Perth in July 2012: Driest July on record

  • Rainfall: driest July on record for most sites
  • Maximum temperature: above average for most sites, with record highs at some sites
  • Minimum temperature: very much below average for most sites, with record lows at some sites

Rainfall

Due to persistent high pressure systems over southern WA and a contraction of cold fronts and westerly flow southwards during the month, July rainfall totals across the Perth metropolitan area were lowest on record at almost all sites (see the records tables). Rainfall totals in the region were in the 20 to 50 mm range, more than 100 mm less than the long-term average at most sites, and significantly below the previous July record. This event was particularly notable given that some sites have over 100 years of record (Perth Metro 136 years, Jarrahdale 128 years, and Mundaring 111 years), and the low monthly rainfall easily exceeded their previous lowest July total.

July 2012 saw only a handful of light rainfall events in the Perth area, with daily rainfall totals generally less than 10 mm. A slow moving cold front and pre-frontal trough brought generally light rainfall to the Perth area on the 6th and 7th, followed by further mainly light rainfall from a low and associated middle level disturbance on the 10th. A westerly flow and the passage of weak cold fronts brought light rainfall on the 16th, while a weak front brushed southwest WA with the Perth area only recording light rainfall on the 23rd, with a daily falls less than 5 mm for most of sites. A cold front and pre-frontal trough moved over southwest WA during the early morning of the 31st, bringing welcome moderate rainfall to the metropolitan area, though totals in the 24 hours to 9am on the 31st were below 13 mm.

Perth Metro recorded 34.6 mm of rainfall on 8 rain days in July 2012, easily breaking the previous lowest July total of 61.5 mm on 9 rain days in 1876. As a result of the extraordinarily dry July, and a near average June, Perth Metro recorded its 3rd driest June to July period with 175.4 mm on 26 rain days. It was also the 4th driest January to July period on record at Perth Metro with 336.2 mm on 51 rain days, mainly due to a below average May and the record low July.

Maximum temperature

Mean maximum temperatures in July 2012 were above average for most sites in the Perth metropolitan area and mostly between 18 °C and 20 °C. Swanbourne on the coast recorded their warmest July in 18 years of record, whilst Bickley in the hills saw its equal warmest July in 18 years of record, equal with 1999. Medina in the southern suburbs also experienced its equal warmest July in 25 years of record, equal with 2007.

Warm conditions were observed across Perth in the first week of July 2012 due to a strong high to the south of the state directing warm northerly winds over the region. Maximum temperatures were regularly above 20 °C for the first six days at most sites and Perth Metro recorded its warmest start to July since records began in 1897 with a mean maximum of 21.6 °C in the first seven days. Maximum temperatures dropped to below normal between the 8th and 12th, and again on the 17th and 18th as cold fronts and a westerly flow affected the region. Warm weather returned between the 20th and 23rd due to a strong high pressure cell in the Bight, before a westerly flow resulted in a dip in temperatures on the 24th and 25th, with a number of sites registering their coldest day of the month on the 24th. Warm conditions returned towards the end of the month as a high re-established itself in the Bight, with most sites observing their warmest day for July 2012 on the 30th. The daily maximum temperature of 24.4 °C at Swanbourne on the 30th was the highest temperature of the month in the Perth metropolitan area.

Perth Metro's mean daily maximum temperature in July was 19.4 °C, which was its warmest July for five years since a mean of 19.5 °C was recorded in 2007. Daily maxima ranged from a cold 14.8 °C on the 24th to a warm 23.8 °C on the 30th, whilst the average maximum for July at Perth Metro is 18.3 °C.

Minimum temperature

Mean minimum temperatures in July 2012 were below to very much below average for most sites in the Perth metropolitan area, with mean minima mostly in the 5 °C to 8 °C range and 2 to 3 °C cooler than normal, with only Rottnest Island above 10 °C. Perth Metro, Medina Research Centre, Jandakot Aerodrome, and Garden Island all registered their lowest mean minimum temperature for July on record.

Cool to cold nights were observed for most of July 2012, with generally clear skies throughout much of the month. The coldest night at most sites occurred on the 25th when Perth Airport, Pearce RAAF, and Jandakot Aerodrome registered sub-zero overnight temperatures. Jandakot Aerodrome also observed sub-zero temperatures on the 5th and 26th. Only a handful of nights scattered throughout July 2012 saw overnight temperatures above normal, generally coincident with cloudy conditions before a cold front moved through the metropolitan area.

