Greater Perth in December 2017: Above average rainfall

It was a wet December for the Greater Perth region due to an unseasonal cold front and moderate falls at the mid-month. Both mean maximum and minimum temperatures were above average for most sites.

Above average rainfall across Greater Perth

  • Rainfall totals were mostly in the 20 mm to 40 mm range on the coastal plain, and over 60 mm in the hills, which were generally 200% to 400% above average
  • A cold front and associated deep low pressure system produced rains in the Greater Perth between the 17th and 19th, with many sites recording daily rainfall 10 mm to 30 mm on the 18th
  • Bickley recorded 36.4 mm in the 24 hours to 9am on the 18th, its highest December daily rainfall, and Bickley also recorded its wettest December on record partly as a result
  • Mount Helena near the Perth hills had its wettest December for 26 years

Above average daytime and overnight temperatures

  • Both mean maximum and mean minimum temperatures were above average for most sites, and temperatures were 1 °C to 2 °C warmer than normal at Perth Airport and Pearce RAAF
  • Perth Airport recorded a four-day hot spell with daily maximum temperatures at or above 35 °C from the 8th to the 11th, which was the earliest such hot spell for 45 years, since 7 to 11 December 1972 when a run of five days at or above 35 °C was recorded
  • Pearce RAAF recorded the highest daily minimum temperature of the month in Perth with 23.8 °C on the 9th, followed the next day by the highest daily maximum temperature in Perth for the month with 39.4 °C

Perth Metro

  • Total rainfall for Perth Metro was 40.6 mm, which is 310% above the long-term December average, and the wettest December for six years, since 75.8 mm was recorded in December 2011
  • The mean maximum temperature for Perth Metro was 29.7 °C, which is 0.6 °C above average and the warmest December for four years, since a mean maximum of 30.5 °C was recorded in December 2013
  • Perth Metro recorded a total of five days with temperatures at or above 35 °C, close to the average, the hottest day being 37.7 °C on the 10th
  • The mean daily minimum temperature for Perth Metro was 16.7 °C, which is 0.4 °C above average and the highest for four years, since a mean minimum of 16.7 °C was also recorded in December 2013
  • Perth Metro recorded a total of 3 mornings with minimum temperatures at or above 20 °C, close to the long-term average, the warmest morning being the 9th with a minimum of 21.8 °C recorded

Further information

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Extremes in December 2017
Hottest day 39.4 °C at Pearce RAAF on the 10th
Warmest days on average 32.0 °C at Pearce RAAF
Coolest days on average 25.1 °C at Rottnest Island
27.2 °C at Mandurah
Coldest day 16.7 °C at Bickley on the 18th
Coldest night 9.1 °C at Bickley on the 1st
Coolest nights on average 13.9 °C at Bickley
Warmest nights on average 17.7 °C at Rottnest Island
17.5 °C at Mandurah
Warmest night 23.8 °C at Pearce RAAF on the 9th
Warmest on average overall 24.0 °C at Pearce RAAF
Coolest on average overall 21.2 °C at Bickley
Wettest overall 66.6 mm at Huntly
Wettest day 36.4 mm at Bickley on the 18th
Strongest wind gust 89 km/h at Ocean Reef on the 17th

Record highest December daily rainfall
New record
(mm)
Old
record
Years of
record
Bickley 36.4 on the 18th 35.6 on the 31st in 1983 47
Pickering Brook North 29.8 on the 18th 25.6 on the 13th in 2016 30



Record highest December total rainfall
New record
(mm)
Old
record
Years of
record
Average for
December
Bickley 64.4 41.0 in 2011 47 14.9

Highest December total rainfall for at least 20 years
Observed
(mm)
Most recent
higher
Average for
December
Mount Helena 52.0 61.0 in 1991 13.4

