The Moist Potential Vorticity (MPV) of a severe snowstorm process during 2015 in Nanjing was diagnostically analyzed the firstly, and then, 57 heavy snow cases during 2008 to 2015 were studied to conclude the relationship between snow accumulation efficiency and 2-meter temperature. Results showed that the barotropic item oMPV has good agreement with snowfall intensity. The snowfall area was well forecasted by combining the baroclinic item of MPV and the surface temperature, and the heavy snowfall area was well corresponding with the large value center of the baroclinic item of MPV. The snow accumulation efficiency was closely determined by surface 2-meter temperature. Their relationship, temperature and snowfall amount could be used to forecast the snowfall depth.