The data in the extremes listings is provided by the Bureau of Meteorology. The listings carry the following information for each day:
Up to 1999, the extremes were presented in a different format. Data for these years will gradually be replaced with data in the new format.
Rainfall and Temperatures
With about 8,000 rainfall stations currently operating in Australia, identification can be a problem. The names given are those provided by the Bureau of Meteorology, and often give additional information to distinguish between stations in the same area (e.g. Dorrigo Post Office and Dorrigo (Old Coramba Road)). Sometimes pastoral property names are given along with their locality (e.g. Craven (Longview)). Use the Australian Place Name Searcher from Auslig to find these places on a map -- you will discover that even most property names are findable.
Rainfall data arrives in two stages:
Real time data from over 2000 rainfall stations is received soon after 9am each day, and I usually post rainfall data the same day. Temperature data is normally posted the following day when the official maximum temp for the previous day is known. All this data is subject to only limited quality control, basically by my running an intelligent eye over it! Whilst almost all of the Bureau's climatic stations report their temperatures daily, only about 25% of the enormous rainfall network reports in real time.
Written returns of rainfall data come into the Bureau by mail after the end of each month. The Bureau then performs quality control checks on all data, whilst thousands of additional rainfall stations' data are entered into Bureau archives for the first time. I try to rerun the data extraction programs to incorporate this data in the extremes a couple of months after real time. These updates reveal many interesting heavy falls. For example, compare the highest rainfall totals for Australia reported in real time for 16 February 1998 with the final list :
Until the additional information for this day came in, the highest reported rain in Tasmania was 56mm at Bicheno on the east coast. The more detailed data reveals that the northeastern slopes of Mount Wellington near Hobart received a major downpour!
The extremes pages also list records set, but these should not be regarded as a definitive listing. They are done in real time, and mistakes are possible and omissions inevitable. For more detailed information on records set during the month, visit the BoM's Monthly Significant Weather descriptions, though even these listings, prepared some months after the event, are heavily qualified. The area of temperature and rainfall records is fraught with difficulty. Visit Blair Trewin's Australian Temperature Extremes site to gain an insight into this.
The data I use is supplied by the Bureau of Meteorology via CMSS landline and the SILO joint initiative, a subscription to which I'd recommend to anyone interested in maintaining detailed, accurate records.