Perth Metro's mean daily minimum temperature in July was 5.2 °C, which is the lowest mean minimum for any month at the current Mt Lawley site since records commenced in November 1993. Perth Metro recorded a total of 19 cold nights (a cold night at Perth Metro is a minimum of less than 5 °C), which is the greatest number recorded for any month at Perth Metro. The previous record was 16 cold nights in July 1998, 2001, and 2010. Perth Metro minima ranged from a cold 0.4 °C on the 25th to a mild 12.4 °C on the 22nd.

Sunshine

Perth recorded an average daily sunshine of 7.4 hours in July 2012, which was the second sunniest July on record, behind the 7.5 hours in July 1918. The average sunshine for July is 6.0 hours per day.

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Extremes in July 2012
Hottest day 24.4 °C at Swanbourne on the 30th
Warmest days on average 19.5 °C at Gosnells City
Coolest days on average 15.9 °C at Bickley
Coldest day 11.9 °C at Bickley on the 9th
Coldest night -1.6 °C at Jandakot Aero on the 25th
Coolest nights on average 3.8 °C at Jandakot Aero
Warmest nights on average 12.2 °C at Rottnest Island
7.8 °C at Swanbourne
Warmest night 15.8 °C at Rottnest Island on the 6th
14.8 °C at Pearce RAAF on the 22nd
Wettest overall 54.8 mm at Rottnest Island
47.8 mm at Jarrahdale
Wettest day 12.6 mm at Rottnest Island on the 17th
12.4 mm at Roleystone on the 31st
Highest wind gust 78 km/h at Rottnest Island on the 23rd

Record lowest total July rainfall
Total rainfall
for July 2012 (mm)
Previous driest
for July
Years of
record
Average for
July
Perth Metro* 34.6 61.5 in1876 136 165.4
Jarrahdale 47.8 72.7 in 1959 128 227.1
Mundaring 43.8 58.7 in 1889 111 214.5
Perth Airport 30.6 63.4 in 2005 69 157.3
Pearce RAAF 23.2 54.4 in 1976 58 135.2
Gosnells City 35.6 70.3 in 2005 51 161.6
Bickley 31.6 97.4 in 1976 44 217.5
Jandakot Aero 34.6 76.4 in 1976 38 174.5
Medina Research Centre 28.9 76.1 in 2005 30 147.6
Swanbourne 42.0 54.8 in 2005 19 145.8
Garden Island HSF 40.6 55.2 in 2005 11 114.4




Record highest July mean daily maximum temperature
Mean daily maximum
temperature
for July 2012 (°C)
Previous warmest
for July
Years of
record
Average for
July
Medina Research Centre 19.4 = 19.4 in 2007 25 18.2
Bickley 15.9 = 15.9 in 1999 18 15.0
Swanbourne 19.5 19.4 in 2007 18 18.3



Record lowest July mean daily minimum temperature
Mean daily minimum
temperature
for July 2012 (°C)
Previous coolest
for July
Years of
record
Average for
July
Medina Research Centre 5.4 6.0 in 2001 25 8.3
Jandakot Aero 3.8 4.1 in 2001 22 6.8
Perth Metro* 5.2 5.3 in 1997 19 7.9
Garden Island HSF 9.9 10.1 in 2010 10 11.1


Summary statistics for July 2012
Maximum temperatures
for July
(°C)
Minimum temperatures
for July
(°C)
Rainfall
for July
(millimetres)
Mean for
July
2012
Diff
from
average
Highest for
July
2012
Mean for
July
2012
Diff
from
average
Lowest for
July
2012
Total for
July
2012
Average
for
July
Rank of
July
2012
Fraction of
July
average
Bickley 15.9 +0.9 20.2 21st 6.3 -0.8 2.9 9th 31.6 217.5 lowest 15%
Champion Lakes 18.5   22.9 21st 7.6   2.7 25th 30.2
Garden Island HSF 17.8 0.0 22.3 30th 9.9 -1.2 5.6 13th 40.6 114.4 lowest 35%
Gosnells City 19.5 +0.9 24.2 30th         35.6 161.6 lowest 22%
Jandakot Aero 18.9 +1.1 23.7 30th 3.8 -3.0 -1.6 25th 34.6 174.5 lowest 20%
Medina Research Centre 19.4 +1.2 24.0 21st 5.4 -2.9 0.3 25th 28.9 147.6 lowest 20%
Pearce RAAF 18.8 +1.0 23.1 30th 5.6 -2.9 -0.8 25th 23.2 135.2 lowest 17%
Perth Airport 19.2 +1.3 23.8 21st 5.6 -2.4 -0.7 25th 30.6 157.3 lowest 19%
Perth Metro 19.4 +1.1 23.8 30th 5.2 -2.5 0.4 25th 34.6 165.4 lowest 21%
Rottnest Island 18.1 +0.4 22.1 30th 12.2 -0.1 9.1 18th 54.8 143.9 v low 38%
Swanbourne 19.5 +1.2 24.4 30th 7.8 -1.9 3.9 25th 42.0 145.8 lowest 29%