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




Summary statistics for December 2017
Maximum temperatures
(°C)
Minimum temperatures
(°C)
Rainfall
(millimetres)
Mean for
December
2017
Diff
from
average
Highest for
December
2017
Mean for
December
2017
Diff
from
average
Lowest for
December
2017
Total for
December
2017
Average
for
December
Rank of
December
2017
Fraction of
December
average
Bickley 28.5 +0.5 35.3 10th 13.9 +0.3 9.1 1st 64.4 14.9 highest 432%
Garden Island HSF 25.4 0.0 35.1 3rd 17.5 +0.3 13.6 1st 24.0 11.5 high 209%
Jandakot Aero 29.7 +0.7 37.0 10th 15.8 +1.2 11.2 19th 27.2 11.0 high 247%
Mandurah 27.2 +0.2 35.1 3rd 17.5 +0.4 13.3 1st 33.8 17.4 high 194%
Millendon (Swan Valley) 31.3   38.2 10th 15.7   11.2 18th 35.6
Pearce RAAF 32.0 +1.7 39.4 10th 15.9 +1.4 11.4 2nd 36.6 11.3 high 324%
Perth Airport 30.6 +1.6 38.4 10th 16.4 +1.5 11.9 2nd 28.6 11.4 v high 251%
Perth Metro 29.7 +0.6 37.7 10th 16.7 +0.4 12.4 18th 40.6 13.1 v high 310%
Rottnest Island 25.1 +0.1 34.7 3rd 17.7 +0.1 11.4 18th 39.8 11.6 high 343%
Swanbourne 27.5 -0.4 35.9 3rd 17.3 +0.8 13.4 18th 13.6 11.9 average 114%
Note: Observations for “Perth Metro” are taken from the current site at Mount Lawley (Bureau number 009225).
Comparisons are made against combined data from the current site (which opened in early 1993) and the previous site at Perth Regional Office (009034), which ran from 1876 to early 1992.

Daily maximum temperatures for December 2017
12345678910111213141516171819202122232425262728293031
Bickley25.932.632.621.026.026.527.032.431.935.335.028.824.527.529.927.717.816.722.627.833.631.829.732.132.026.025.327.329.732.532.9
Garden Island HSF25.631.235.123.022.622.725.031.331.033.432.722.822.022.522.823.920.920.122.624.424.024.025.928.126.323.121.621.725.828.023.5
Gosnells City29.035.738.025.028.030.035.537.837.029.031.021.521.424.530.037.032.535.129.031.035.034.0
Jandakot Aero27.334.335.624.826.928.929.335.634.137.036.828.125.227.028.927.721.621.323.328.935.031.330.934.331.826.425.827.428.834.732.8
Karnet21.530.036.028.024.028.518.017.523.027.724.525.327.0
Mandurah25.330.735.122.625.225.528.033.230.132.132.425.924.123.826.325.320.120.522.526.432.929.929.230.728.924.724.024.325.629.929.3
Medina Research Centre28.034.035.824.025.728.330.336.034.836.836.325.724.725.7
Millendon (Swan Valley)29.335.635.625.229.629.429.735.833.538.237.730.327.230.132.730.622.321.724.931.037.034.532.835.334.628.227.128.730.735.934.6
Pearce RAAF30.136.036.227.429.130.030.636.434.839.438.730.227.531.332.930.622.721.925.032.238.935.433.636.435.028.528.129.431.936.835.3
Perth Airport28.535.636.024.628.028.929.835.835.238.437.928.327.328.230.528.821.721.124.229.736.732.531.535.133.127.426.528.830.035.433.6
Perth Metro27.834.535.525.127.327.929.035.233.237.737.627.625.327.629.527.821.920.923.428.936.131.730.533.732.526.425.225.828.334.732.0
Rottnest Island23.128.834.723.323.323.123.329.128.433.531.423.522.623.423.124.020.520.821.325.524.824.524.625.928.724.523.222.323.626.024.7
Swanbourne25.934.035.924.224.425.126.635.134.535.034.224.623.625.125.525.222.120.922.828.132.326.127.130.627.925.023.923.325.530.826.1
Values are the maximum temperature, usually in the 24 hours from 9 am on the day indicated,
and typically occurred in the afternoon of that day.
Temperatures coloured according to 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 Grey outline marks highest
and lowest for the period

