National Weather Service United States Department of Commerce

Snow in the Great Lakes; Windy Conditions in the East

Lake effect snow will impact the Great Lakes region through the day. Gusty winds will pick up across the Midwest, Northeast and Mid-Atlantic beginning this afternoon following a cold front. Elevated fire weather conditions will persist across the Desert Southwest today, with critical fire weather conditions developing Wednesday and Thursday in the Southern Plains. 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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