Daily maximum temperature
Central Coast (09) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Bickley 17.8 17.6 17.1 18.1 19.2 19.0 16.7 12.9 11.9 13.3 13.8 12.9 14.8 15.5 16.1 13.6 13.2 13.7 15.5 18.4 20.2 19.5 17.0 12.0 13.0 15.9 16.2 17.1 17.0 19.8 14.6
Champion Lakes 20.8 20.9 19.5 20.7 21.7 20.5 18.9 15.2 14.2 15.7 16.5 14.3 16.7 17.6 19.1 16.6 15.7 16.1 18.5 22.2 22.9 22.6 19.8 14.0 14.7 18.5 19.6 19.8 19.6 22.2 18.3
Garden Island HSF 19.2 20.0 19.5 20.8 21.3 21.3 16.9 15.5 15.4 15.9 15.7 14.5 16.1 17.4 19.4 16.8 14.9 14.0 16.7 19.0 18.1 20.7 18.8 13.8 14.9 16.4 16.7 20.3 19.6 22.3 20.2
Gosnells City 21.6 21.8 21.4 22.7 23.0 20.5 15.8 14.9 17.7 17.3 15.7 17.5 19.0 20.2 17.4 16.8 17.4 19.4 22.3 24.2 23.9 20.9 15.0 15.5 19.1 19.5 21.5 21.2 24.2 18.8
Jandakot Aero 20.6 20.7 20.2 21.5 22.8 21.5 19.2 15.7 14.8 16.7 17.1 15.0 17.6 18.3 19.9 17.3 15.9 16.0 21.4 23.5 22.0 20.2 14.6 15.1 18.7 18.5 20.5 20.2 23.7 18.9
Medina Research Centre 21.1 21.6 20.6 22.3 23.2 22.7 19.1 16.0 15.4 17.5 17.0 15.1 17.5 19.5 20.5 18.0 16.4 16.4 18.5 21.5 24.0 22.7 21.4 14.7 15.3 19.0 19.5 21.0 20.4 23.8 19.1
Pearce RAAF 20.2 19.6 20.0 20.9 21.8 21.9 19.0 15.2 14.7 15.6 16.7 17.6 18.2 19.1 16.7 16.3 16.0 18.0 21.9 22.2 21.9 19.8 15.1 15.8 18.4 18.6 19.4 20.5 23.1 20.2
Perth Airport 21.0 21.0 20.1 21.6 22.9 22.5 20.1 15.8 14.7 16.3 17.4 16.0 17.9 18.3 19.4 16.5 16.6 16.9 18.6 21.3 23.8 22.9 20.1 15.4 16.1 19.2 19.3 20.2 20.2 23.3 18.6
Perth Metro 21.6 21.0 20.5 22.2 22.8 22.6 20.3 16.0 15.0 15.7 17.3 15.7 17.7 18.8 20.2 17.3 16.6 16.5 18.7 21.8 23.6 23.4 20.5 14.8 15.9 19.3 19.3 20.7 20.8 23.8 19.5
Rottnest Island 19.9 20.3 20.3 21.0 21.4 20.7 17.8 14.5 14.4 15.2 15.7 14.6 16.8 17.8 19.9 16.7 14.9 14.6 17.4 19.8 20.1 21.3 20.1 13.1 15.8 17.5 17.7 19.5 19.4 22.1 19.6
Swanbourne 20.5 21.4 21.0 22.6 22.6 22.4 19.0 16.4 15.0 17.4 17.9 16.0 17.8 18.6 20.5 18.8 17.3 16.7 18.5 21.7 24.1 22.7 20.0 15.8 16.0 18.6 18.6 21.6 21.1 24.4 19.5

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.
The temperatures in this table are coloured by
their difference from the long-term average for the period
-10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 +1.0 +2.0 +3.0 +4.0 +5.0 +6.0 +7.0 +8.0 +9.0 +10.0 °C difference from average


