central U.S. this week, persisting across the mid to lower Mississippi Valley, Gulf Coast, southern Plains and portions of Texas. A heat wave over the Southwest U.S. will peak this weekend. Heavy to excessive rainfall may produce flash flooding from the Delmarva Peninsula north into the Hudson Valley today and tonight. 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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