Friday, 31 August 2012 - Seasonal Climate Summary for Perth - Product code IDCKGC11L0

Perth in winter 2012: A warm and very dry winter

  • Rainfall: Very much below average
  • Maximum temperature: Very much above average
  • Minimum temperature: Generally near average
This statement was prepared before all data for the period were available. This may affect some of the statistics presented.

Details Extremes Records Summaries Important notes the top

Rainfall

Rainfall across the Perth metropolitan area during winter 2012 was very much below average at most sites, mainly due to the driest July on record at most locations, with June totals being close to average, and August totals being near average to below average. Winter rainfall totals were generally in the 250 mm to 300 mm range, grading to 400 mm to 500 mm in the Perth hills.

Significant rainfall events during winter 2012 in Perth:

  • A slow moving trough off the west coast, associated with a near stationary low to the southwest of the state, brought showers and thunderstorms with moderate falls to Perth on 6 June. The trough moved gradually eastward over land during the morning of the 7th, with severe thunderstorms developing over Perth in the late morning and early afternoon, and a tornado was reported close to midday in the suburbs of Dianella and Morley, causing substantial damage.
  • A rapidly deepening tropical low off the northwest coast of Western Australia moved south-southeastward close to the west coast during the morning on 10 June and crossed the Southwest district during the afternoon, bringing severe wind gusts and moderate rainfall to the Perth area.
  • A cold front moved through the Perth metropolitan area on 11 June bringing further rainfall and more severe wind gusts before a rapidly developing cold front and deep low pressure system moved through the Southwest Land Division (SWLD) during the afternoon and evening of the 12th, bringing moderate to heavy falls and more severe winds to the Perth area.
  • A persistent westerly flow was maintained over the Perth region from 12 to 18 June, bringing consistent, though generally light, rainfall. Cold fronts on the 19th and 20th brought moderate falls.
  • July 2012 saw only a handful of light rainfall events in the Perth area, with daily rainfall totals generally less than 10 mm.
  • A strong cold front and pre-frontal trough brought moderate to heavy falls to the Perth area on 12 August. Mundaring in the hills received 53.0 mm in 24 hours to 9am on the 13th, the highest daily fall recorded in the Perth metropolitan area during winter 2012.

Perth Metro recorded 262.6 mm of rainfall on 42 rain days during winter 2012, well below the average of 478.7 mm on 48 rain days and was the 4th driest winter on record behind 2006 (230.4 mm), 2010 (256.4mm), and 1940 (260.0 mm). Rainfall records commenced at Perth Metro in 1876. Rainfall totals at Perth Metro for the individual months in winter 2012 were: June: 140.8 mm (average 175.7 mm), July: 34.6 mm (average 169.6 mm), and August 87.2 mm (average 133.4 mm).

Maximum temperature

Mean daily maximum temperatures for winter 2012 were very much above average across the Perth region and in the 18 °C to 20 °C range, with most sites 0.5 °C to 1.0 °C above normal. The very much above average winter mean maxima were the result of slightly above average maxima in June, very much above average maxima in July, with some sites registering a record high July, and an above average August. Consequently, Swanbourne recorded its highest winter mean maximum temperature in 18 years of record.

A high in the Bight directed warm northeasterly winds over the Perth area during early June, and again in mid-August, with all Perth sites observing their warmest winter days on either 3 June or 10 or 11 August. A maximum temperature of 25.5 °C at Gosnellls City on 3 June was the highest temperature recorded in the metropolitan area during winter. The lowest maximum temperature for winter was 11.3 °C at Bickley on 20 June in southerly winds after the passage of a cold front.

Perth Metro's mean daily maximum temperature for winter 2012 was 19.7 °C, which is 0.9 °C above the winter average of 18.8 °C and the equal second warmest winter on record with 1976 and 1983 (comparable temperature records commenced in 1897). Perth Metro's warmest winter was in 2006 when a mean maximum temperature of 19.8 °C was observed.

Minimum temperature

Mean daily minimum temperatures during winter 2012 were generally near average across the Perth region, with mean daily minima close to 8 °C for inland sites, but were generally in the 10 °C to 13 °C range near the coast. The near average winter was the result of an above average June, a very much below average July, with record low mean minima at some sites, and a slightly above average August.

Cool to cold nights were observed throughout most of July 2012, with generally clear skies throughout much of the month. A particularly cold night was observed on the 25th when Perth Airport, Pearce RAAF, and Jandakot Aerodrome registered sub-zero overnight temperatures and most sites observed their coldest night for winter 2012. The mildest night for winter 2012 for a number of metropolitan sites occurred on 3 and 4 June in a northerly flow as a strong low pressure system sat to the southwest of WA. Rottnest Island recorded a minimum temperature of 17.7 °C on the 4th, the highest for winter in the Perth metropolitan area.

