Monday, 2 November 2009 - Monthly Climate Summary for Canberra rainfall extremes - Product code IDCKGC25x0

Canberra has cloudy, cool October

  • Close to average rainfall
  • Cool to cold days with below average maximum temperatures
  • Coolest October since 2003
  • Mild nights, close to average minimum temperatures
  • Second cloudiest October on record (6.9 hours of sunshine per day)

An archive of previous monthly summaries for Canberra rainfall extremes is also available, as are summaries for other states and many other climate summaries and diagnostics.

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Rainfall

Canberra Airport recorded a total rainfall of 42.4 mm during the month, which is below the historical average of 62.1 mm. This is now the 10th consecutive October with below average rainfall in the ACT and makes it the longest continuous period of below average October rainfall since Canberra records commenced in 1939. Higher falls were recorded in southwestern parts of the city where Tharwa's total was 78.4 mm and Tuggeranong 75.2 mm. Canberra Airport recorded 14 raindays during the month, which is the highest for October since 1976 (when 18 raindays). Normally Canberra would expect around 10 raindays in October.

A number of low pressure troughs during the month with associated thunderstorms caused the majority of the rain over the ACT. The most active was on the 25th when a combined surface and upper low caused thunderstorms and heavy showers in the ACT, especially over the southern ranges.

October monthly totals in Canberra suburbs ranged from a high of 75.2 mm at Tuggeranong AWS in the southwestern suburbs to a low of 41.8 mm at Cook in Belconnen. Higher falls occurred on the ACT ranges where Corin Dam recorded a monthly total of 126.0 mm.

Temperatures

In a marked contrast to September, days were cool and cloudy in the ACT during October. The mean maximum (daytime) temperature at Canberra Airport was 19.0°C, which is 0.4°C below the historical October average of 19.4°C, making it the coolest October since 2003. There were 12 'cold' days (maximum temperature below 16°C), twice the average of 6 days. It is the highest number of cold days in October since 1986 (when 14 days below 16°C). The coldest day was 11.3°C on the 7th, the lowest maximum temperature in October since 23 October 1999. Snow fell in Cooma - Monaro districts south of the ACT on the 7th as well as on the ACT ranges.

Nights were generally cool to mild and close to the October historical average. The mean minimum temperature at Canberra Airport was 6.6°C, or 0.5°C above the October historical average of 6.1°C. Canberra Airport recorded only 4 frosts during the month (minimum temperature below 2°C) below the normal 7 frosts for October. The lowest temperature in Canberra suburbs was −0.3°C at the airport on the 9th. The lowest in the ACT was −3.6°C at Mount Ginini AWS on the 16th.

Wind

Following a marked persistence in W-NW winds in the ACT last month, there was a significant change to predominantly E to S winds during October and a noticeable lack of the usual NW wind. Morning winds were E to S up to 52% of the time compared to the usual 20% from this direction. The highest wind gust in Canberra was 65 km/h at Canberra Airport on the 12th and the highest in the ACT was 80 km/h at Mount Ginini AWS on the 14th.

Other phenomena

There were 3 thunderstorms in the ACT during October, on the 2nd, 11th and 25th. Thunderstorms both on the 2nd and 25th caused some local moderate falls, the highest 24 hour totals being 29.4 mm at Tralee (to 9am on the 3rd) and 25.8 mm at Tharwa (to 9am on the 26th), both in southern regions of the city. Just over the NSW border at Googong Dam, one of Canberra's water catchment reservoirs, 39 mm was recorded in a storm on the 25th, the highest daily fall in the ACT area for the month.

Relative humidity at 9am averaged 72% which is the highest for October since 1992. Due to the increased humidity and rainfall around the ACT, Canberra Airport recorded 5 fogs during October (6th, 7th, 20th, 29th and 30th), twice the historical average and the highest number of fogs for October since 1977. Visibility was briefly reduced to 100 metres on the 6th and 200 metres on the 7th.

October was a cloudy month with several consecutive days having virtually no sun. Only about 3 hours of sunshine was recorded over the 3 days from the 3rd to the 5th. The monthly average was 6.9 hours per day which is the 2nd lowest October monthly total on record for Canberra Airport. The lowest is 6.7 hours per day in 1992. The historic average for October is 8.7 hours per day.

Further information

Mike De Salis
Climate Officer
NSW Climate Services Centre
NSW Regional Office
Bureau of Meteorology
Phone (02) 9296 1555
Email climate.nsw@bom.gov.au

Extremes for the ACT

Hottest day
Highest temperature		 29.0°C at Canberra Airport on the 21st
Warmest days on average
Highest mean daily maximum temperature		 19.0°C at Canberra Airport
Coolest days on average
Lowest mean daily maximum temperature		 18.8°C at Tuggeranong AWS
Coldest day
Lowest daily maximum temperature		 10.3°C at Tuggeranong AWS on the 7th
1.0°C at Mount Ginini AWS on the 14th
Coldest night
Lowest temperature

−0.3°C at Canberra Airport on the 9th
−3.6°C at Mount Ginini AWS on the 16th

Coolest nights on average
Lowest mean daily minimum temperature		 6.6°C at Canberra Airport
Warmest nights on average
Highest mean daily minimum temperature		 6.8°C at Tuggeranong AWS
Warmest night
Highest daily minimum temperature		 13.1°C at Canberra Airport on the 23rd
Wettest overall
Highest total rainfall		 126.0 mm at Corin Dam
107.0 mm at Bendora Dam
78.4 mm at Tharwa General Store
Driest overall
Lowest total rainfall		 41.8 mm at Cook (Springvale Drive)
42.4 mm at Canberra Airport
Wettest day
Highest daily rainfall		 29.4 mm at Tralee (Melrose Farm) on the 3rd
26.8 mm at Tuggeranong AWS on the 3rd
25.8 mm at Tharwa General Store on the 26th
Highest wind gust
 80 km/h at Mount Ginini AWS on the 14th
65 km/h at Canberra Airport on the 12th
65 km/h at Canberra Airport on the 13th

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Records

Nil recorded

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Summaries for the ACT

This table is very wide and may not fit if printed.

Summary statistics for October 2009
Maximum temperatures
for October
(°C)		 Minimum temperatures
for October
(°C)		 Rainfall
for October
(millimetres)
Mean for
October
2009		 Diff
from
average		 Highest for
October
2009		 Mean for
October
2009		 Diff
from
average		 Lowest for
October
2009		 Total for
October
2009		 Average
for
October		 Rank of
October
2009		 Fraction of
October
average
Canberra Airport 19.0 −0.4 29.0 21st 6.6 +0.5 −0.3 9th 42.4 62.1 average 68%
Tidbinbilla Nature Reserve 17.8 −1.3 26.5 21st 4.9 −1.2 −1.0 7th 81.2 85.0 average 96%
Tuggeranong* 18.8 −2.0 28.9 21st 6.8 +0.6 −0.2 7th 75.2

* temperature averages based on short record 1996−2009. No rainfall averages available.

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Notes

This statement has been prepared based on information available at 12 pm on Monday 2 November 2009. 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 20 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.

Further information

Mike De Salis
Climate Officer
NSW Climate Services Centre
NSW Regional Office
Bureau of Meteorology
Phone (02) 9296 1555
Email climate.nsw@bom.gov.au