National Weather Service United States Department of Commerce

Powerful Pacific System Impacting the West; First Significant Snow for Portions of the East

Power Pacific system will continue to bring significant impacts for Pacific Northwest into northern California the remainder of the week. Dangerous coastal affects, heavy rain, flooding, strong winds, and higher elevation mountain snow continues. Meanwhile, a storm across the east is set to bring the first accumulating snow to many higher elevations of the Catskills into the central Appalachians. 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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