Wednesday, 1 August 2012 - Monthly Climate Summary for Western Australia - Product code IDCKGC21R0
Record low rainfall was observed across a large part of southwest WA during July 2012 (see the maps below), particularly in western districts, centred on the Lower West. Many sites observed their driest July on record, including the centres of Perth, Northam, Goomalling, Narrogin, Wagin, and Collie; all of which have over 100 years of rainfall records (see the records tables below). Averaged across the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay), July 2012 was the driest July since comparable records commenced in 1900, with a total of 36 mm. The previous lowest July total rainfall for this region occurred in 1918 (47 mm), whilst the third lowest was 2005 (48 mm). The very low rainfall during July 2012 was the result of persistent high pressure systems over southern WA during the month and a contraction of the usual fronts and westerly winds southwards.
Below to very much below average rainfall was observed in much of the remainder of the Southwest Land Division (SWLD), apart from areas in the South and Southeast Coastal districts where rainfall was above to very much above average where an onshore flow for much of the month resulted in consistent showers. The SWLD recorded its second driest July, only behind the July of 2005.
Very low rainfall totals were observed across the state outside of the SLWD, however this is not uncommon for this time of year. The low rainfall throughout much of WA resulted in July 2012 ranking as the 3rd driest on record for WA behind 1937 and 1977.
Individual rainfall events over southern WA were mainly confined to cold fronts moving through the region on the 6th to 8th, 10th to 12th, 16th to 17th, and 23rd to 24th. Otherwise, strong ridging over southern WA resulted in generally clear conditions across much of the state for the month, aside from onshore showers along the south coast. A stronger cold front moved over the southwest corner early on the 31st, bringing widespread rainfall to the SWLD.
The very dry July in the Lower Southwest follows a near average June and the 7th driest autumn on record for the region. As a result, the Lower Southwest has seen its 6th driest January to July period, with the driest being 2001, the 3rd driest 2010, and the 5th driest 2006 (i.e. four of the driest such periods have occurred since 2001). The Lower Southwest has also experienced its 5th driest April to July, 4th driest May to July, and 8th driest Jun to July periods on record in 2012.
Above to very much above average maximum temperatures were observed over much of western WA, as well as in the southeast of the state during July. Most of western WA was up to 2 °C warmer than normal with patches of up to 3 °C warmer than normal in the west Gascoyne. The only area with below average mean monthly maxima was in the east Kimberley and adjacent northern Interior, where temperatures were up to 3 °C cooler than normal, while the remainder of the state was close to average.
When averaged across the state as a whole, the mean maximum temperature for WA during July 2012 was near average, whilst for the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay), daytime temperatures were very much above average and ranked as the 7th warmest July on record. This continues the very warm year to date in the Lower Southwest where alomst all months have seen above average maxima, aside from February. The mean maximum for the first seven months (January to July ) was 0.9 °C above normal and ranked as the 4th warmest January to July period since comparable temperature records commenced in 1950, largely due to a very warm autumn (5th warmest) and a very warm July (7th warmest). This "warm" run of temperatures has persisted for almost three years as the Lower West has only recorded two below average months, in terms of maximum temperature, since September 2009.
Warmer than normal daytime temperatures were observed through much of western and southern WA from the 1st to the 7th as a high moved through the Bight and directed warm northeasterly winds over the area. In contrast, the high directed cool southeasterly winds over the Kimberley resulting in relatively cool daytime temperatures during this period. A trough moved eastward through WA on the 10th and 11th, with warm conditions in the northerly flow ahead of the trough over central and eastern WA. Cooler southerly winds extended across southern WA as a ridge developed in the wake of the trough, with Norseman Aerodrome observing the coolest day in WA in July 2012 with a maximum of 10.1 °C on the 10th, and cooler than normal days extended through much of WA up to the 14th. Warm days were observed across the Pilbara and adjacent Kimberley on the 17th and 18th as a trough deepened over the Gascoyne. The warmth extended across western WA from the 19th to 22nd as the trough deepened along the west coast ahead of a cold front. Warm conditions returned to western WA on the 29th and 30th due to a high in the Bight directing northerly winds over the region.
