Upper level aspects of snowstorms that can change the strength of the vertical motion or moisture transport into a system
large changes in amplitudes between trough and downstream ridge accompanied cyclogenesis (this increases south to north moisture transport
all marked decrease in half-wavelength between the trough axis and downstream ridge indicative of self-development process (increases vorticity, upper level divergence and promotes cyclogenesis)
a trough that becomes diffluence and takes on a negative tilt. (increases upper level divergence and promotes cyclogenesis)
phasing of multiple vorticity maxima observed in about half the cases
a vorticity max that is moving east-northeast. (such movements suggests that the system will have more moisture available than a vort that is moving to the east southeast (this is especially true in the Plains)
Adapted from Kocin and Uccellini, 1990