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Gfs  Storm Relative Helicity                                                   source:http://www.lightningwizard.com

150-300: supercell development possible with large CAPE, risk for weak tornadoes (F0, F1)
300-450: supercell development possible with small CAPE, risk for strong tornadoes (F2, F3)
>450      : large risk for supercell development, risk for violent tornadoes (F4, F5) source:www.theweatherprediction.com

Helicity (HEL) is a mathematical quantity derived from: 1. speed shear (how much wind speed increases with height) between the surface and 3 km above, 2. directional shear (how much wind speed changes direction with height) between the surface and 3 km above, 3. The strength of the low level wind directly into the speed and directional wind shear. The stronger each of these components is the higher the helicity. source: source:www.theweatherprediction.com

When we compute helicity, it is most appropriate to use storm-relative winds. To find the storm-relative wind, we subtract the anticipated or observed storm speed and direction from the wind at every level of the sounding. This process requires a hodograph analysis of the wind profile to predict the storm motion. Several methods have been proposed to determine supercell storm motion. Currently the most accepted approach is the ID method. Generally, storms in an environment with a clockwise-curving hodograph will move to the right of the 0-6 km mean wind, while storms in an environment with a counterclockwise curving hodograph will move to the left.

Automated sounding routines such as the interactive skew-T compute SREH from the hodograph. On the hodograph, SREH is proportional to the area swept out by the storm relative wind vector over the depth of the inflow, typically 3 km AGL, as depicted in this figure. SREH values are positive for right-moving storms, characterized by clockwise-curving hodographs (as shown here) and cyclonic rotation, while SREH values are negative for left-moving, anticyclonic-rotating storms with counterclockwise-curving hodographs.