Daily minimum temperature
Central Coast (09)12345678910111213141516171819202122232425262728293031
Bickley7.47.15.64.25.39.811.45.62.95.56.34.26.85.78.59.96.13.33.25.35.49.810.03.33.75.64.44.65.27.611.5
Champion Lakes7.68.38.38.08.37.811.67.96.28.46.25.75.05.38.212.06.47.14.06.09.211.88.04.72.74.47.07.67.912.612.2
Garden Island HSF9.99.810.211.511.113.112.39.87.49.411.08.75.68.612.115.111.26.96.27.18.913.29.68.37.56.38.49.010.712.614.8
Gosnells City5.06.58.27.57.111.07.54.43.56.88.07.64.51.63.55.07.08.010.112.3
Jandakot Aero3.52.62.80.6-0.22.79.46.13.69.14.10.51.30.97.69.65.51.50.20.03.511.14.90.8-1.6-0.41.12.32.810.412.2
Medina Research Centre5.05.53.97.26.56.910.96.32.08.86.42.32.52.28.010.07.43.01.72.43.511.36.02.60.31.02.45.45.78.912.8
Pearce RAAF5.15.25.85.06.32.69.17.14.49.27.43.62.30.89.29.43.74.10.94.05.914.89.73.1-0.80.02.23.16.411.712.5
Perth Airport4.35.48.27.87.55.010.36.83.37.77.42.82.72.58.69.63.93.20.53.04.712.16.14.4-0.70.54.73.37.010.211.5
Perth Metro4.74.33.22.52.64.910.97.84.38.27.03.73.23.18.810.85.02.21.21.84.312.46.95.00.41.62.53.13.77.712.2
Rottnest Island13.612.913.613.414.715.815.310.89.310.311.510.611.810.813.414.711.09.110.612.211.914.214.89.39.210.411.511.012.513.115.5
Swanbourne7.67.97.88.08.19.212.37.64.78.67.45.46.46.69.513.78.44.94.56.27.212.99.55.43.95.95.66.17.011.412.9

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.
The temperatures in this table are coloured by
their difference from the long-term average for the period
-10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 +1.0 +2.0 +3.0 +4.0 +5.0 +6.0 +7.0 +8.0 +9.0 +10.0 °C difference from average


Daily rainfall
Central Coast (09)12345678910111213141516171819202122232425262728293031
Bickley 0.2 - - - - - 4.4 0.4 - 5.6 1.4 - 0.2 0.2 - 2.0 5.8 0.2 - - - - - 1.0 - 0.2 - - - - 10.0
Champion Lakes 0.2 - - - - - 5.2 0.4 - 5.2 1.2 - - - 0.8 1.2 5.4 - 0.2 - - - - 0.8 - - - - - - 9.6
Garden Island HSF 0.2 0.2 - - - - 4.2 0.6 - 6.4 8.0 - - - 0.6 3.4 2.0 - - - 0.2 - - 1.8 - 0.4 - - - - 12.6
Gosnells City - - - - - »» 5.2 0.4 - 5.8 2.1 - - - - 2.1 5.2 0.1 - - - - - 6.0 1.0 - - - - - 7.7
Jandakot Aero - - - - - - 7.8 0.6 - 6.0 2.2 - 0.2 - - 1.4 8.4 - -
- - - 1.2 - - - - - - 6.8
Jarrahdale 0.2 - 0.2 0.4 0.2 - 7.8 1.0 - 5.0 5.8 0.4 0.2 0.2 0.8 4.4 4.6 - 0.4 0.2 0.2 - - 7.2 0.2 0.2 0.2 0.2 - - 7.8
Medina Research Centre - - - - - - 3.4 0.7 - 5.6 8.0 - - - 0.2 7.6 1.8 - - - - - - 1.6 - - - - - - 10.5
Mundaring 0.2 0.2



7.4 1.2
8.4 5.0 0.2
0.2 0.2 4.0 8.4 0.2 0.2 0.2 0.2 0.2 0.2 2.0 0.2 0.2 0.2 0.2

4.4
Pearce RAAF - -
- - - 4.2 0.8 - 5.2 4.8

- - 3.0 3.6

-

1.4 - 0.2 - - - - - -
Perth Airport - - - - - - 7.0 - - 6.6 3.8 - - - - 0.6 6.8 - 0.2 - - - - - 0.2 - - - - - 5.4
Perth Metro - - - - - - 9.0 0.2 - 6.4 3.2 - - - - 3.6 5.0 - - - - - - 0.4 - - - - - - 6.8
Roleystone





5.6















2.4





12.4
Rottnest Island - - - - - - 6.0 3.0 - 5.2 10.8 - - - 0.2 0.4 12.6 - - - - - 0.4 6.4 - - - - - - 9.8
Serpentine - - - - - - 8.8 0.6 0.2 5.6 8.4 - - - 0.6 2.4 3.6 - - - - - - 4.4 - - - - - - 10.4
Swanbourne - - - - - - 12.0 0.4 - 6.8 3.2 - 0.2 0.2 0.2 1.0 5.0 - - - - - 0.4 1.6 - 0.2 0.2 - - - 10.6

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

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

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 10 am on Tuesday 31 July 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.

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