National Weather Service United States Department of Commerce

East Coast Storm; Heavy Rain and Flooding in the Southwest U.S.; Typhoon Remnants Impacting Alaska

A coastal storm continues to bring heavy rain, coastal flooding, high surf, dangerous rip currents, and gusty winds to the East Coast into early Tuesday. A heavy rain and flash flood risk continues for the Southwest/Four Corners region with lingering tropical moisture through Monday. Typhoon remnants are causing strong winds, heavy rain, and coastal flooding across western Alaska through Monday. 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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