Perth in December 2011: A very wet December

  • Rainfall: Wettest on record for several sites, 3rd wettest for Perth Metro
  • Maximum temperature: Average to above average
  • Minimum temperature: Average to above average; highest on record for a number of sites

Rainfall

Rainfall across the Perth metropolitan area during December 2011 was well above average, with many sites experiencing their wettest December on record. Rainfall totals were generally in the 40 to 70 mm range, mainly as a result of two significant rainfall events in the first half of the month, which caused record December daily falls at several sites.

A deep middle level trough off the west coast produced significant rainfall and thunderstorms across the Perth metropolitan area on the 6th, and showers continued in the southeastern suburbs on the 7th. Rainfall totals during the event were generally in the 20 mm to 40 mm range, though heavier falls were recorded at Roleystone and Pearce RAAF. The daily rainfall total of 48.8 mm recorded at Pearce RAAF in the 24 hours to 9am on the 7th was its wettest December day in 48 years of record, as well as the wettest day of December 2011 in the Perth area.

Another deep mid-level trough off the WA west coast on the 12th brought heavy rain and thunderstorms across the Perth metropolitan area in the evening and early on the 13th, with several sites, including Perth Airport, experiencing their wettest December day on record. Most of the rain fell due to a slow moving storm in the hours just prior to midnight on the 12th, with Perth Metro recording 36.6 mm in 30 minutes (between 2202 WST and 2231 WST), which is a one in 50 to a one in 100 year event. The daily total of 43.6 mm at Perth Metro on the 13th was its third wettest December day since records commenced in 1876.

Perth Metro observed 75.8 mm on 3 rain days in December 2011, which was the third wettest December on record, and the wettest since 80.7 mm was recorded on 11 rain days in 1951. Last December, Perth Metro recorded 11.6 mm on 6 rain days.

Maximum temperature

Mean maximum temperatures were above average for most sites in the Perth metropolitan area, with temperatures mostly between 1.2 °C and 2.4 °C above average, though mean maxima at Pearce RAAF, Gosnells, and Bickley were close to average. Mean maximum temperatures were generally in the 28 °C to 31 °C range.

Several coastal plain sites experienced a heatwave (three or more consecutive days with maximum temperatures of 35 °C or higher) between the 3rd and 5th with temperatures in the 35 °C to 37 °C range, as a high pressure system moved slowly south of the state into the Bight directing dry and hot northeasterly winds over the Perth region. The temperature dipped sharply on the 6th due to a cool southerly change, with maximum temperatures in the low twenties and all sites observed their coolest day of the month. Bickley observed the coolest day across the Perth region with a maximum temperature of only 20.3 °C. Maximum temperatures warmed up towards the end of the month, with the hottest day on the 28th when daily maxima for all sites climbed above 36.0 °C. The 40.1 °C on the 28th at Swanbourne was the highest temperature recorded in the Perth metropolitan area for the month.

Perth Metro's mean daily maximum temperature in December 2011 was 30.5 °C, which was above the average of 28.8 °C for December. Daily maxima in December 2011 ranged from a mild 23.9 °C on the 13th, to a very hot 39.9 °C on the 28th. The first five days of December saw temperatures between 32 °C and 38 °C at Perth Metro, with a mean over this period of 35.4 °C. This was the warmest start to December at Perth Metro since records commenced in 1897, exceeding the previous warmest start to the month with a mean of 35.0 °C from 1 to 5 December 1967.

Minimum temperature

Mean minimum temperatures in December 2011 were very much above average across the Perth area, with a number of sites observing their warmest December on record due to consistently above average nights and some very warm nights in the early and latter parts of December. Mean overnight temperatures were generally in the 17 °C to 19 °C range.

Warm nights (when the daily minimum temperature is 20 °C or higher) were experienced at many sites between the 4th and 5th, and on the last four days of the month. The daily minimum temperature of 25.9 °C at Gosnells City on the 29th was the highest overnight temperature of the month in the Perth area.

Perth Metro's mean daily minimum temperature in December 2011 was 18.2 °C, which is 2.0 °C above the average and the warmest December for 32 years since a mean minimum of 18.5 °C was recorded in 1979. Daily minima ranged from a mild 13.3 °C on the 19th to a warm 23.2 °C on the 4th. Last December, Perth Metro recorded a mean minimum temperature of 16.6 °C.

Wind and Sunshine

The highest wind gust recorded in the Perth metropolitan area in December was 76 km/h at several locations during the two thunderstorm events in the first half of the month, and in blustery northeasterlies at Champion Lakes on the 4th.

Perth recorded an average daily sunshine of 10.2 hours per day in December 2011, which was well below the average of 11.6 hours, and the least sunniest December since 9.8 hours per day was recorded in 1983.

