Australian Rainfall and Temperature Extremes

The data in the extremes listings is provided by the Bureau of Meteorology. The listings carry the following information for each day:

• The five highest reported rain totals in the nation for the 24 hours to 9am local time
• All 24-hour rainfall reports of 50mm or more ordered by location
• Reports of high short-duration rainfall, defined as rainfall over periods ranging from 1 minute to 6 hours. These are taken from the Bureau's automatic weather station network, and from the 3- or 6-hourly synoptic reports provided by about 600 Bureau observers around the country. The reports list the actual rain received and the period over which it was recorded, while the calculated rainfall rate per hour is shown in bold. It's not uncommon for one rainfall event to produce several period totals. A sliding scale is used to determine what reports are included:
  • For periods of 5 minutes or less, the minimum rainfall rate is 80mm/hour
  • Between 6 and 10 minutes, the minimum rate is 40mm/hour
  • Between 11 and 30 minutes, the minimum rate is 20mm/hour
  • Between 31 and 60 minutes, the minimum rate is 10mm/hour
  • For 3 and 6 hour totals, the minimum rate is 5mm/hour
• The absolute highest and lowest maximum and minimum temperatures across the country
• The highest and lowest maximum and minimum temperatures compared to normal i.e. the places recording the greatest departures above and below their normal max and min temperatures. Whilst the same locations in the nation always seem to be highest or lowest (hot in tropical WA and cold in Tasmania and the Snowies!), any station for which averages are available has a pretty even chance of appearing in these columns.
• High winds recorded by automatic weather stations. All wind gusts of 90km/h (storm force) or more are listed, together with the wind direction and the mean wind speed at the time. The mean wind speed is the average over the 10 minutes before the stated time. In addition, any mean wind above 62km/h (gale force) which occurred without reported gusts of 90km/h or more are listed. If the gust speed is shown as "****", it means gust speed not recorded.  Where a station reports several gust or mean speeds above the threshold, only the highest is shown.
• Other extremes. These include the highest recorded flood readings, extreme pressure rises and falls, and any other statistical aberrations that take my fancy.

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.