High pressure and low-level cold air were retreating in this case. In the other two cases, the cold air was advancing south at low-levels.
Strong (20-40 kt) ageostrophic northerly flow was forecast below 900 mb in all cases, associated with strong low-level frontogenesis.
Negative EPV was diagnosed above a sloping frontal zone, indicating the potential for slantwise convection, as was the case on April 4, 2003.
By far, the heaviest icing occurred at higher elevations, as was the case with the other two events.