Synoptic and mesoscale aspects of exceptional fire weather during the New Year period 2019-20 in southeastern New South Wales, Australia

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.