Most of WA saw below to very much below average mean minimum temperatures during July 2012, with areas of lowest on record in the central eastern and southeastern Interior, and in central parts of the Lower West and neighbouring districts. Most of WA saw overnight temperatures at least 1 °C cooler than normal, with means up to 5 °C cooler than normal in the central eastern Interior. The only areas with close to average minima for July 2012 were parts of the south coast, far northern Gascoyne, west Pilbara, and small pockets of the Kimberley.
When averaged across the state as a whole, the July 2012 mean minimum temperature ranked as the coldest on record for WA. Comparable records commenced in 1950. The very cold July, combined with each month during 2012 recording overnight temperatures below the average (including the 4th coldest May), has resulted in WA observing its 3rd coolest January to July period on record. The Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) observed very much below average overnight temperatures during July 2012 but, in contrast to the WA average so far this year, it was only the second month to do so since October 2010.
The cool to cold overnight temperatures observed throughout much of WA during July 2012 were the result of persistent ridging across the south of the state resulting in generally clear skies and light winds, and an associated lack of rainfall, with numerous sub-zero minima observed at sites in central and southern WA throughout the month.
|Extremes in July 2012|
|Hottest day||35.1 °C at Wyndham Aero on the 13th|
|Warmest days on average||31.2 °C at Kalumburu|
|Coolest days on average||15.2 °C at Katanning|
|Coldest day||10.1 °C at Norseman Aero on the 10th|
|Coldest night|| -4.2 °C at Yeelirrie
on the 7th
-4.2 °C at Warburton Airfield on the 8th
|Coolest nights on average||0.8 °C at York|
|Warmest nights on average|| 21.1 °C at Troughton
17.9 °C at Truscott
|Warmest night|| 23.1 °C at Troughton
Island on the 28th
21.5 °C at Truscott on the 13th
|Wettest overall||141.4 mm at Walpole|
|Wettest day||39.0 mm at Warra Jarra on the 8th|
|Highest wind gust||87 km/h at Geraldton Airport on the 10th|
|Record lowest total July rainfall|
| Total rainfall
for July 2012 (mm)
| Previous driest
|Perth Metro*||34.6||61.5||in 1876||137||165.4|
|Doongin Peak||7.0||7.6||in 2005||118||53.3|
|Cape Naturaliste||49.8||67.6||in 2001||108||161.2|
|Berkshire Valley||13.0||16.8||in 1957||106||82.5|
|Rushy Pool||8.0||13.8||in 1957||101||67.6|
|Dalwallinu Comparison||14.7||17.4||in 1937||100||59.7|
|Forest Grove||88.0||90.3||in 1971||86||222.2|
|Margaret River||80.4||93.0||in 2001||84||215.7|
|Happy Valley||10.8||11.5||in 1937||76||58.4|
|Perth Airport||30.6||63.4||in 2005||69||157.3|
|Dandaragan West||32.4||42.2||in 1976||58||118.8|
|Pearce RAAF||23.2||54.4||in 1976||58||135.2|
|Chapman Hill||53.8||58.4||in 2001||54||171.2|
