Skip Navigation Links weather.gov 
NOAA logo-Select to go to the NOAA homepage
National Oceanic and Atmospheric Administration's   
  Select to go to the NWS homepage
National Weather Service   
 
 
Local forecast by
"City, St"
USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.

  Home > Glossary

 
Energy Helicity Index
An index that incorporates vertical shear and instability, designed for the purpose of forecasting supercell thunderstorms
Helicity
A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity). Atmospheric helicity is computed from the vertical wind profile in the lower part of the atmosphere (usually from the surface up to 3 km), and is measured relative to storm motion. Higher values of helicity (generally, around 150 m2/s2 or more) favor the development of mid-level rotation (i.e. mesocyclones). Extreme values can exceed 600 m2/s2.

You can either type in the word you are looking for in the box below or browse by letter.

Search:

Browse by letter:

#  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  

 

 

    US Dept of Commerce
    National Oceanic and Atmospheric Administration
    National Weather Service
    1325 East West Highway
    Silver Spring, MD 20910
    Page Author: NWS Internet Services Team
Disclaimer
Information Quality
Credits
Glossary
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities
     Page last Modified: 25 June, 2009 1:01 PM