The use of high spatial and temporal resolution data assimilation and forecasting around Australia's capital cities and rural land provides an opportunity to improve moisture analysis and forecasting. To support this endeavour, RMIT University and Geoscience Australia have worked with the Bureau of Meteorology (BoM) to provide real-time GNSS (Global Navigation Satellite System) Zenith Total Delay (ZTD) data over the Australian region, from which a high-resolution total water vapour field for SE Australia can be determined. The ZTD data can play an important role in high-resolution data assimilation by providing mesoscale moisture data coverage from existing GNSS surface stations over significant areas of the Australian continent. The data are now used by the BoM's high-resolution ACCESS-C3 capital city NWP systems, the ACCESS-G3 Global system and have been used by the ACCESS-R2-Regional NWP model. A description of the data collection and analysis system is provided. An example of the application of these local GNSS data for a heavy rainfall event over SE Australia/Victoria is shown using the 1.5km resolution ACCESS-C3 model, which is being prepared for operational use. The results from the test have been assessed qualitatively/synoptically and also have been examined quantitatively using the Fractions Skills Score which shows the reasonableness of the forecasts and demonstrates the potential for improving rainfall forecasts over south-eastern Australia by the inclusion of ZTD data in constructing the moisture field. These data have now been accepted for operational use in NWP.

The relationship between El Niño-Southern Oscillation (ENSO) indices and precipitation (P) in some parts of Australia has previously been shown to be non-linear on annual and seasonal time scales.Here we examine the relationship between P and the Southern Oscillation Index (SOI) at all Australian locations and in all seasons.We show that in many Australian regions, there is more-than-expected P during strong La Niña years (SOI>13), but less-than-expected drying during strong El Niño years (SOI<-13).Statistically significant non-linearities are found over northern NT, QLD and parts of WA during SON, and parts of QLD, NSW, and VIC during DJF, when regressing P against June-December SOI.During the MAM immediately preceding a June-December ENSO year, and during JJA, the rainfall-SOI relationship is linear over most of the country.Systematic eastward shifts in P patterns can explain non-linearities over northern Australia, but do not explain non-linearities southward of approximately 20˚S.The seasonal P distribution is decomposed into FP, the fraction of days on which P falls, and PD, the amount of rain per day on days when P is non-zero.Both FP and PD display a non-linear relationship with SOI similar to the P-SOI relationship, although the relative influence of each term on P is spatially and seasonally dependent.

Southern hemisphere circulation patterns and associated anomalies for austral summer 2015-16 are reviewed, with an emphasis on the tropical Pacific as well as Australian rainfall and temperatures. Following the peak of El Nino in November 2015, summer 2015-16 featured continued near-record El Nino conditions in the tropical Pacific but saw the emergence of cooler subsurface waters in the equatorial Pacific. A moderate Madden Julian Oscillation (MJO) pulse and positive Southern Annular Mode (SAM) ontributed to average to above average rainfall across much of Australia, while the Maritime Continent and parts of far northern Australia saw continued below average rainfall. Sea surface temperatures during summer 2015-16 were the warmest on record for the southern hemisphere oceans, with very warm ocean temperatures in the Indian Ocean and Australian region, including the warmest summer sea surface temperatures on record around Tasmania. Air temperatures were also warmer than normal across Australia throughout the season, with a significant heatwave in southeast Australia during December.

Communicating the development of El Nino and La Nina events is often challenging, largely due to the general misconception that the transition to an event can occur rapidly – like flicking a switch. Additionally, in Australia the association of El Nino with drought, and La Nina with flood, and the impacts that result, can often cloud the message. The Australian Bureau of Meteorology is responsible for issuing updates on the current status of the El Nino-Southern Oscillation (ENSO), and declaring the onset and demise of an event. To assist in the communication of this often complex message, the Bureau of Meteorology developed an online tool, the ENSO Outlook, to keep stakeholders informed of the potential for El Nino or La Nina to develop in the upcoming seasons.

The Waroona bushfire burnt 69,000 ha south of Perth in January 2016. During the first two days of the fire, there were two pyrocumulonimbus (pyroCb) events and two destructive evening fire runs. Over 160 homes were destroyed and there were two fatalities. This case study examines in detail the links between the meteorological observations and the fire behaviour reconstruction. The first pyroCb developed on Wednesday 6 January 2016, when the fire made an unexpectedly fast run in light prevailing winds. The pyroCb produced lightning strikes that ignited a new fire downwind of the main head fire. A second pyroCb developed on Thursday morning, against normal diurnal thunderstorm trends. Similar to the previous evening, the fire spread faster than expected, given the near-surface meteorological conditions. On both evenings there were destructive ember storms over the towns of Waroona (Wednesday) and Yarloop (Thursday). Examination of the meteorological observations has linked these ember showers to the onset of downslope winds, locally known as `scarp winds'. As downslope winds are associated with strong localised turbulence, they provide a mechanism for transport of large numbers of firebrands. The periods of extreme fire behaviour at Waroona were against normal diurnal expectations and did not coincide with the highest observed Fire Danger Index (FDI) values, which occurred at around 1600 LT. This study links both pyroCb events to accelerated fire spread, which presents a hazard to firefighters that is not accounted for in traditional, surface based methods of fire prediction. Downslope winds similar to those that impacted the Waroona fire occur at many locations. They provide a highly localised mechanism for destructive evening ember showers. This investigation into the Waroona fire describes the potential impacts of fireatmosphere feedback processes. Consequently, it highlights the need for predictive methods and tools that anticipate fire behaviour which is not steady-state. Planned simulations using a coupled fire-atmosphere model will allow further insights into features of this case study.