|Gosnells City||35.6||70.3||in 2005||51||162.0|
|Badgingarra Research Stn||24.0||25.8||in 1976||50||104.7|
|Albany Airport Comparison||55.0||56.6||in 1965||49||119.9|
|Avondale Farm||13.4||18.9||in 1976||48||70.1|
|Ferguson Valley||61.0||81.2||in 2001||40||174.6|
|Swan View||24.6||61.0||in 2005||39||159.8|
|Jandakot Aero||34.6||76.4||in 1976||38||174.5|
|Pickering Brook||28.7||94.6||in 1976||36||198.9|
|Gibb Rock||10.2||15.0||in 2005||31||45.0|
|Medina Research Centre||39.4||76.1||in 2005||30||147.9|
|Record highest July temperature|
in July 2012 (°C)
|Jurien Bay||26.2||on the 21st||= 26.2||on the 15th in 1977||43||19.4|
|Record highest July mean daily maximum temperature|
Mean daily maximum
for July 2012 (°C)
|Record lowest July temperature|
in July 2012 (°C)
|Beverley||-2.6||on the 19th||= -2.6||on the 20th in 1997||43||5.2|
|Jurien Bay||0.5||on the 25th||0.6||on the 26th in 1990||43||9.4|
|Record lowest July mean daily minimum temperature|
Mean daily minimum
for July 2012 (°C)
|Northam||1.9||= 1.9||in 1997||108||5.4|
|Giles Meteorological Office||3.1||3.7||in 1983||55||6.9|
|Ongerup||4.3||= 4.3||in 2010||44||5.8|
|Jurien Bay||6.1||7.0||in 2010||42||9.4|
|Warburton Airfield||2.0||3.0||in 1943||37||5.8|
|Summary statistics for July 2012|
|North Kimberley (district 01)|
|Troughton Island||27.6||-0.6||29.7||15th||21.1||-1.1||19.2||24th||0||2.8||v low||0%|
|Wyndham Aero||30.4||-1.4||35.1||13th||14.2||-1.0||9.6||3rd||0||3.1||v low||0%|
|East Kimberley (district 02)|
|Argyle Aerodrome||28.3||-1.4||33.9||11th||13.6||-2.1||9.5||4th||0||1.4||v low||0%|
|Halls Creek Airport||25.6||-1.6||31.3||11th||11.3||-1.3||7.1||7th||0||6.0||lowest||0%|
|West Kimberley (district 03)|
|Curtin Aero||29.9||-1.1||34.5||18th||13.3||-2.1||6.2||8th||0||7.9||v low||0%|
|Fitzroy Crossing Aero||29.3||-1.5||33.1||17th||9.8||-2.5||3.9||4th||0||6.7||v low||0%|
|West Roebuck||29.8||-1.2||34.4||18th||10.0||-2.6||4.2||3rd||0||19.6||v low||0%|
|De Grey (district 04)|
|Marble Bar||26.4||-0.9||30.8||18th||10.8||-1.4||5.4||9th||0||19.3||v low||0%|
|Port Hedland Airport||27.1||-0.1||30.9||25th||10.6||-1.7||5.8||9th||0||11.1||lowest||0%|
|Fortescue (district 05)|
|Barrow Island Airport||23.0||-0.8||27.2||24th||15.8||-1.9||11.8||15th||1.0||13.7||average||7%|
|West Gascoyne (district 06)|
|Emu Creek Station||26.6||+1.2||31.1||20th||10.3||-1.0||5.6||7th||1.6||21.8||average||7%|
|Shark Bay Airport||22.9||+0.2||27.3||30th||9.4||-1.2||4.7||4th||28.2||30.4||average||93%|
|East Gascoyne (district 07)|
|Murchison (district 07A)|
|Meekatharra Airport||20.1||+1.1||24.0||10th||6.5||-0.9||1.8||13th||0.8||21.6||v low||4%|
|Mount Magnet Aero||19.1||+0.5||24.2||31st||5.4||-1.6||2.1||13th||10.6||32.4||low||33%|
|North Coast (district 08)|
|Geraldton Airport Comparison||20.5||+1.0||24.9||21st||7.5||-1.9||1.6||25th||44.4||91.8||low||48%|
