Springtime fire weather in Tasmania, Australia: two case studies

A number of severe springtime fire weather events have occurred in Tasmania, Australia, in recent years. Two such events are examined here in some detail, in an attempt to understand the mechanisms involved in the events. Both events exhibit strong winds and very low surface dewpoint temperatures. Associated 850-hPa wind–dewpoint depression conditions are extreme in both cases, and evaluation of these quantities against a scale of past occurrences may provide a useful early indicator of future severe events. Both events also feature the advection of air from drought-affected continental Australia ahead of cold fronts. This air reaches the surface in the lee of Tasmanian topography by the action of the fo¨ ehn effect. In one event, there is good evidence of an intrusion of stratospheric, high potential vorticity (PV), air, supplementing the above mechanism and causing an additional peak in airmass dryness and wind speed.