Daily minimum temperatures for December 2017
12345678910111213141516171819202122232425262728293031
Bickley9.112.615.916.515.312.511.112.318.018.419.917.912.112.813.914.712.09.59.610.914.517.013.413.618.114.312.012.612.313.815.7
Garden Island HSF13.616.220.918.618.116.415.017.221.418.618.420.616.616.517.019.015.414.514.815.116.419.217.118.121.419.716.716.315.417.419.9
Gosnells City13.116.020.919.519.017.015.023.522.520.514.416.712.512.615.517.517.916.914.518.020.5
Jandakot Aero12.912.219.818.817.714.914.415.821.416.518.118.313.413.414.714.614.813.011.213.414.618.716.617.419.216.013.514.314.417.118.9
Karnet16.616.812.510.311.513.012.512.512.0
Mandurah13.316.320.518.418.316.114.516.821.621.822.020.816.815.716.318.415.413.513.914.417.120.517.317.921.419.016.515.714.617.119.2
Medina Research Centre12.314.518.517.917.914.414.016.421.016.719.018.913.313.414.8
Millendon (Swan Valley)13.311.421.019.419.016.614.816.123.216.617.619.813.414.014.313.115.611.211.712.714.418.216.917.417.614.212.114.012.816.419.4
Pearce RAAF13.911.422.519.319.116.015.014.823.817.118.420.113.313.213.712.315.712.312.913.115.416.316.517.717.714.612.814.813.116.819.2
Perth Airport13.011.920.119.519.016.714.616.022.017.820.319.914.715.514.214.615.212.012.013.614.517.417.017.519.715.414.515.715.617.319.7
Perth Metro13.113.220.619.119.016.514.916.221.816.818.720.315.815.416.416.615.312.413.815.014.316.617.018.118.917.915.715.615.517.619.1
Rottnest Island14.217.120.618.117.916.515.217.821.819.720.119.617.917.017.918.914.511.415.615.818.019.817.718.420.718.917.616.716.118.220.2
Swanbourne13.515.721.318.518.715.615.117.023.320.820.019.615.615.016.117.215.313.414.215.216.519.617.118.320.519.116.115.314.518.019.6
Values are the minimum temperature, usually in the 24 hours to 9 am on the day indicated,
and typically occurred that morning.
Temperatures coloured according to 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 Grey outline marks highest
and lowest for the period

Daily rainfall for December 2017
12345678910111213141516171819202122232425262728293031
Anketell - - - 7.8 1.2 - - - - 0.6 - - - - - - 3.2 13.0 8.4 - - - - - - - - - - - -
Armadale - - - 7.8 - - - - - - - - - - - - - 18.4 6.0 - - - - - - - - -


Bickley - - - 7.2 0.2 - - - - - - - - - - - 7.0 36.4 13.6 - - - - - - - - - - - -
Bungendore - - - 7.0 - - - - - - - - - - - - 6.8 28.8 5.6 - - - - - - - - - - - -
Chidlow - - 4.8 0.4 - - - - - - - - - - - 28.0 4.8











Forrestdale - - - 7.0 0.2 - - - - 1.4 - - - - - - 4.0 13.2 5.6 - - - - - - - - - - - -
Garden Island HSF - - - 9.0 1.0 - - - - 0.2 - - - - - - 1.6 7.0 5.2 - - - - - - - - - - - -
Gosnells City - 7.8 0.5 - - - - 15.8 3.4 - - - - - - - - - - - -
Huntly - - - 5.8 0.8 - - - - - - - - - - - 7.0 28.8 24.2 - - - - - - - - - - - -
Jandakot Aero - - - 6.4 0.2 - - - - - - - - - - - 4.4 10.4 5.8 - - - - - - - - - - - -
Jarrahdale - - - 8.6 0.2 - - - - - - - - - - - 8.8 35.6 8.2 0.2 0.2 - - - - - - - - - -
Karnet

