http://w1.spc.woc.noaa.gov/exper/mesoanalysis/help/help_srh1.html
In V5.2.0, the wrf_helicity function was added to calculate this quantity.
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wrf_helicity_1.ncl:
This script shows how to calculate helicity and create a smoothed
contour plot over a map.
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NCL Graphics: WRF Helicity
SRH (Storm Relative Helicity) is a measure of the potential for
cyclonic updraft rotation in right-moving supercells, and is
calculated for the lowest 1-km and 3-km layers above ground
level. There is no clear threshold value for SRH when forecasting
supercells, since the formation of supercells appears to be related
more strongly to the deeper layer vertical shear. Larger values of
0-3-km SRH (greater than 250 m**2/s**2) and 0-1-km SRH (greater than
100 m**2/s**2), however, do suggest an increased threat of tornadoes
with supercells. For SRH, larger values are generally better, but
there are no clear "boundaries" between non-tornadic and significant
tornadic supercells.
wrf_helicity_1.ncl:
This script shows how to calculate helicity and create a smoothed
contour plot over a map.
Dr. Craig Mattocks of the Center for Environmental Modeling for Policy Development, UNC-Chapel Hill contributed this example.