National Weather Service United States Department of Commerce

Snow Across the Great Lakes, Central Appalachians, and Northeast; Unsettled Weather in the West

Light to moderate snow will continue into Saturday over the Great Lakes, Central Appalachians, and Northeast. This weekend into next week, a series of atmospheric rivers will bring gusty winds, periods of heavy rain, and mountain snow to northern California and the Pacific Northwest. Colder temperatures are in store for the weekend from the Great Lakes to East Coast. 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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