Perth in July 2010: A month of cold nights

  • Near average to below average rainfall across the Perth area.
  • Near average mean maximum temperature.
  • Below average mean minimum temperature.

Rainfall

Rainfall around the Perth area in July 2010 was near average to below average, with totals ranging from about 80-90 mm at Rottnest Island and Garden Island to around 180 mm in the hills.

A strong cold front crossed the Perth area overnight on the 8th and brought moderate to heavy rainfall, with daily totals generally ranging from 30 mm to 50 mm. A vigourous southwesterly airstream and another cold front brought more rainfall over the next few days. Later in the month, a slow moving low to the south of WA followed by a cold front brought further rainfall from the 26th.

Perth Metro recorded 142.0 mm of rainfall on 15 rain days in July, which was the driest July since the 81.0 mm in 2006. Historically, July rainfall in Perth has ranged from 61.5 mm in 1876 to 425.1 mm in 1958 and the July average is 169.9 mm on about 17 rain days. Last July, Perth Metro registered 149.6 mm of rainfall on 16 days.

The total rainfall for the seven months from January to July 2010 at Perth Metro was 347.6 mm recorded on 38 rain days, which was the driest January to July period since the 215.6 mm in 2006 and the sixth driest since records commenced in 1876. The average for this period is 550.2 mm on about 60 days while the total for the same period last year was 371.0 mm on 51 days. Perth Metro has also seen the fourth driest start to winter on record, primarily due to a very dry (second driest) June.

Maximum temperature

Mean maximum temperatures in the Perth area during July 2010 were close to average, ranging from 15.0 °C at Bickley to 18.5 °C at Gosnells City.

The coldest day for the month was on the 9th with Jandakot Aero, Gosnells City and Bickley all breaking their coldest July daily maximum records. Bickley was the coldest, reporting a chilly 9.8 °C. The 25th was the warmest day of the month with daily maxima ranging from about 20 to 23 °C.

Perth Metro's mean maximum temperature in July was 18.2 °C, which is close to the average of 18.3 °C. Daily maxima ranged from a warm 22.7 °C on the 25th to a cold 13.3 °C on the 9th, which was also Perth Metro's coldest July day for seven years. Perth Metro's coldest day in July on record was 10.5 °C on 9 July 1906.

Minimum temperature

Mean minimum temperatures were below to very much below average for much of the Perth area with overnight temperatures generally 2 to 3 °C cooler than normal. Pearce RAAF and Gosnells City observed their lowest July mean daily minimum temperature; while cold nights on the 3rd and 4th saw Perth Airport and Pearce RAAF experience their coldest July night on record.

For the first 8 nights of July, many mainland sites saw a run of consecutive cold nights continuing from the last week of June (a cold night is a night with minimum temperature below 5 °C). Perth Airport's 15 consecutive cold nights from 24 June to 8 July is the longest run of cold nights in its 66 years of record (the previous record was 11 cold nights between 24 June and 4 July 1990).

Perth Metro's mean minimum temperature in July was 5.9 °C, equalling the second lowest on record also observed in 1998. Perth Metro's lowest mean daily minimum temperature in July was 5.3 °C in 1997 while the average is 7.9 °C. Daily minima in July 2010 ranged from the mild 12.6 °C on the 29th to a cold 0.0 °C on the 3rd, which equalled the record for the coldest July night set on 15 July 1997 and 27 July 1998.

During July 2010, Perth Metro recorded 16 cold nights, which equals the record for the greatest number of cold nights in July set in 1998 and 2001.

Wind & sunshine

Severe wind gusts were recorded at Rottnest Island on the 11th (104 km/h) as a strong cold front crossed the Perth area.

Perth recorded an average daily sunshine of 7.1 hours, which is the equal third highest on record with 2004. The long-term average is 6.0 hours whilst the sunniest July on record was 7.5 hours in 1918.

Further information

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Extremes in July 2010
Hottest day 23.6 °C at Gosnells City on the 25th
Warmest days on average 18.5 °C at Gosnells City
Coolest days on average 15.0 °C at Bickley
Coldest day 9.8 °C at Bickley on the 9th
Coldest night -1.9 °C at Jandakot Aero on the 3rd
-1.9 °C at Pearce RAAF on the 4th
-1.9 °C at Jandakot Aero on the 7th
Coolest nights on average 4.3 °C at Jandakot Aero
Warmest nights on average 11.7 °C at Rottnest Island
Warmest night 14.8 °C at Garden Island HSF on the 29th
Wettest overall 176.4 mm at Mundaring
Wettest day 55.0 mm at Bickley on the 9th
Highest wind gust 104 km/h at Rottnest Island on the 11th


Record lowest July daily maximum temperature
Lowest daily maximum
temperature
in July 2010 (°C)
Previous lowest
for July
Years of
record
Average for
July
Jandakot Aero 11.8 on the 9th 12.1 on the 14th in 2003 21 17.8
Gosnells City 12.0 on the 9th 12.5 on the 14th in 2003 19 18.6
Bickley 9.8 on the 9th 10.0 on the 14th in 2003 17 15.0



Record lowest July temperature
Lowest temperature
in July 2010 (°C)
Previous lowest
for July
Years of
record
Average for
July
Perth Airport -1.0 on the 3rd -0.8 on the 22nd in 2006 67 8.1
Pearce RAAF -1.9 on the 4th -1.0 on the 22nd in 2006 53 8.5



