National Weather Service United States Department of Commerce

Winter Storm for south-central U.S.; Critical Fire Weather in the West; Tracking Zeta

Heavy snow will continue to spread south along the Rockies through Monday. An area of freezing rain and sleet is forecast to develop over portions of the southern Plains to start the week. Meanwhile, dry and gusty conditions will continue critical fire weather conditions from California into southern New Mexico. Zeta is forecast to become a hurricane tracking north across the Gulf of Mexico. 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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