Further information

Media
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Extremes in December 2011
Hottest day 40.1 °C at Swanbourne on the 28th
Warmest days on average 30.9 °C at Gosnells City
30.9 °C at Pearce RAAF
Coolest days on average 26.5 °C at Rottnest Island
27.9 °C at Bickley
Coldest day 20.3 °C at Bickley on the 6th
Coldest night 10.0 °C at Jandakot Aero on the 19th
Coolest nights on average 15.2 °C at Bickley
Warmest nights on average 19.0 °C at Rottnest Island
18.3 °C at Swanbourne
Warmest night 25.7 °C at Gosnells City on the 29th
Wettest overall 75.8 mm at Perth Metro
Wettest day 48.8 mm at Pearce RAAF on the 7th
Highest wind gust 76 km/h at Champion Lakes on the 4th
76 km/h at Rottnest Island on the 6th & 12th
76 km/h at Bickley on the 13th

Record highest December daily rainfall
Highest daily rainfall
in December 2011 (mm)
Previous highest
for December
Years of
record
Perth Airport 35.2 on the 13th 27.2 on the 3rd in 1951 68
Pearce RAAF 48.8 on the 7th 34.5 on the 18th in 1952 57
Roleystone 40.0 on the 7th 28.4 on the 27th in 1966 44
Medina Research Centre 26.8 on the 13th 25.2 on the 31st in 1983 29
Swanbourne 29.8 on the 13th 14.2 on the 10th in 2008 19
Garden Island HSF 19.4 on the 7th 7.4 on the 21st in 2008 11



Record highest total December rainfall
Total rainfall
for December 2011 (mm)
Previous highest
for December
Years of
record
Average for
December
Perth Airport 65.8 65.5 in 1951 68 11.2
Pearce RAAF 65.0 53.6 in 1952 49 10.2
Roleystone 67.2 44.4 in 1967 44 15.2
Bickley 41.0 40.6 in 1983 41 13.2
Medina Research Centre 51.8 29.4 in 1983 29 10.6
Swanbourne 67.0 24.8 in 2008 19 10.9
Garden Island HSF 38.8 13.6 in 2005 11 9.7



Record highest December mean daily minimum temperature
Mean daily minimum
temperature
for December 2011 (°C)
Previous highest
for December
Years of
record
Average for
December
Pearce RAAF 17.3 17.1 in 2002 52 14.4
Medina Research Centre 17.7 16.6 in 2002 24 14.9
Jandakot Aero 16.7 16.5 in 1999 21 14.5
Swanbourne 18.3 17.8 in 2002 18 16.4
Bickley 15.2 14.8 in 1999 17 13.4
Garden Island HSF 18.8 18.0 in 2002 10 16.9


Summary statistics for December 2011
Maximum temperatures
for December
(°C)
Minimum temperatures
for December
(°C)
Rainfall
for December
(millimetres)
Mean for
December
2011
Diff
from
average
Highest for
December
2011
Mean for
December
2011
Diff
from
average
Lowest for
December
2011
Total for
December
2011
Average
for
December
Rank of
December
2011
Fraction of
December
average
Bickley 27.9 0.0 36.0 28th 15.2 +1.8 11.5 1st 41.0 13.2 highest 311%
Champion Lakes 29.5   37.9 28th 18.2   14.3 19th 65.8
Garden Island HSF 27.6 +2.4 37.9 28th 18.8 +1.9 15.9 1st 38.8 9.7 highest 400%
Gosnells City 30.9 +0.7 39.6 28th         55.4 11.5 v high 482%
Jandakot Aero 30.1 +1.2 39.1 28th 16.7 +2.2 10.0 19th 39.0 10.5 v high 371%
Medina Research Centre 30.1 +2.2 39.6 28th 17.7 +2.8 12.9 19th 51.8 10.6 highest 489%
Pearce RAAF 30.9 +0.7 38.6 28th 17.3 +2.9 12.0 19th 65.0 10.2 highest 637%
Perth Airport 30.6 +1.7 38.8 28th 17.5 +2.7 11.5 19th 65.8 11.2 highest 588%
Perth Metro 30.5 +1.7 39.9 28th 18.2 +2.0 13.3 19th 75.8 12.8 3rd highest 592%
Rottnest Island 26.5 +1.6 36.3 28th 19.0 +1.5 16.6 7th 70.0 8.2

