Tuesday, 1 May 2012 - Monthly Climate Summary for Western Australia - Product code IDCKGC11R0

Western Australia in April 2012: A warm dry month for southern WA

• Rainfall: below average for WA
• Maximum temperature: near average for WA; above average for southwest WA
• Minimum temperature: below average for WA; above average for southwest WA

Extremes Maps Records Summaries Important notes the top

Rainfall

Rainfall during April 2012 was below to very much below average in much of the southern half of WA, particularly in eastern parts of the Southwest Land Division (SWLD) and western parts of the Goldfields. Western parts of the SWLD including the Perth Metropolitan area saw heavy rainfall during the last few days of the month to record near average or above average April rainfall. In the north of the state, rainfall was mostly near average, with small areas of below average rainfall in the Gascoyne and west Pilbara. Rainfall in the Kimberley was a mixture of above and below average, with a generally quiet month to end the wet season apart from some heavy rainfall towards the end of the month in eastern parts. When averaged across the state, April 2012 rainfall was below average, whilst the Lower Southwest (southwest a line from Jurien Bay to Bremer Bay) and SWLD also experienced below average rainfall.

A westerly flow over the south of the state brought light to moderate showers during the first few days of April 2012 before a strong high moved into the Bight on the 6th. A stagnant trough over central parts of the state early in April caused showers and thunderstorms in central and northern parts, contracting to the Kimberley on the 10th and mostly clearing on the 11th. Generally dry conditions then persisted across much of WA, aside from a few isolated thunderstorms in central parts, before a series of weak fronts moved across southern WA from the 18th to 21st, causing generally light falls. Showers and thunderstorms returned to the Kimberley from the 20th to 25th, with heavy falls in eastern parts of the district on the 23rd and 24th. The heaviest daily totals in WA for April 2012 were observed during this period, with 104.2 mm at El Questro in the 24 hours to 9am on the 24th breaking the April record at the site of 89.6 mm set on 4 April 2011. Another strong high moved into the Bight on the 23rd, maintaining dry conditions over the south for the next few days, and clearing the storms in the Kimberley on the 26th. A low to the west of the state and a rainband brought moderate to heavy falls to the southwest of WA on the 28th and 29th, particularly in the Lower West and Southwest districts.

Rainfall in WA during the 2011/12 northern wet season (October-April) was generally above to very much above average, with small areas of highest on record in the southwest Kimberley and northeast Gascoyne. Sites in the southeast Central Wheat Belt and eastern Great Southern also saw their wettest October to April period, mainly due to a wet October and very heavy rainfall during early December. Dampier Downs in the west Kimberley observed its highest wet season rainfall total with 864.4 mm, breaking its previous record of 839.4 mm set in 1977/78. Two tropical cyclones crossed the Pilbara coast during the season, TC Heidi in early January and TC Lua in mid March, whilst TC Iggy also affected the WA mainland in late January and early February before crossing the Central West coast as a tropical low. A strong monsoon burst, associated with TC Iggy off the northwest coast, brought very heavy rainfall to the west Kimberley, with Cygnet Bay and Cape Leveque recording four consecutive days of over 100 mm, from 26 to 29 January. Such a sequence of four consecutive days over 100 mm had not been recorded before in WA. The highest daily rainfall total for the 2011/12 wet season in WA was 260.6 mm at Troughton Island in the north Kimberley, whilst Doongan observed the highest total for the wet season with 1798.2 mm, followed by Kalumburu with 1411.4 mm.

Maximum temperature

Much of southern and western WA, as well as the Interior, saw above to very much above average maximum temperatures in April 2012, with areas up to 3 °C warmer than normal in the eastern SWLD, southwest Gascoyne, Eucla, and southern Interior. Eyre in the Eucla observed its warmest April in 52 years of record with a mean maximum temperature of 26.6 °C which is 2.6 °C above the long-term mean. Below average maximum temperatures were confined to the east Kimberley and coastal parts of the east Pilbara and far west Kimberley, with an area of up to 2 °C below normal in the east Kimberley. When averaged across the state, the mean maximum temperature for WA during April 2012 was near average, whilst the mean maximum temperature over the Lower Southwest was above average.

Unseasonally hot conditions were observed in the Interior and adjacent Eucla to start the month, with Giles observing its equal hottest April day on record as it registered a maximum temperature of 38.3 °C on the 1st. The hot conditions persisted until the 6th when a high in the Bight brought a cooler southeasterly flow. Hot days were also observed in the southwest of the state from the 9th to 11th due to warm northeasterly winds. A ridge developed along the south coast on the 22nd in the wake of a cold front, resulting in the coldest day for the month in WA being recorded at Ravensthorpe in the Southeast Coastal district with a maximum of 14.4 °C. Relatively low temperatures were observed across much of the north of the state from the 24th through to the end of the month due to a strong high in the Bight directing a cool southeasterly flow over the area.

Minimum temperature

April 2012 saw much of WA experiencing near average mean minimum temperatures. Areas of below to very much below average minima were evident in much of the Kimberley, inland Pilbara, east Gascoyne and northern Goldfields, with an area of up to 3 °C cooler than normal minima in the northern Goldfields. Above average overnight temperatures were observed in western and southern parts of the SWLD, parts of the eastern Interior, eastern Eucla, and west Pilbara with up to 2 °C warmer than normal mean minimum temperatures along parts of the SWLD coast and up to 4 °C warmer than normal minima in the northeast Interior.

A stagnant airmass over the east of the state to begin the month resulted in warm nights in the Interior and adjacent east Eucla, before a strong high moved into the Bight and directed cool southeast winds over the area on the 7th. A strong high moved into the Bight in the wake of a cold front on the 23rd, resulting in cool nights across much of the south of the state, with the coldest night of the month in WA observed at Eyre on the 25th when the temperature dropped to -0.1 °C. The cool air pushed northwards over subsequent days, resulting in cool nights over the north of the state to end the month. Wyndham observed its coolest April night in 45 years of record with 15.7 °C on the 30th, beating the previous record of 15.9 °C set only last year, while several sites with shorter periods of record also observed their coolest April night on the 30th.

Extremes Maps Records Summaries Important notes the top

Maps
	Observed	Anomaly	Decile rank
Total rainfall
Mean daily maximum temperatures
Mean daily minimum temperatures

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Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top