Perth in April 2015: a mild month with average rainfall

Rainfall was near average to above average across the Perth metropolitan area in April with most of the rainfall recorded the second week of the month. The highest daily rainfall in the Perth area was 27.2 mm at Karnet on the 10th, and Bickley recorded the highest monthly total in Perth with 81.6 mm. Perth Metro recorded 54.0 mm on nine rain days, which is just above the long-term average of 43.8 mm, and the wettest April in three years, since 69.2 mm was recorded in April 2012.

Sites across the Perth area saw seven consecutive rain days between the 7th and 13th due to a slow moving low pressure system and persistent cloudbands. It was the longest wet spell in April at Perth Metro for 35 years, since seven consecutive days of rain were reported from 17 to 23 April 1980. The record April wet spell at Perth Metro is 15 consecutive wet days in 15 to 29 April 1926.

Mean maximum temperatures for April were mostly near average in Perth, although cooler than normal maxima were reported in the hills. Mean maximum temperatures ranged from the low-twenties in the hills to the mid-twenties on the coastal plain and offshore islands. The mean maximum temperature of 25.4 °C at Perth Metro was slightly below the long-term average of 25.9 °C and the mildest April for five years, since a mean maximum of 25.0 °C was recorded in 2010.

Days were warm to hot for the first five days of the month and were warm between the 18th and 22nd, with daily maxima often in the high-twenties for coastal plain sites. Mild days were experienced from the 6th to 17th, and from the 23rd to the end of the month for most sites, though a few cool days with maxima below 20 °C were observed in the hills. The hottest day of the month in Perth was the 5th for most sites, however a daily maximum temperature of 32.3 °C at Pearce RAAF on the 4th was the highest temperature for April 2015 in the Perth metropolitan area. Most sites saw their mildest day on the 7th, and a daily maximum of 16.1 °C at Bickley on the 7th was the lowest maximum temperature of the month in Perth.

Mean minimum temperatures were mostly near average in Perth, though Bickley recorded below average minima. Mean minima ranged from the low-teens in the hills, to the low to mid-teens on the coastal plain, to the mid-teens on the offshore islands. Perth Metro recorded a mean minimum temperature of 13.5 °C, which is slightly below the long-term average of 13.8 °C, and the coolest April for six years, since a mean minimum of 13.5 °C was also recorded in April 2009.

Most nights were mild to warm with minimum temperatures generally in the teens, though the second half of the month was cooler than the first. Cool nights were reported at some sites from the 15th to 18th, and 21st to 27th, and Jandakot Aerodrome recorded the lowest temperature of the month with 6.3 °C on the 17th. The mildest night for most sites was the 10th as minima close to or above 19.0 °C were commonly recorded, however the highest minimum temperature in the metropolitan area in April was 19.6 °C, at both Rottnest Island on the 4th and Garden Island on the 11th.

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Extremes in April 2015
Hottest day 32.3 °C at Pearce RAAF on the 4th
Warmest days on average 26.1 °C at Pearce RAAF
Coolest days on average 22.3 °C at Bickley
Coldest day 16.1 °C at Bickley on the 7th
Coldest night 6.3 °C at Jandakot Aero on the 17th
Coolest nights on average 11.7 °C at Bickley
Warmest nights on average 16.7 °C at Rottnest Island
14.9 °C at Swanbourne
Warmest night 19.6 °C at Rottnest Island on the 4th
19.6 °C at Garden Island HSF on the 11th
19.3 °C at Jandakot Aero on the 10th
19.3 °C at Swanbourne on the 11th
Warmest on average overall 20.3 °C at Swanbourne
Coolest on average overall 17.0 °C at Bickley
Wettest overall 81.6 mm at Bickley
Driest overall 34.8 mm at Rottnest Island
40.0 mm at Jandakot Aero
Wettest day 27.2 mm at Karnet on the 10th
Strongest wind gust 72 km/h at Perth Airport on the 5th
72 km/h at Perth Airport on the 6th