|Wongan Hills||18.0||+1.0||22.7||21st||5.1||-1.5||0.0||25th||14.6||69.4||v low||21%|
|Central Coast (district 09)|
|Badgingarra Research Stn||18.2||+0.6||23.4||21st||6.6||-0.7||1.8||25th||24.0||104.7||lowest||23%|
|Garden Island HSF||17.8||0.0||22.3||30th||9.9||-1.2||5.6||13th||40.6||114.4||v low||35%|
|Gingin Aero||18.9||+0.7||24.2||21st||3.6||-2.7||-2.7||25th||44.6||123.7||v low||36%|
|Jurien Bay||20.6||+1.2||26.2||21st||6.1||-3.3||0.5||25th||46.9||112.7||v low||42%|
|Medina Research Centre||19.4||+1.2||24.0||21st||5.4||-2.9||0.3||25th||39.4||147.9||lowest||27%|
|Rottnest Island||18.0||+0.3||22.1||30th||12.2||-0.1||9.1||18th||54.8||143.9||v low||38%|
|South Coast (district 09A)|
|Albany Airport Comparison||16.6||+0.8||20.1||21st||6.9||-0.6||2.8||5th||55.0||119.9||lowest||46%|
|Bridgetown Comparison||17.1||+1.3||21.9||30th||3.3||-1.1||-1.5||5th||48.2||146.1||v low||33%|
|Busselton Aero||16.8||+0.1||21.0||21st||5.5||-1.3||1.1||9th||49.6||128.9||v low||38%|
|Cape Leeuwin||17.7||+1.3||21.5||5th||12.0||+0.7||7.1||9th||70.4||181.5||v low||39%|
|Collie East||16.7||21.3||21st||1.9||-2.4||5th||39.2||122.2||v low||32%|
|Hopetoun North||18.1||0.0||23.5||31st||7.7||0.0||3.0||5th||129.8||69.8||v high||186%|
|Rocky Gully||15.3||+0.7||18.9||21st||6.3||-0.1||0.3||9th||53.4||96.0||v low||56%|
|North Central (district 10)|
|Cunderdin Airfield||18.0||+1.1||23.6||21st||1.9||-2.8||-2.9||19th||4.2||48.9||v low||9%|
|South Central (district 10A)|
|Katanning Comparison||16.0||+1.4||20.2||21st||24.1||75.2||v low||32%|
|Lake Grace||16.1||+0.5||20.3||6th||3.8||-1.5||-1.1||18th||18.0||38.0||v low||47%|
|Lake Grace Comparison||16.2||+0.8||20.4||22nd||4.0||-1.6||-0.8||18th||13.6||47.4||v low||29%|
|Newdegate Research Station||16.2||+1.1||20.3||21st||2.6||-1.5||-2.6||20th||6.4||47.6||v low||13%|
|Eucla (district 11)|
|Red Rocks Point||18.6||23.9||8th||6.6||2.6||7th||13.8|
|South East (district 12)|
|Munglinup West||16.6||0.0||22.1||6th||6.0||-0.7||2.9||19th||81.2||42.2||v high||192%|
|Salmon Gums Res.Stn.||17.0||+1.0||22.5||31st||2.9||-1.7||-2.8||21st||30.8||36.9||average||83%|
|Southern Cross Airfield||17.0||+0.5||21.8||31st||1.4||-2.1||-2.9||25th||13.0||34.6||v low||38%|
|North East (district 13)|
|Giles Meteorological Office||19.1||-0.9||24.7||11th||3.1||-3.8||0.3||3rd||0||11.7||lowest||0%|
|Offshore Islands (district 200)|
|Christmas Island Aero||26.3||+0.1||26.8||6th||22.7||+0.2||21.6||26th||12.6||94.8||low||13%|
|Cocos Island Airport||28.7||+0.7||29.7||4th||25.0||+1.0||21.2||14th||165.4||213.6||average||77%|
|Varanus Island||23.3||-1.0||26.1||25th||18.9||-1.0||17.0||6th||0||10.4||v low||0%|
A Monthly Climate Summary is prepared to list the main features of the weather in Western Australia 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 Wednesday 1 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
(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 30 years of data.