A synoptic climatological classification of winter precipitation in Victoria

The major synoptic types responsible for Victoria's winter (June-September) precipitation are described, and their relative contribution to rainfall in different geographical areas of the State assessed using a five-station pluviograph network. Five distinct synoptic types are recognised: (a) cold frontal systems interacting with cloud masses of low latitude origin (I fronts); (b) frontal systems not interacting with low latitudes (NI fronts); (c) post-frontal; (d) cold lows; (e) warm lows. The relative contribution of each type varies substantially around the State: individual types tend to be most significant in areas with a relatively good exposure to low-level winds accompanying the system, while their influence is reduced in areas leeward of topographical barriers. The majority of rainfall in northern Victoria is contributed by I fronts, and in eastern Victoria, by cold (cut-oft) lows. Rainfall in southern Victoria has more varied origins but with the exclusively mid-latitude types, NI fronts and post-frontal, assuming greater significance than elsewhere. In particular, the post-frontal type becomes important in hilly locations exposed to the west-southwest. Attempts are made to explain the rainfall distributions associated with the various synoptic types by drawing analogies with northern hemisphere field-studies on orographic precipitation modification.