Record lowest July mean daily minimum temperature
Mean daily minimum
temperature
for July 2010 (°C)
Previous lowest
for July
Years of
record
Average for
July
Pearce RAAF 5.5 6.5 in 1997 49 8.5
Gosnells City 6.6 6.8 in 1997 18 8.9


Summary statistics for July 2010
Maximum temperatures
for July
(°C)
Minimum temperatures
for July
(°C)
Rainfall
for July
(millimetres)
Mean for
July
2010
Diff
from
average
Highest for
July
2010
Mean for
July
2010
Diff
from
average
Lowest for
July
2010
Total for
July
2010
Average
for
July
Rank of
July
2010
Fraction of
July
average
Bickley 15.0 0.0 19.8 25th 6.7 -0.4 3.0 3rd 175.6 220.7 low 80%
Champion Lakes 17.4   21.8 25th 7.7   2.7 4th 111.6
Garden Island HSF 17.4   19.8 25th 10.1   6.2 5th 84.2
Gosnells City 18.5 -0.1 23.6 25th 6.6 -2.3 1.1 4th 140.7 165.1 low 85%
Jandakot Aero 18.1 +0.3 22.3 25th 4.3 -2.6 -1.9 3rd 106.8 178.2 low 60%
Medina Research Centre 18.4 +0.2 22.0 25th 6.4 -2.0 0.2 3rd 123.0 151.2 average 81%
Pearce RAAF 17.9 +0.1 22.5 25th 5.5 -3.0 -1.9 4th 112.4 137.3 low 82%
Perth Airport 18.4 +0.5 23.1 25th 5.8 -2.3 -1.0 3rd 133.2 158.9 low 84%
Perth Metro* 18.2 -0.1 22.7 25th 5.9 -2.1 0.0 3rd 142.0 170.0 average 83%
Rottnest Island 17.3 -0.4 19.7 25th 11.7 -0.6 7.9 10th 88.2 113.4 average 78%
Swanbourne 18.2 -0.1 21.0 25th 8.3 -1.4 4.0 5th 148.0 151.3 average 98%

Daily rainfall
Central Coast (09)12345678910111213141516171819202122232425262728293031
Bickley - - - - - - - - 55.0 21.0 11.4 39.0 18.8 0.2 0.2 - 2.2 - - 0.2 - - - - - 4.6 1.2 5.2 16.2 - 0.4
Champion Lakes - - - - 0.2 - - - 41.6 13.6 8.0 21.2 6.0 - 0.2 - 3.0 - - - - - - - - 5.4 1.6 0.6 7.2 - 3.0
Garden Island HSF - 2.4 0.2 - - - - - 9.0 16.0 8.2 13.4 4.0 - 0.2 0.4 4.0 - 0.2 - - - - - - 2.4 5.2 3.0 8.6 1.2 5.8
Gosnells City »» 0.4 - - - - - - 48.4 22.0 14.6 22.3 7.4 0.2 - - 3.3 0.1 - - - - - - - 5.2 3.4 1.6 9.4 1.2 1.2
Jandakot Aero - 0.4 0.2 - - - - - 32.0 18.8 6.6 17.4 4.4 1.0 - - 3.0 - - - - - - - - 6.0 4.2 2.0 8.2 - 2.6
Jarrahdale - 0.6 - 0.2 0.4 - - 0.2 42.0 17.8 9.8 39.6 7.4 0.2 0.2 0.4 6.0 - 0.2 0.4 - 0.2 0.4 0.2 - 7.2 6.4 6.4 18.0 1.0 1.4
Medina Research Centre - 3.6 - - - - - - 35.4 14.2 13.0 19.6 4.6 0.2 - 1.6 1.0 - - - - - - - - 3.4 11.2 2.0 10.4 0.4 2.4
Mundaring 0.2 0.2 0.2 0.2 0.2 0.2 0.2
40.2 23.0 13.2 41.2 12.0 0.4 0.2 0.2 5.0 0.4 0.2 0.2 0.2 0.2 0.2 0.2
2.8 4.0 12.4 15.6 0.8 2.4
Pearce RAAF - - - - - - - - 29.4 20.0 13.6 24.2 5.8 - - - 3.4 - - - - - - - - - 3.0 3.0 8.4 0.8 0.8
Perth Airport - - - - - - - - 38.0 18.8 11.2 25.0 5.8 - - - 4.4 - - - - - - - - 5.2 4.0 2.0 17.0 0.2 1.6
Perth Metro* - 0.2 - - - - - - 40.6 17.6 12.8 21.8 6.2 0.2 0.2 - 9.0 - - - - - - - - 11.0 6.8 2.6 10.4 0.2 2.4
Rottnest Island - 6.0 - - - - - - 13.8 17.0 8.2 6.8 3.6 7.6 - - 6.6 1.8 5.0 - - - - - - 3.0 0.4 1.0 6.4 0.2 0.8
Serpentine





















-







Swanbourne - 3.0 - - - - - - 33.8 15.8 11.2 18.6 6.8 0.6 - - 5.8 - - - - - - - - 18.6 3.8 2.0 20.2 3.4 4.4

Most values are the precipitation in the 24 hours to 9 am on the day indicated. Days marked with »» are part of a longer accumulation, which is marked like this on the final day. Values over 100 mm have been rounded to the nearest whole millimetre. Days marked with - have a rainfall report of zero; days left blank have no rainfall report (which often indicates no rain fell).
This table is very wide; you may have to scroll sideways to see all the days, and you may need to set the paper to 'landscape' to print.


Notes

A Monthly 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 12 pm on Monday 2 August 2010. 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.

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 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