Perth in winter 2011: An average winter

  • Rainfall: Mostly near average.
  • Maximum temperature: Near average.
  • Minimum temperature: Above average.

Rainfall

Rainfall across the Perth metropolitan area during winter 2011 was generally near average, with cold fronts bringing consistent rainfall for much of the season, particularly during the end of June to early August period. A number of sites observed their wettest winter since 2000 and Bickley's winter total of 672.2 mm was the wettest metropolitan location for winter 2011.

Significant rainfall events for winter 2011 in Perth:

  • A strong cold front produced moderate to heavy rainfall at the start of June, with daily rainfall totals of 20 to 40 mm recorded in the 24 hours to 9 am on the 2nd on the mainland. Some damage was reported in Perth, mainly due to flash flooding.
  • A strong cold front brought heavy rainfall in the late afternoon of 24 June through to the early morning of 25 June, with many sites registering daily rainfall totals in the 50 to 60 mm range. As a result, flash flooding caused some property damage. Swanbourne recorded 32.6 mm in 30 minutes (between 1745 WST and 1814 WST) on the 24th, which equates to a 1 in 50 to 1 in 100 year event, whilst Swanbourne's 24 hour rainfall total of 63.8 mm to 9 am on the 25th exceeded the previous highest daily total for June in 18 years of record (53.0 mm on 4 June 2002).
  • A pre-frontal trough and cold front, followed by unstable westerly winds produced persistent rainfall from 30 June to 3 July, with daily rainfall totals of 20 to 40 mm recorded in the Perth metropolitan area in the 24 hours to 9 am on 1 July.
  • Rottnest Island received an exceptionally heavy fall from a thunderstorm with daily total of 66.8 mm on 21 July, the third highest July daily rainfall recorded at Rottnest Island, and the highest daily total in the Perth area for the month. The rain gauge recorded 32.2 mm between 9:30pm and 10:00pm, which equates to a 1 in 50 to 1 in 100 year event.
  • Flash flooding occurred at Fremantle on 22 July and several cold fronts and a low pressure system produced more downpours and windy weather at the last few days of July which resulted in Jarrahdale observing 72.8 mm, the highest daily rainfall total for winter 2011 in the Perth metropolitan area.
  • A strong front moved across Perth on 21 and 22 August with heavy rainfall observed at a number of locations. Mundaring observed 59.2 mm in the 24 hours to 9am on the 22nd while Jarrahdale observed 54.8 mm and Bickley 52.6 mm on the same day. Minor roof, ceiling and flood damage was reported in several suburbs.. Minor roof, ceiling and flood damage was reported in several Perth suburbs.

Perth Metro recorded 447.6 on 49 rain days during winter 2011, which is close to the long term average of 479.0 mm on 58 rain days. Based on rainfall data only from the Perth Metro (Mount Lawley) site where records commence in 1993, the winter average is 407.1 mm, suggesting that winter 2011 was above average when compared to recent years. Rainfall totals for individual months this winter were: June 171.4 mm (average 175.7 mm), July 161.0 mm (average 169.7 mm), and August 115.2 mm (average 133.6 mm). Last winter (2010). Perth Metro recorded 256.4 mm on 30 rain days, which was the 2nd driest winter on record. The wettest day during winter 2011 was 57.0 mm on 25 June 2011, which was the wettest day in June for 25 years since 77.0 mm was recorded on 25 June 1986.

Maximum temperature

Mean daily maximum temperatures were near to or above average across Perth during winter 2011. Perth metropolitan sites were between 0.3 °C and 1.0 °C above normal, with mean maxima typically between 18.5 °C and 19.5 °C.

A particularly warm day was experienced as winds turned northerly on 21 August ahead of a strong cold front, with most sites observing their warmest day for the season, and Gosnells City observing the warmest day for winter 2011 in Perth with 27.5 °C.

Bickley observed the coldest day of the season with a daily maximum temperature of 9.6 °C on 11 July, its coldest July day in 18 years of record, and the culmination of the coolest week of winter across metropolitan Perth. Bickley was also the coolest location in terms of daytime temperatures, with an average of 16.1 °C across the three months, some 2.2 °C cooler than Rottnest Island which was second coolest.

Perth Metro's mean daily maximum temperature in winter 2011 was 19.3 °C, which was the equal 8th warmest winter on record, equal with 1987, and the warmest winter since 19.5 °C was recorded in 2007. The winter average is 18.8 °C, while Perth Metro's warmest winter was 19.8 °C in 2006. Daily maxima across winter ranged from a cold 13.0 °C on 11 July to a warm 26.3 °C on 21 August. Perth Metro recorded four cold days (a cold day is when the maximum temperature is 15°C or less) during winter 2011, which is equal to the average.

Minimum temperature

Minimum temperatures across Perth during winter 2011 were near to or above average, with all sites between 0.5 °C and 1.3 °C above average. Mean minima were between 8.3 °C and 10.5 °C for most mainland sites.

