Tuesday, 3 January 2012 - Monthly Climate Summary for Western Australia - Product code IDCKGC31R0

Western Australia in December 2011: Third wettest December for southwest WA

• Rainfall: Near average for WA; 3rd wettest December for southwest WA.
• Maximum temperature: Near average.
• Minimum temperature: Near average for WA; 4th warmest for southwest WA.

Details Extremes Records Summaries Important notes the top

Rainfall

Rainfall in WA during December 2011 was above to very much above average for most of the Southwest Land Division (SWLD), adjacent parts of the Goldfields, and the southeast Gascoyne, with numerous sites in the SWLD (many with over 100 years of record) registering their wettest December on record, mainly due to extremely heavy rainfall events on the 6th and 12th. Above to very much above average rainfall was also observed in the Interior and inland Kimberley, where the highest rainfall totals for December in WA were recorded, and the coastal Eucla, while below to very much below average rainfall was evident through much of the Pilbara and northwest Gascoyne, the coastal Kimberley, and inland Eucla (see the December 2011 rainfall totals & deciles maps).

When averaged across the state, December 2011 rainfall was near average, however for both the SWLD and the Lower Southwest (southwest a line from Jurien Bay to Bremer Bay), December 2011 ranked as 3rd wettest on record. Comparative rainfall records commenced in 1900.

A deep middle level trough off the west coast produced the first significant summer rainfall in the SWLD and the adjacent Goldfields and Gascoyne on the 6th. Numerous sites in the Lower West, Central Wheat Belt, and Great Southern observed over 50 mm during the event, though the heaviest downpours occurred in the eastern Central Wheatbelt and northeast Great Southern. Daily rainfall totals of 109.0 mm at Amrista Park and 105.0 mm at Hyden, both in the northeast Great Southern, in the 24 hours to 9am on the 7th were not only their wettest December days on record, but also their highest daily rainfall total for any month, and in the top ten highest December daily falls on record in the SWLD. Many other sites in the SWLD also broke their previous wettest December day on record on the 7th.

Another deep mid-level trough off the west coast brought further widespread moderate to heavy rainfall across the SWLD and the adjacent Goldfields and Gascoyne on the evening on the 12th and into the morning of the 13th, with numerous sites in the SWLD and Gascoyne observing their highest December daily rainfall on record. Areas in the Great Southern were hit hardest by the downpour, and the daily total of 125.6 mm at Williams in the Great Southern in the 24 hours to 9am on the 13th was not only their wettest December day in 115 years of record, but also the highest daily rainfall recorded in December in the SWLD. For more details of these two extreme heavy rainfall events, please see Special Climate Statement 35.

Maximum temperature

Mean daily maximum temperatures in WA during December 2011 were below to very much below average over eastern parts of the SWLD, the Goldfields, western Eucla, and southern Interior, with areas up to 3 °C cooler than normal in the southern Interior, eastern Goldfields, and far western Eucla. Below average daytime temperatures were also observed in coastal parts of the Pilbara, despite extremely hot days in the week prior to Christmas with temperatures in the high 40s. Above to very much above average maxima were observed along the west coast of WA, extending into the northern Gascoyne and inland Pilbara. Western and northern parts of the Kimberley also saw above average mean maxima, with temperatures up to 3 °C above normal (see the December 2011 mean maximum temperature deciles & anomaly maps) recorded around King Sound in the Kimberley, and Shark Bay in the Gascoyne.

When averaged across WA as a whole, daytime temperatures were near average for December 2011.

Extremely hot weather was observed in the Pilbara from the 20th through to the 25th, with numerous sites observing daily maxima over 47 °C, and several sites registering record high December temperatures. The December maximum temperature record for WA was also broken on three consecutive days, with Roebourne (49.4 °C on the 21st), Roebourne Airport (49.0 °C on the 21st), Onslow (49.2 °C on the 22nd), and Learmonth Airport (48.9 °C on the 23rd), all surpassing the previous December record of 48.8 °C set at Mardie on 26 December 1986. To further illustrate the significance of the event, Roebourne's 49.4 °C was the 2nd hottest December day on record in Australia, just 0.1 °C below the 49.5 °C recorded at Birdsville in Queensland on 24 December 1972, and the 5th hottest day on record in WA. Sites in WA have recorded temperatures of over 48 °C during December on 18 occasions, and 10 of those occurred during this event.

Minimum temperature

Mean daily minimum temperatures in WA in December 2011 were above to very much above average over large parts of western and southern WA, as well as in the west Kimberley, with up to 3 °C warmer than normal mean minima in the southwest Gascoyne, Central West, and Lower West. Several sites in western parts of the SWLD registered record high December mean minima, including Donnybrook in the Southwest, which has 105 years of record. Broome Airport also recorded its warmest December nights in 72 years of record. Below to very much below average overnight temperatures were reported in the central and southeast Kimberley, and northern and central Interior, with a small patch of up to 3 °C cooler than normal minima in the central Interior (see the December 2011 minimum temperature deciles & anomaly maps).

When averaged across the state, overnight temperatures in WA in December 2011 were below average, however, the Lower Southwest observed its 4th warmest December on record. Comparable temperature records commenced in 1950.

Hot nights were observed in the inland Pilbara from the 20th through to the 26th, with several sites observing minimum temperatures over 30 °C after extremely hot days. Wittenoom observed the hottest night for December 2011 with 33.2 °C on the 22nd, closely followed by Paraburdoo with 33.0 °C on the 26th.

Other Phenomena

Heavy rainfall and thunderstorms on the 6th caused flash flooding, flooded roads, fallen trees and minor damage to homes in Perth and Northam.

Thunderstorms and flash flooding occurred across parts of the SWLD, including the Perth Metropolitan area on the 12th. In the Great Southern region, there was significant flooding in Williams and Narrogin with homes and roads flooded. There were also reports of minor damage to roofs, fallen trees on homes, cars and fences.

Extremes Records Summaries Important notes the top

Extremes Records Summaries Important notes the top

Extremes Records Summaries Important notes the top