Friday, 1 August 2008 - Monthly Climate Summary for Canberra rainfall extremes - Product code IDCKGC1xx0

Cold frosty nights, mild days in Canberra during July

Summary

  • Close to average rainfall
  • Close to average maximum and minimum temperatures at Airport site
  • 23 frosts, highest for July since 2002
  • Slightly above average sunshine

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Rainfall

Canberra Airport recorded a total rainfall of 42.4 mm during the month, which is close to average for July. July rainfall totals have exceeded the historical average1 only twice in the past 10 years. There were 15 rain days during the month, compared to the historic average of 10 rain days. However, 5 of the 15 days were condensation from both dew or fog rather than from precipitation. Active cold fronts associated with deep low pressure systems on the 7th and 20th contributed towards most of the month's rainfall.

Monthly totals for the ACT ranged from a high of 142 mm at Mount Ginini AWS in the highlands SW of Canberra while the highest in the Canberra metropolitan area was 53 mm at Tuggeranong AWS. The lowest July total was 35.4 mm at Tralee in southern Canberra.

Temperature

The mean maximum (daytime) temperature at Canberra Airport was 11.7°C, which is only 0.4°C above the historical average1 of 11.3°C. This is now the 10th consecutive July with above average maximum temperatures and ranks 25th highest out of 69 years of record. However, at the Tuggeranong site, the average maximum temperature was 11.6°C which is slightly below the historical average. The lowest maximum temperature in the ACT was −2.0°C at Mount Ginini AWS on the 8th and 28th while the lowest in the Canberra metropolitan area was 8.4°C at Canberra Airport on the 11th.

Nights were generally cool to cold and frosty, especially the last 10 days of the month when consecutive frosts were recorded at the airport site. The mean minimum (overnight) temperature at Canberra Airport was −0.1°C, which is normal for July, and the lowest for 4 years. At the more sheltered Tuggeranong site, the average minimum temperature was −0.9°C or 0.8°C below the historical average July minimum. There were 23 frosts at Canberra Airport during the month, the frostiest July since 2002 and compares to the historical July average of 21 frosts. Slow moving high pressure systems were generally responsible for the clear, calm and frosty nights, especially during the last 10 days of the month.

Extreme low temperatures in the ACT ranged from −7.3°C at Mount Ginini AWS (elev 1760 metres) on the 22nd and −5.3°C at Tuggeranong AWS on the 25th. The mildest night was 7.0°C at Tuggeranong AWS on the 2nd.

Wind

The prevailing wind direction over Canberra during the afternoons was W-NW for nearly 60% of the time, about the normal frequency expected from this direction during July. During the mornings prevailing E-SE winds had a frequency of 26% compared to the usual 7% from this direction. The highest wind gust recorded was 78 km/hr at Canberra Airport on the 1st associated with the passage of two strong cold fronts.

Other phenomena

The amount of sunshine averaged 5.9 hours per day which is slightly above the historic average for July. The frequency of fog was well below average with only 4 fogs reported at Canberra Airport compared to the normal frequency of around 8 fogs. No thunderstorm or hail activity occurred in the Canberra region during the month. Although no snow fell in Canberra, moderate to heavy snow fell on the Brindabella Ranges SW of the city on the 10th, 11th, 18th, 21st and 27th.

Further information

NSW Climate Services Centre
Bureau of Meteorology
Phone (02) 9296 1555
Email reqnsw@bom.gov.au

Extremes for the ACT

Hottest day
Highest temperature		 16.6°C at Tuggeranong AWS on the 14th
Warmest days on average
Highest mean daily maximum temperature		 11.7°C at Canberra Airport
Coolest days on average
Lowest mean daily maximum temperature		 1.3°C at Mount Ginini AWS
11.6°C at Tuggeranong AWS
Coldest day
Lowest daily maximum temperature

−2.0°C at Mount Ginini AWS on 8th & 28th
8.4°C at Canberra Airport on the 11th
Coldest night
Lowest temperature		 −7.3°C at Mount Ginini AWS on the 22nd
−5.3°C at Tuggeranong AWS on the 25th
Coolest nights on average
Lowest mean daily minimum temperature		 −3.5°C at Mount Ginini AWS
−0.9°C at Tuggeranong AWS
Warmest nights on average
Highest mean daily minimum temperature		 −0.1°C at Canberra Airport
Warmest night
Highest daily minimum temperature		 7.0°C at Tuggeranong AWS on the 2nd
Wettest overall
Highest total rainfall		 142.0 mm at Mount Ginini AWS
53.4 mm at Tuggeranong AWS
Driest overall
Lowest total rainfall		 35.6 mm at Tralee (Melrose Farm)
Wettest day
Highest daily rainfall		 37.4 mm at Bendora Dam on the 21st
25.0 mm at Tuggeranong AWS on the 21st
Highest wind gust
 78 km/h at Canberra Airport on the 1st

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Records

Nil reported

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Summaries for the ACT

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

Summary statistics for July 2008
Maximum temperatures
for July
(°C)		 Minimum temperatures
for July
(°C)		 Rainfall
for July
(millimetres)
Mean for
July
2008		 Diff
from
normal		 Highest for
July
2008		 Mean for
July
2008		 Diff
from
normal		 Lowest for
July
2008		 Total for
July
2008		 Normal
for
July		 Rank of
July
2008		 Fraction of
July
normal
Canberra Airport 11.7 +0.4 16.5 14th −0.1 normal −3.5 23rd 42.4 41.3 normal 102%
Tuggeranong AWS** 11.6 −0.6 16.6 14th −0.9 −0.8 −5.3 25th 53.4 40.1 high 133%
Mount Ginini AWS* 1.3   6.0 14th −3.5   −7.3 22nd 142.0

* new station, no historic averages available
** short record, 1996 - 2008 only

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Notes

This statement has been prepared based on information available at 11 am on Friday 1 August 2008. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

1Averages: historic rainfall and temperature averages are based on all available data.

Normals 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 "normal" 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, normal in decile 4 to 7, high in decile 8 or 9 and very high is in decile 10).
The Fraction of normal shows how much rain has fallen this time as a percentage of the long-term mean.

Further information

NSW Climate Services Centre
Bureau of Meteorology
Phone (02) 9296 1555
Email reqnsw@bom.gov.au