Australian Monthly Climate Summary: December 2006
Wednesday 3rd January, 2007
December 2006 in Australia saw few large departures from normal in either rainfall or temperature. Nationally averaged maximum and minimum temperatures were both very close to the 1961−90 normal, with anomalies of −0.01°C (23rd highest since 1950) and +0.06°C (27th highest since 1950) respectively. Nationally-averaged rainfall was 24% below normal, the fifth successive month of below-normal rainfall, but less so than the four previous months.
Maximum temperatures were above normal in the northern tropics. Anomalies reached +2°C on Cape York Peninsula, which made it the warmest December on record in that region, whilst widespread anomalies near +1°C along the northern coast were in the warmest 10% of recorded years. Other warm areas were the west coast of Western Australia from Carnarvon southwards (with anomalies of +2 to +3°C around Shark Bay and south of Perth), and much of the southeast (anomalies generally +1 to +2°C). Elsewhere maxima were below normal, particularly in parts of southern Queensland (1−2°C below average) and over most of the Northern Territory apart from the far north.
Minimum temperatures were close to normal through most of the country with almost everywhere within 2°C of average. The most significant cool area was in south-eastern Queensland and north-eastern New South Wales, where minima were in the coolest 10% of all Decembers with anomalies around −1°C. It was also rather cool in Victoria, Tasmania and the south-east of South Australia, although anomalies only locally reached −1°C. Conversely, anomalies around +1°C occurred on the west coast of Western Australia, as well as along the western slopes of the Great Dividing Range in New South Wales, in south-west Queensland and the south-east of the Northern Territory.
One of the most severe December cold outbreaks of the last 50 years affected the south-east over the Christmas period, in stark contrast to the very warm conditions earlier in the month. There was substantial snow (up to 20 centimetres in places) above 800 metres in Tasmania and above 1000−1200 metres in Victoria and southern New South Wales, whilst snow fell (but did not settle) on Christmas morning in the Dandenong Ranges, on the outer fringe of Melbourne. Mount Buller, which was seriously threatened by fire for much of the month, set a new Australian record low maximum for December with a top of only −0.8°C on Christmas Day, whilst Mount Baw Baw (−0.4°C) also broke the previous record and Thredbo (0.1°C) set a New South Wales record.
* Anomaly is the difference from the long-term average
It was a generally dry month in south-eastern Australia, although rain in the last ten days of the month prevented it from being an exceptionally dry one. Victoria had its ninth-driest December on record (67% below normal), while Tasmania and New South Wales were 45% and 54% below average respectively. A number of areas had December rainfall in the driest 10% of all years, the most substantial being in eastern and south-western Victoria, and north-eastern Tasmania. It was also rather dry in south-eastern Queensland and north-eastern New South Wales. Another substantial area of dry conditions was the Cape York Peninsula in northern Queensland, where a delayed start to the wet season saw low December records set in a few locations.
Lightning strikes from thunderstorms started more than 100 fires in north-eastern Victoria on the evening of 1 December. With the extremely dry lead-up conditions (most of the area had its driest eleven months on record from January to November), some of these fires spread and ultimately merged into a single fire. Fire intensity and spread lessened from the 22nd onwards after rain and snow fell on the area, but the fire was still burning, largely within containment lines, at the end of the month. The total area burnt by 31 December was approximately 9,000 square kilometres.
It was a wet month in much of the interior of Western Australia, with a few areas in the wettest 10% of all Decembers. Through most of the remainder of the tropics and sub-tropics (including the Northern Territory, inland Queensland and northern South Australia), rainfall was generally close to normal, but with wide variations over short distances (both above and below) because of thunderstorm activity (or its absence thereof).