Friday 2 January 2009 - Monthly Climate Summary for Perth - Product Code: IDCKGC11LO

Another slightly cooler than average December for Perth

Mean daily maximum temperature - near average: Perth's mean daily maximum temperature in December was 27.8°C, compared with the long-term average of 28.7°C. Daily maxima ranged from a mild 21.9°C on the 10th to a hot 39.0°C on the 30th.  Last year Perth recorded a mean December maximum of 27.7°C.  

Mean daily minimum temperature - near average: Perth's mean daily minimum temperature in December was 15.6°C, compared with the long-term average of 16.2°C.  Daily minima ranged from a mild 12.2°C on the 2nd to a warm 21.6°C on the 31st. 

December Rainfall - near average: The city received 11.6 mm of rainfall over 7 days in December, compared with the long-term average of 13 mm on about 4 days.  Historically, December rainfall has ranged from zero on five occasions, to 80.7 mm in 1951. Last December Perth registered 18.0 mm on 7 days.

Annual rainfall - near average: The total rainfall for 2008 for Perth was 807.8 mm on 117 days, compared with the long-term average of 855 mm on about 111 days. Last year 2007, Perth recorded 703.0 mm on 117 days.

December monthly mean temperature and sunshine
Element

2008

 Long- term Average

Highest

 Year

Lowest

 Year Records Commence
Maximum
Temperature (°C)
27.8
28.7
31.7
1931
23.7
2005
1897
Minimum
Temperature (°C)
15.6
16.2
19.6
1977
13.9
2005
1897
Sunshine
(hours per day) #
11.7
11.6
12.6
2000
8.0
1925
1898
December rainfall and rain days
Element 2008 Long-term Average Highest Year Lowest Year Records Commence
Rainfall (mm)
11.6
13
80.7
1951
0.0
5 years
1876
Rain days
7
3.9
14
1913/1944
0
5 years
1876

# This is a preliminary figure based on the available data at the time of issue of this summary. Please check updated mean sunshine hours from Daily Weather Observations for Perth in early January

December daily extremes
Element 2008 Date Extreme Date

Records Commence
Highest daily maximum (°C)
39.0
30/12/2008
44.2
26/12/2007
1897
Lowest daily maximum (°C)
21.9
10/12/2008
14.9
17/12/1952
1897
Highest daily minimum (°C)
21.6
31/12/2008
27.1
18/12/1979
1897
Lowest daily minimum (°C)
12.2
02/12/2008
7.9
07/12/2007
1897
Wettest 24 hours to 9am (mm)
4.2
11/12/2008
46.7
03/12/1951
1876

Climate of Perth in January

It is midsummer in Perth in January, and days are generally sunny and either warm or hot. The low humidity that generally occurs on days of high temperature makes conditions more tolerable. Sea-breezes that blow across the coastal plain on most afternoons moderate the temperature. Hot spells, usually of two or three days duration, are commonly followed by milder conditions. On average, January is Perth's driest month with 10 mm of rain falling on about two days.

January mean temperatures and sunshine
Element Average Highest Year Lowest Year

Records
Commence
Maximum temperature
(°C)
30.5
34.4
1962
26.3
1939
1897
Minimum temperature
(°C)
17.7
20.9
1978
15.6
3 years
1897

Sunshine
(hours per day)
11.6
12.6
1974
8.3
1920
1898
January and rain days
Element
Average
Highest
Year
Lowest
Year
Records Commence
Rainfall (mm)
10
139.0
2000
0.0
13 years
1876
Rain days
2.3
8
1916/90
0
13 years
1876

January daily extremes
Element
Highest
Date
Lowest
Date
Records Commence
Maximum temperature (°C)
45.8
31/01/1991
19.7
* Twice
1897
Minimum temperature (°C)
27.8
21/01/1989
8.9
25/01/2001
1897
Rainfall 24 hours to 9am (mm)
104.0
22/01/2000
n/a
n/a
1876

* Denotes lowest January maximum temperature on record has occurred on the following dates: 19 January 1939 and 3 January 2007.

Very hot days in January: On average, Perth can expect one day when the maximum temperature is 40°C or higher. The greatest number of such days in January was four in 1961, 1965 and 1968. The last time Perth recorded such a day in January was on 17 January 2008 when 41.3°C was recorded.

Hot days in January: On average, Perth can expect twelve days when the maximum temperature is 32 degrees or higher. The highest number of such days in January was 24 in 1962, when the record highest mean maximum temperature for January (34.4 degrees) was set.

Note: 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 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.

Further information:
John Relf (JR), or Glenn Cook tel: (08) 9263 2222 during business hours.