Thursday, 31 May 2012 - Monthly Climate Summary for Perth - Product code IDCKGC11L0

Perth in May 2012: A dry month

• Rainfall: Below to very much below average at most sites
• Maximum temperature: Near average to above average at some sites
• Minimum temperature: Near average

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Rainfall

Rainfall totals in May 2012 were generally below to very much below average in the Perth metropolitan area; however, a few sites recorded close to average rainfall. Pearce RAAF, Mundaring and Perth Airport observed their driest May in over 10 years, with these sites recording less than 40% of their average rainfall for May.

A low and trough moved across the southwest of WA from 3 to 6 May 2012, bringing the first significant rainfall to the Perth area for the month, with a few moderate falls observed over the period. Generally light rainfall continued for the next few days, with a cold front crossing the metropolitan area on the 7th and a westerly flow maintaining showers through to the 10th. Further cold fronts crossed the southwest of the state, bringing light falls to the Perth area from the 13th to 17th, before a strong high moved into the Bight for much of the remainder of the month. A slow moving cold front moved over Perth on the last day of the month bringing some showers to break the two week dry spell.

Perth Metro recorded 49.0 mm of rainfall on 9 rain days in May 2012, well below the long term average of 117.3 mm on 11.3 rain days. Historically, May rainfall extremes have ranged from 14.1 mm in 1964 to 308.1 mm in 1879. Last May (2011), Perth Metro recorded 85.0 mm on 7 rain days. For the year to date (January to May), Perth Metro has recorded 160.8 mm of rainfall on 25 rain days. The average for the five months is 202.8 mm on 26.5 rain days, whilst last year (2011) Perth Metro recorded 135.0 mm on 21 rain days.

Maximum temperature

Mean maximum temperatures in May 2012 were generally close to average across the Perth metropolitan area and in the low twenties; though Pearce RAAF and Perth Airport recorded mean maxima for the month over 1 °C higher than normal.

Warm conditions in the mid-to-high twenties were experienced in the Perth region on 2 and 3 May 2012 in warm northerly winds as a trough approached from the west, with all sites in the region observing their warmest day for the month in this period, and Pearce RAAF recording the highest temperature for the month in the Perth metropolitan area with 28.2 °C. Cooler temperatures followed due to a westerly flow with most sites observing their coolest day on the 9th, including Bickley which observed the coolest day in the Perth area in May with a maximum of 16.5 °C. A return to warm northeast winds on the 11th and 12th saw maxima return to the mid-twenties. Frontal activity to the south saw cooler days from the 14th to 16th, before a high moved into the Bight and brought some warmer days from the 19th to 21st. A weak westerly flow saw cooler days on the 22nd and 23rd, before a strong high again moved into the Bight with temperatures remaining in the low-to-mid twenties for the remainder of the month.

Perth Metro's mean daily maximum temperature in May was 23.1 °C, which is close to the average of 22.4 °C. Daily maxima ranged from a mild 19.6 °C on the 9th to warm 27.3 °C on the 2nd. Despite a near average mean maximum temperature, Perth Metro observed 30 days of 20 °C or greater in May, breaking the record of 29 set in 2011. The lowest maximum temperature for May 2012 of 19.6 °C was the highest observed 'lowest maximum temperature' on record for May, breaking the record of 19.3 °C set in 1983 (daily temperature records commenced in 1897).

Perth Metro's mean daily maximum temperature for the year to date (January to May) period is 29.1 °C, which is the equal 3rd warmest (equal with 2009) since records commenced in 1897. The warmest year to date (January to May) was 29.8 °C, recorded last year (2011), whilst the long-term average for the five month period is 28.0 °C.

Minimum temperature

Mean minimum temperatures in May 2012 were generally close to average across the Perth metropolitan area.

May 2012 commenced with warmer than normal nights observed for much of the first half of the month, with the warmest night at all sites occurring between the 3rd and 5th, coinciding with the warmest daytime temperatures for the month. In contrast, cooler than normal temperatures were observed for much of the second half of the month, with several strong highs over the south of the state directing cool dry air over the region for much of the period. Very cold conditions were observed at most sites from the 23rd to 27th, with Jandakot and Gosnells City observing their coldest May night on record on the 25th, and Jandakot recording a minimum of -0.6 °C, the lowest temperature recorded in the Perth metropolitan area for May.

Perth Metro observed a minimum temperature of 1.3 °C on the 25th, which is the lowest May minimum temperature observed at the Mt Lawley site since records commenced in 1994, breaking the record of 2.4 °C on 27 May 2004. It was also the equal coldest May night observed at any of the past official Perth Metro sites (commencing in 1897), equal with the 1.3 °C observed on 11 May 1914.

Perth Metro's mean daily minimum temperature in May was 10.4 °C, which is close to the average of 10.7 °C. The warmest night during the month was 18.9°C on the 3rd.

Sunshine

Perth recorded an average daily sunshine of 7.5 hours in May, which was the sunniest May since the 8.1 hours in 2009 (the sunniest May on record). The average sunshine hours for May is 6.9 hours per day.

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* note: there are gaps in the historical record at this site, so it is possible a lower value has gone unreported.

Extremes Records Summaries Important notes the top

Extremes Records Summaries Important notes the top

Extremes Records Summaries Important notes the top

Extremes Records Summaries Important notes the top

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.

Extremes Records Summaries Important notes the top