- - -



- - - - 21.2 14.5 - -




- - - - -
Karragullen North - - - 8.2 - - - - - - - - - - - - 7.2 29.2 11.9











Maida Vale - - - 5.0 1.0 - - - - - - - - - - - 5.6 21.6 6.4 - - - - - - - - - - - -
Mandurah - - - 14.2 3.0 - - - - - - - - - - - 2.6 11.0 3.0 - - - - - - - - - - - -
Midland - 6.6 0.4 - - - 0.4 - - - - 20.2 - 5.2 - - - - - - - - - - -
Millendon (Swan Valley) - - - 6.0 0.8 - - - - 0.4 - - - - - - 5.2 16.2 7.0 - - - - - - - - - - - -
Mount Helena


4.4











5.4 29.0 13.2











Mount Solus - - - 6.0 0.2 - - - - - - - - - - - 4.2 26.6 8.8 - - - - - - - - - - - -
Muchea - - - 7.8 - - - - - - - - - - - - 5.2 15.8 10.4 - - - - - - - - - - - -
Mundaring - - - 5.6 1.0 - - - - 0.4 - 0.6 - - - - 6.2 24.4 7.8











Noble Falls



1.2





2.2



3.6 20.6 6.0











Pearce RAAF - - - 5.0 1.2 - - - - - - - - - - - 4.0 19.6 6.6 0.2 - - - - - - - - - - -
Perth Airport - - - 5.0 0.2 - - - - - - - - - - - 2.8 15.8 4.8 - - - - - - - - - - - -
Perth Metro - - - 7.4 - - - - - - - - - - - - 2.6 22.2 8.4 - - - - - - - - - - - -
Pickering Brook


6.0











5.4 19.8 10.2











Pickering Brook North - - - - 5.6 0.6 - - - - - - - - - - 7.8 29.8 11.0 - - - - - - - - - - - -
Pinjarra Refinery - - - 6.4 0.2 - - - - - - - - - - - 3.6 18.0 4.0 - - - - - - - - - - - -
Pinjarra South - - - 5.8 0.6 - - - - - - - - - - - 2.2 14.4 5.8 - - - - - - - - - - - -
Roleystone - - - 7.8 - - - - - - - - - - - - 6.4 22.6 6.8











Rottnest Island - - - 18.8 2.4 - - - - 1.4 - - - - - - 4.0 11.8 1.2 - - - - - - - 0.2 - - - -
Serpentine - - - 6.0 0.2 - - - - - - - - - - - 1.6 28.6 4.4 - - - - - - - - - - - -
Swanbourne - - - 1.4 7.8 0.2 - - - - - - - - - - 0.8 1.6 1.0 0.6 - 0.2 - - - - - - - - -
Wanneroo - 8.6 - - - - 1.8 - - - - 7.0 3.0











Werribee - - - 4.6 1.2 - - - - - - 1.0 - - - - 1.8 12.8 4.6 - - - - - - - - - - - -
Whiteman Park - - - 7.2 - - - - - 0.6 - - - - - - - 19.6 8.2











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 shown 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).
Rainfalls coloured
according to the amount
0 1.0 5.0 10.0 15.0 25.0 50.0 100 150 200 300 400 600 millimetres

Notes

The Monthly climate summary, generally published on the first working day of each month, lists the main features of the weather in Greater Perth using the most timely and accurate information available on the date of publication; it will generally not be updated. More extensive discussion of significant weather events, along with later information and data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review.

In September 2017 this summary was broadened to include data from observing sites in or near the Greater Perth “Greater Capital City Statistical Area” (GCCSA). The Australian Bureau of Statistics designed the GCCSAs to “include the population within the urban area of the city, as well as people who regularly socialise, shop or work within the city, and live in small towns and rural areas surrounding the city. It is important to note that GCCSAs do not define the built up edge of the city. They provide a stable definition for these cities and are designed for the output of a range of social and economic survey data.

This statement has been prepared based on information available at 9 am on Tuesday 9 January 2018. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

In some situations, some or all of the rainfall is in the form of hail or snow. In these cases the totals given are for the water equivalent: the depth of liquid water that results from melting any frozen precipitation. There can be significant 'undercatch' of snow in strong winds, meaning the true precipitation can be higher than that reported.

Averages for individual sites 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.

Where temperature area averages are mentioned, they are derived from the ACORN-SAT dataset.

Further information

Media
(03) 9669 4057
Enquiries