Summary statistics for April 2015
Maximum temperatures
(°C)
Minimum temperatures
(°C)
Rainfall
(millimetres)
Mean for
April
2015
Diff
from
average
Highest for
April
2015
Mean for
April
2015
Diff
from
average
Lowest for
April
2015
Total for
April
2015
Average
for
April
Rank of
April
2015
Fraction of
April
average
Bickley 22.3 -1.4 27.3 3rd 11.7 -1.0 7.8 24th 81.6 55.7 high 146%
Garden Island HSF 24.0 +0.1 30.0 5th 15.9 -0.2 11.5 24th 49.6 41.5 high 120%
Jandakot Aero 25.2 -0.6 30.0 5th 12.8 +0.4 6.3 17th 40.0 42.3 average 95%
Medina Research Centre 25.3 -0.4 30.0 5th 13.7 +0.3 6.7 17th 44.1 39.4 average 112%
Pearce RAAF 26.1 -0.3 32.3 4th 14.1 +0.7 8.4 18th 54.6 34.8 high 157%
Perth Airport 25.7 +0.1 30.5 5th 13.4 +0.4 8.4 17th 53.2 40.7 average 131%
Perth Metro 25.4 -0.5 30.4 5th 13.5 -0.3 8.9 22nd 54.0 43.8 average 123%
Rottnest Island 23.6 -0.2 26.7 20th 16.7 -0.6 12.2 24th 34.8 35.9 average 97%
Swanbourne 25.7 +0.3 31.8 5th 14.9 -0.3 11.1 24th 57.8 39.2 high 147%

Daily maximum temperatures for April 2015
123456789101112131415161718192021222324252627282930
Bickley24.024.827.326.626.721.616.121.421.620.920.019.720.919.419.619.822.223.824.625.125.425.022.317.719.721.622.723.020.824.1
Garden Island HSF27.026.726.223.130.024.920.124.223.722.322.721.020.422.521.122.220.225.928.427.424.624.723.321.623.325.225.924.223.025.6
Gosnells City27.027.929.829.630.225.020.525.524.324.223.023.223.624.827.428.828.828.527.421.523.625.527.3
Jandakot Aero27.027.529.029.630.024.820.224.424.724.123.922.822.822.922.623.223.426.828.428.227.926.826.120.723.124.626.125.323.226.8
Medina Research Centre27.728.029.028.130.025.019.725.124.522.023.522.022.023.122.523.623.327.329.029.128.328.025.522.024.025.026.225.523.6
Pearce RAAF27.828.630.932.331.025.620.925.725.826.825.623.323.423.823.623.225.427.126.927.928.228.326.422.123.124.926.525.724.628.4
Perth Airport27.528.130.030.130.525.120.424.925.425.123.523.023.722.923.223.424.927.028.027.928.327.426.021.823.124.626.125.724.527.8
Perth Metro27.727.729.228.730.424.920.724.724.524.123.522.223.423.322.823.224.227.128.228.128.227.126.021.623.224.925.725.424.926.6
Rottnest Island24.125.126.624.026.424.020.524.823.622.823.421.121.622.520.020.721.925.126.326.725.624.423.220.521.723.325.124.323.126.0
Swanbourne28.628.828.426.531.825.320.824.324.824.424.122.722.924.323.924.122.928.328.829.126.725.927.422.324.025.726.526.524.925.8
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 April 2015
123456789101112131415161718192021222324252627282930
Bickley11.410.712.515.813.613.112.112.614.517.014.213.913.011.89.78.08.710.911.311.410.910.811.57.88.48.29.210.613.015.7
Garden Island HSF15.515.917.218.416.817.015.116.318.719.419.617.215.917.212.812.912.414.516.717.016.612.615.111.512.913.715.516.618.319.1
Gosnells City15.115.517.314.017.516.315.316.518.414.616.613.513.113.016.516.517.113.815.112.513.013.5
Jandakot Aero12.213.812.113.216.816.514.916.017.019.317.216.310.011.39.89.96.37.714.014.78.29.410.210.512.410.710.814.511.615.7
Medina Research Centre12.414.614.613.016.516.014.115.318.119.018.016.511.414.710.611.46.711.615.915.012.57.912.510.211.012.012.515.013.518.7
Pearce RAAF14.015.513.914.817.316.615.516.318.219.214.915.611.210.713.011.210.38.415.816.814.110.79.811.011.912.415.115.815.717.5
Perth Airport14.514.613.313.517.316.814.415.717.219.013.415.911.311.812.311.28.49.014.813.913.99.010.310.711.812.311.114.313.416.8
Perth Metro14.314.712.914.017.316.814.516.317.619.116.916.612.113.612.512.39.39.314.312.49.78.910.311.311.911.310.014.813.616.6
Rottnest Island16.016.518.619.617.816.215.217.219.019.019.116.916.717.714.113.914.715.517.017.918.017.416.712.213.614.916.316.718.619.4
Swanbourne13.615.115.215.317.316.914.316.118.019.119.316.414.015.611.312.312.012.415.415.914.311.812.311.112.312.613.415.617.719.2
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 April 2015
123456789101112131415161718192021222324252627282930
Bickley - - - - - - 11.8 24.6 5.4 23.4 2.0 11.2 2.2 0.2 0.6 - - - - - - - - - - - - 0.2
Garden Island HSF - - - - - - 12.2 5.4 0.4 23.4 2.4 4.8 0.6 - 0.4 - - - - - - - - - - - - - - -
Gosnells City - - 6.0 10.0 18.6 0.5

