Synoptic and Mesoscale Aspects of Exceptional Fire Weather during the New Year Period 2019–20 in Southeastern New South Wales, Australia

Abstract Extreme fire weather and fire behavior occurred during the New Year’s Eve period 30–31 December 2019 in southeast New South Wales, Australia. Fire progressed rapidly during the late evening and early morning periods, and significant extreme pyrocumulonimbus behavior developed, sometimes repeatedly in the same area. This occurred within a broader context of an unprecedented fire season in eastern Australia. Several aspects of the synoptic and mesoscale meteorology are examined, to identify contributions to fire behavior during this period. The passage of a cold front through the region was a key factor in the event, but other processes contributed to the severity of fire weather. Additional important features during this period included the movement of a negatively tilted upper-tropospheric trough, the interaction of the front with topography, and the occurrence of low-level overnight jets and of horizontal boundary layer rolls in the vicinity of the fireground. Significance Statement Wildfires and the weather that promotes their ignition and spread are a threat to communities and natural values globally, even in fire-adapted landscapes such as the western United States and Australia. In particular, savanna in the north of Australia regularly burns during the dry season while forest and grassland in the south burn episodically, mostly during the summer. Here, we examine the weather associated with destructive fires that occurred in southeast New South Wales, Australia, in late 2019. Weather and climate factors at several scales interacted to contribute to fire activity that was unusually dangerous. For meteorologists and emergency managers, case studies such as this are valuable to highlight conditions that may lead to future similar events. This case study also identified areas where improvements in fire weather service can be made, including the incorporation of more detailed weather information into models of fire behavior.