2nd highest

854%
Swanbourne 29.9 +2.2 40.1 28th 18.3 +1.9 15.8 10th 67.0 10.9 highest 615%

Daily maximum temperature
Central Coast (09)12345678910111213141516171819202122232425262728293031
Bickley29.531.032.831.432.920.322.923.023.327.429.123.520.424.821.225.827.924.323.929.330.630.528.028.928.628.633.236.035.031.828.5
Champion Lakes31.333.034.732.333.822.625.925.126.929.632.124.322.527.223.728.028.824.925.130.329.830.829.430.930.431.034.737.935.830.929.9
Garden Island HSF33.134.735.534.833.323.026.323.023.827.128.523.723.528.027.225.225.923.824.024.723.123.723.225.626.128.733.637.935.025.025.0
Gosnells City32.835.537.035.823.827.426.927.431.433.226.324.928.525.025.530.526.926.831.732.931.032.532.536.939.638.533.031.0
Jandakot Aero32.734.236.135.634.523.226.626.226.329.731.826.223.628.325.927.729.325.625.829.928.929.929.431.431.931.835.639.137.829.829.3
Medina Research Centre33.234.936.936.135.923.827.425.925.929.432.026.723.729.426.527.428.925.325.729.527.928.327.530.429.232.535.439.637.930.730.1
Pearce RAAF31.934.236.136.535.822.928.326.327.530.630.429.423.428.927.228.926.127.031.431.831.830.332.231.631.735.038.637.032.131.0
Perth Airport32.634.336.136.735.823.327.526.127.030.332.326.824.228.427.128.029.426.126.031.330.331.030.231.731.431.635.338.837.231.630.0
Perth Metro32.934.936.437.635.124.227.626.826.830.131.726.323.929.126.528.129.625.526.330.629.230.428.530.930.232.136.139.937.830.829.6
Rottnest Island30.033.233.732.931.921.424.523.423.524.427.423.522.625.125.624.026.023.823.124.724.024.623.624.724.125.529.836.332.325.625.3
Swanbourne33.435.536.936.434.724.127.325.225.830.532.728.324.630.327.728.226.924.825.925.826.726.829.229.832.036.140.135.927.427.1

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
Bickley11.513.614.518.919.515.714.313.714.313.615.016.214.315.615.713.613.713.312.312.916.415.316.813.713.713.114.018.820.319.017.6
Champion Lakes15.617.019.023.923.519.617.815.218.217.018.819.617.318.419.516.917.715.114.316.215.816.016.617.617.316.718.322.424.419.820.0
Garden Island HSF15.917.419.421.122.719.618.518.618.016.519.019.617.619.119.316.616.919.416.116.519.619.419.417.317.516.818.521.621.522.219.8
Gosnells City16.217.119.023.918.317.019.322.017.518.119.517.117.515.513.915.615.615.617.517.018.522.825.720.520.5
Jandakot Aero15.216.918.922.322.519.317.215.317.414.516.618.716.317.618.815.212.614.110.014.213.615.416.416.916.816.215.221.417.818.117.7
Medina Research Centre15.617.119.424.023.118.717.315.917.415.918.120.016.818.418.815.113.616.712.915.014.516.517.116.416.716.418.022.920.020.219.5
Pearce RAAF16.614.819.825.223.818.117.615.517.515.918.817.417.118.119.716.513.512.612.013.314.014.916.716.217.516.818.720.820.618.119.7
Perth Airport15.317.418.522.322.718.317.016.417.715.418.019.517.418.719.216.515.015.411.514.213.716.117.017.117.316.817.619.723.118.019.1
Perth Metro15.417.619.223.221.519.117.917.218.116.618.519.416.918.619.416.716.417.013.316.617.417.017.817.617.516.818.021.821.321.320.3
Rottnest Island16.817.919.722.721.918.916.618.517.917.219.719.816.819.119.316.618.018.717.817.119.119.119.118.017.917.518.922.023.721.420.9
Swanbourne16.217.119.323.621.418.217.516.117.415.818.319.816.417.718.915.916.116.917.316.717.517.117.316.818.122.322.421.320.7

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 - - - - - 5.6 15.6 - - - - - 18.8 0.8 - - - - - - - - 0.2 - - - - - - - -
Champion Lakes - - - 0.4 - 1.8 18.8 11.0 - - - - 33.8 - - - - - - - - - - - - - - - - - -
Garden Island HSF - - - - - 1.0 19.4 - - - - - 18.2 - 0.2 - - - - - - - - - - - - - - - -
Gosnells City - - - - - 14.4 18.6 4.6 0.1 »» »» 0.1 17.0 0.6 - - - - - - - - - - - - - - - - -
Jandakot Aero - - - 0.8 - 1.8 23.6 - - - - 0.4 12.4 - - - - - - - - - - - - - - - - - -
Jarrahdale - - - - - - 22.0 18.6 - - - - 29.2 0.4 - - 0.2 - - - - - - - - - - - - - -
Medina Research Centre - - - - - 1.8 23.2 - - - - - 26.8 - - - - - - - - - - - - - - - - - -
Mundaring




8.0 24.4



1.4 17.8 2.8
















Pearce RAAF - - - - - 15.0 48.8 - - -
0.8 0.4 - -
-
- - - -
- - - - - - - -
Perth Airport - - - - - 9.8 20.8 - - - - - 35.2 - - - - - - - - - - - - - - - - - -
Perth Metro - - - - - 6.4 25.8 - - - - - 43.6 - - - - - - - - - - - - - - - - - -
Roleystone


0.4 0.2 5.2 40.0



0.2 21.0

0.2














Rottnest Island - - - - - 2.2 31.4 - - - - - 36.2 - - - - - - - 0.2 - - - - - - - - - -
Serpentine - - - - - 0.8 18.2 8.0 0.2 - - - 36.8 0.2 - 0.4 - - - - - - - - - - - - - - -
Swanbourne - - - - 0.4 10.2 26.6 - - - - - 29.8 - - - - -


- - - - - - - - - -

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 11 am on Tuesday 3 January 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, as they cannot then be calculated reliably.
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