- - - - - - - - - - - - -
Jandakot Aero - - - - - - 5.6 4.8 1.4 16.4 0.6 9.2 1.8 - 0.2 - - - - - - - - - - - - - - -
Jarrahdale - - - 0.2 0.2 - 3.8 2.6 0.6 26.2 10.8 12.0 0.4 0.2 0.6 0.2 0.2 - 0.2 - 0.2 0.2 0.2 - - - - - - 0.2
Medina Research Centre - - - - - - 10.0 4.0 1.0 14.6 3.8 9.2 0.8 0.2 0.4 - - - - - - - - - - - - - - 0.1
Mundaring - - - - - - 15.0 24.0 3.8 12.4 2.8 12.0 1.8 0.2 0.4 - - - - - - - - - - - - - - 1.2
Pearce RAAF - - - - - - 4.2 23.2 7.6 9.2 0.4 8.2 1.6 - - - - - - - - - - - - - - - - 0.2
Perth Airport - - - - - - 7.2 16.8 3.6 14.2 1.4 8.0 1.8 - 0.2 - - - - - - - - - - - - - - -
Perth Metro - - - - - - 9.0 12.4 3.2 12.4 0.6 14.8 1.0 - 0.2 - - - - - - - - - - - - - - 0.4
Roleystone - - - - - - 8.4 8.8 3.2 22.4 8.4 12.2 - - 1.8 - - - - - - - - - - - - - - 0.4
Rottnest Island - - - - - - 8.2 4.8 0.4 17.2 0.2 3.0 0.6 - 0.4 - - - - - - - - - - - - - - -
Serpentine - - - - - - 7.4 5.2 0.6 17.6 3.6 6.6 1.0 - 0.4 - - 0.2 - - - - - - - - - - - -
Swanbourne - - - - - - 12.6 16.6 2.0 14.0 0.8 11.2 0.2 - 0.4 - - - - - - - - - - - - - - -
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

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.

A Climate Summary is generally published on the first working day of each month.

This statement has been prepared based on information available at 9 am on Friday 1 May 2015. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

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.

The ACORN-SAT dataset is used for temperature area averages.

Further information

Media
(03) 9669 4057
Enquiries