Jandakot observed its warmest July night in 22 years of record with a daily minimum of 15.1 °C on the 31st as a result of mild northwesterly winds. Conversely, a run of cold nights was experienced during early July 2011, with most sites observing their coldest winter night during this period. Jandakot Aerodrome recorded the coldest night for winter 2011 in the Perth metropolitan area with -0.4 °C on 4 July.

Perth Metro's mean daily minimum temperature in winter 2011 was 9.2 °C, above the average of 8.1 °C, and Perth Metro's warmest winter since 9.7 °C was recorded in 1996. Daily minima across winter 2011 ranged from a cold 1.3 °C on 4 July to a warm 15.4 °C on 31 July. Perth Metro recorded a total of 15 cold nights (minimum temperature of 5 °C or less) during winter 2011, which is the least amount of cold nights for winter since 15 were recorded in 2007. Last winter, Perth Metro recorded its equal greatest number of cold nights with 37.

Wind and Sunshine

A number of cold fronts crossed the Perth region during winter 2011 bringing severe wind gusts. The end of July and beginning of August saw particularly windy conditions due to a deep low to the south of the state and cold fronts embedded in a westerly flow crossing Perth. Rottnest Island observed the strongest gust for the season during this period with 126 km/h on 27 July.

Perth's average daily sunshine hours during winter 2011 was 6.3 hours, close to the average of 6.4 hours.

Further information

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Extremes in winter 2011
Hottest day 27.5 °C at Gosnells City on 21 Aug
Warmest days on average 19.8 °C at Gosnells City
Coolest days on average 16.1 °C at Bickley
Coldest day 9.6 °C at Bickley on 11 Jul
Coldest night -0.4 °C at Jandakot Aero on 4 Jul
Coolest nights on average 8.3 °C at Jandakot Aero
Warmest nights on average 13.2 °C at Rottnest Island
Warmest night 17.3 °C at Rottnest Island on 21 Aug
Wettest overall 672.6 mm at Bickley
Wettest day 72.8 mm at Jarrahdale on 31 Jul
Highest wind gust 126 km/h at Rottnest Island on 27 Jul

Highest total winter rainfall for at least 10 years
Total rainfall
for winter 2011 (mm)
Most recent winter
this high or higher
Years since
higher
Average for
winter
Medina Research Centre 420.2 530.1 in 2000 11 414.7
Perth Airport 436.4 442.2 in 2000 11 438.9
Swanbourne 444.6 445.6 in 2000 11 394.3
Jandakot Aero 520.4 603.2 in 2000 10 465.6




Summary statistics for winter 2011
Maximum temperatures
for winter
(°C)
Minimum temperatures
for winter
(°C)
Rainfall
for winter
(millimetres)
Mean for
winter
2011
Diff
from
average
Highest for
winter
2011
Mean for
winter
2011
Diff
from
average
Lowest for
winter
2011
Total for
winter
2011
Average
for
winter
Rank of
winter
2011
Fraction of
winter
average
Bickley 16.1 +0.5 23.2 21 Aug 8.4 +0.9 3.0 5 Aug 672.6 596.4 high 113%
Champion Lakes 18.5   25.3 21 Aug 10.5   3.8 4 Jul 357.2
Garden Island HSF 18.5   24.1 21 Aug 12.2   7.4 4 Jul 374.0 330.1 high 113%
Gosnells City 19.8 +0.7 27.5 21 Aug     4.8 10 Jul 441.7 461.9 average 96%
Jandakot Aero 19.3 +0.9 26.2 21 Aug 8.3 +1.3 -0.4 4 Jul 520.4 465.6 average 112%
Medina Research Centre 19.4 +0.6 25.4 21 Aug 10.0 +1.6 1.3 4 Jul 420.2 414.7 average 101%
Pearce RAAF 18.9 +0.6 25.6 21 Aug 9.4 +0.7 0.7 4 Jul 291.6 375.7 low 78%
Perth Airport 19.4 +1.0 27.0 21 Aug 9.1 +0.8 0.2 4 Jul 436.4 438.9 average 99%
Perth Metro 19.3 +0.5 26.3 21 Aug 9.2 +1.2 1.3 4 Jul 447.6 479.0 average 93%
Rottnest Island 18.3 +0.3 22.5 21 Aug 13.2 +0.6 9.2 3 Jul 359.2 392.1 average 92%
Swanbourne 19.4 +0.7 24.5 21 Aug 10.8 +0.8 4.7 4 Jul 444.6 394.3 high 113%

Notes

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 10 am on Thursday 1 September 2011. 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, as they cannot then be calculated reliably.
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.

Records in this summary are based on sites with at least 10 years of data.

*Official Perth observations have been recorded at several different sites with varying instrumentation over the years, and these changes can affect the continuity of the climate record. For the current Mt Lawley site, the most significant changes of this kind relate to minimum temperature and rain days.

For that reason, current mean temperature and rain-day data quoted here are based only on readings from the Mt Lawley site, which commenced observations in 1993. Sunshine recordings are from Perth Airport and for similar reasons current means use only Perth Airport data, which commenced in 1993.

For PDF files of Perth Metro climate statistics for other months, please click here for extremes and here for averages.

Further information

Media
(03) 9669 4057
Enquiries