Perth Metro's mean daily minimum temperature for winter 2012 was 8.0 °C, which is close to the average of 8.2 °C.

Wind and Sunshine

Perth’s mean daily winter sunshine was 6.5 hours per day in 2012, which is close to the long term average of 6.4 hours per day.

Extremes Records Summaries Important notes the top

Further information

Western Australia Climate Services Centre
Bureau of Meteorology
Phone (08) 9263 2222
Email climatedata@bom.gov.au
Extremes in winter 2012
Hottest day 25.5 °C at Gosnells City on 3 Jun
Warmest days on average 19.9 °C at Gosnells City
Coolest days on average 16.1 °C at Bickley
Coldest day 11.3 °C at Bickley on 20 Jun
Coldest night -1.6 °C at Jandakot Aero on 25 Jul
Coolest nights on average 6.7 °C at Jandakot Aero
Warmest nights on average 13.0 °C at Rottnest Island
9.8 °C at Swanbourne
Warmest night 17.7 °C at Rottnest Island on 4 Jun
15.9 °C at Swanbourne on 21st Jul
Wettest overall 479.4 mm at Mundaring
Wettest day 53.0 mm at Mundaring on 13 Aug
Highest wind gust 119 km/h at Rottnest Island on 10 Jun

Extremes Records Summaries Important notes the top

Record highest winter mean daily maximum temperature
Mean daily maximum
temperature
for winter 2012 (°C) 		Previous warmest
for winter		 Years of
record		 Average for
winter
Swanbourne 19.7 19.6 in 2006 18 18.8


Extremes Records Summaries Important notes the top

Summary statistics for winter 2012
Maximum temperatures
for winter
(°C)		 Minimum temperatures
for winter
(°C)		 Rainfall
for winter
(millimetres)
Mean for
winter
2012		 Diff
from
average		 Highest for
winter
2012		 Mean for
winter
2012		 Diff
from
average		 Lowest for
winter
2012		 Total for
winter
2012		 Average
for
winter		 Rank of
winter
2012		 Fraction of
winter
average
Bickley 16.1 +0.5 21.6 11 Aug 7.8 +0.3 2.9 9 Jul 433.4 592.7 low 73%
Champion Lakes 18.8   23.7 3 Jun 9.5   2.7 25 Jul 285.8
Garden Island HSF 18.4 +0.1 23.1 3 Jun 11.3 -0.1 5.6 13 Jul 267.4 324.4 low 82%
Gosnells City 19.9 +0.8 25.5 3 Jun         263.4 457.8 v low 58%
Jandakot Aero 19.3 +0.9 24.3 10 Aug 6.7 -0.4 -1.6 25 Jul 303.6 461.3 v low 66%
Medina Research Centre 19.5 +0.7 24.5 10 Aug 8.1 -0.4 0.3 25 Jul 286.8 410.5 v low 70%
Pearce RAAF 19.3 +1.0 24.3 11 Aug 7.8 -0.9 -0.8 25 Jul 256.8 374.6 low 69%
Perth Airport 19.5 +1.1 24.5 11 Aug 8.0 -0.3 -0.7 25 Jul 276.4 436.5 v low 55%
Perth Metro* 19.7 +0.9 24.5 11 Aug 8.0 -0.2 0.4 25 Jul 262.6 478.7 v low 55%
Rottnest Island 18.6 +0.5 23.4 3 Jun 13.0 +0.3 9.1 18 Jul 271.6 392.1 v low 69%
Swanbourne 19.7 +0.9 24.7 3 Jun 9.8 -0.2 3.9 25 Jul 310.8 389.9 low 80%

Extremes Records Summaries Important notes the top

Notes

This statement was prepared before all data for the period were available. This may affect some of the statistics presented.

A Seasonal Climate Summary is prepared to list the main features of the weather in Perth using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at 11 am on Friday 31 August 2012. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

Averages are long-term means based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 10 years of record.
The median is sometimes more representative than the mean of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site, based on the decile ranking (very low rainfall is in decile 1, low in decile 2 or 3, average in decile 4 to 7, high in decile 8 or 9 and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a percentage of the long-term mean.

Further information

Western Australia Climate Services Centre
Bureau of Meteorology
Phone (08) 9263 2222
Email climatedata@bom.gov.au