Tuesday, 4 January 2011 - Monthly Climate Summary for New South Wales - Product code IDCKGC35R0

New South Wales in December 2010: Cold, wet start to Summer

• 8th wettest December on record for NSW.
• 2nd wettest December on record for the MDB.
• 5th coldest December on record for NSW (maximum temperatures).
• 6th consecutive month with above average rainfall in NSW.

Extremes Maps Records Summaries Important notes the top

Rainfall

NSW experienced a wet start to summer, under the continued influence of the strong La Niña event in the Pacific Ocean. This was the 6th consecutive month with above average rainfall for NSW - a response consistent with patterns typically expected during a La Niña event. The statewide average rainfall for the month was 95.6 mm which is well above the historical average¹ of 54.2 mm. This is the wettest December since 2007, when 106.6 mm was recorded, and the 8th wettest December on record for NSW (records since 1900). Additionally, this is the 4th consecutive December with above average rainfall for NSW.

The Murray Darling Basin also recorded above average rainfall, with a basin-wide average of 104.12 mm which is more than double the historical average of 48.8 mm, and significantly wetter than December 2009 (76.2 mm). This was the 2nd wettest December on record for the MDB (records since 1900), following the record rainfall of 120.7 mm set in 1992.

Thirty-three stations recorded their wettest December on record this month, with an additional 45 recording their wettest since at least the 1980s. Rainfall was highest along the Ranges and Tablelands, with large areas experiencing their highest totals on record, while very much above average falls were also recorded along the southwestern and northeastern borders. The most significant rainfall occurred during the first ten days of the month, particularly over southern and western regions, resulting in widespread flooding. However, the highest daily totals anywhere in the state occurred on Christmas Day, with rainfall reaching 155mm at Mullumbimby in northeastern NSW.

Some sites had their highest total December rainfall on record.
See a map of rainfall deciles.

Temperature

Day-time temperatures were significantly cooler than average during December, marking the 5th consecutive month with below average maximum temperatures for NSW. The statewide average maximum temperature for the month was 28.4°C, which is 2.2°C below the historical December average¹ of 30.6°C. This is the coolest December since 1999 in NSW (28°C), and the 5th coolest on record. Additionally, seven stations across NSW recorded their lowest December mean maximums on record during the month. The below average day-time temperatures experienced across NSW is consistent with the pattern typically expected during a La Niña event. However, warm sea surface temperatures off the NSW coast associated with the La Niña event resulted in warm temperatures at the offshore islands, including the warmest December day on record at Norfolk Island on the 28th.

Statewide average minimum temperatures were also slightly below average during the month at 15.9°C, which is 0.2°C below the historical average of 16.1°C. This is the coolest December since 2001 (15.5°C) for minimum temperatures in NSW. Minimum temperatures varied considerably across the state, with above average minimums in eastern NSW but below average minimums in the west, including record cold nights at nine stations. Nights were particularly cold on the 20th and 21st, with temperatures up to 12°C below average in central NSW and record cold at nine stations.

The statewide average mean temperature for December was 22.1°C, which is 1.2°C below the historical average of 23.3°C. This is the coolest December since 1999 for statewide average mean temperatures, and the 10th coolest December on record.

Some sites had their highest December temperature on record.
Some sites had their lowest December mean daily maximum temperature on record.
See a map of maximum temperature anomalies.

Some sites had their lowest December temperature on record.
Some sites had their warmest December night (highest daily minimum temperature) on record.
See a map of minimum temperature anomalies.

Other phenomena

A deep low pressure system over the Tasman Sea was responsible for a significant cold snap from the 19-21st December. Minimum temperatures were up to 5 degrees below average across many parts of NSW, and snow was observed on the Snowy Mountains.

Heavy rain during the last week of November and first weeks of December lead to substantial flooding during early December, with widespread evacuations of towns including Wee Waa, Coonamble, Queanbeyan and Wagga Wagga. The Burrinjuck and Captains Flat dams were in danger of failure, with 135 flood rescues and over 2800 requests for assistance to the SES between November 29 and December 13. Forty-one individual shires across the state had Natural Disasters declared during early December, with major infrastructure damage in key rural centres including Orange, Dubbo, Wagga Wagga and Tamworth. Reports suggested this was the most severe flooding in 50 years in some regions. This was further exacerbated in late December by rainfall in northern NSW and Queensland, which progressed down river systems during late December and early January and resulted in 700 further requests for assistance between the 13th and 29th of December.

Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top