Monday 1 May 2006

SYDNEY MONTHLY CLIMATE SUMMARY - NSW REGIONAL OFFICE

Dry and sunny with warm days in Sydney during April

April 2006 - Main Points:

• 5th driest April on record with only 9.8mm.
• Daytime maximum temperatures 5th highest on record.
• Many warm days. 7 days above 27°C, highest since 1922 (when 11 days).
• Sunniest April on record averaging 9.2 hours per day.
• Prevailing dry westerly winds caused record low humidity.

Rainfall:   Sydney's total rainfall of 9.8mm was the 5th lowest in 147 years of record and well below the historic April average of 127mm. It was the driest April since 1997 when 5.2mm was recorded. There were only 5 rain days during April, the lowest since 1995.  The historic average is 12 rain days. Much of the rain occurred as light showers and drizzle during the last week of the month, falling mostly in coastal suburbs. Below average rainfall extended throughout metropolitan Sydney during April ranging from 17.6mm at Rose Bay in Sydney's east to only 2mm at Canterbury.

Rainfall over the Warragamba Dam catchment area was also very light and patchy with the whole catchment recording less than 7mm during April.   Recent rainfall over Sydney's catchments can be found on the Sydney Catchment Authority web site http://www.sca.nsw.gov.au/dams/rainfall.html

Temperatures:    The average monthly mean temperature (the average of daytime and night-time temperatures) of 19.5°C was slightly above the historic average of 19.2°C.  It is the 13th consecutive month with above average monthly mean temperatures in Sydney.  Days were generally warm with the average maximum day-time temperature of 24.6°C being well above the historic average of 23.2°C and the 5th highest on record. There were 7 days when the temperature exceeded 27°C, the highest since 1922 (when 11 days over 27°C). The historic average for April is only 2 days over 27°C.

However, Sydney's nights were relatively cool,  due to mostly clear skies and low humidity.  The average minimum temperature of 14.3°C was almost 1°C below the historic average, and the lowest since 1999. Nights were particularly cool in the western suburbs with the occasional light frost in the far west.  On the 23rd the mercury fell to -0.4°C at Richmond and 3.6°C at Prospect Dam, both new records for April.  The previous lowest for Richmond was 1.1°C in April 1934.

The highest temperature at Sydney (Observatory Hill) during April was 33.1°C on the 12th which is the 3rd highest temperature ever recorded in April.  The 12th is also the latest date in April that Sydney has recorded a temperature exceeding 33°C.  The lowest temperature was 9.2°C on the 23rd, the lowest in April for 6 years. Corresponding extremes across the Sydney metropolitan area ranged from 33.6°C at Penrith on the 12th to -0.7°C at Camden on the 23rd.

Sunshine, humidity and evaporation:   With many consecutive clear days, Sydney had its sunniest April on record averaging a plentiful 9.2 hours per day. The previous highest was 8.5 hours per day in 1980 (historic average is 6.9 hours).  The prevailing dry W-NW winds and lack of cloud during the month caused record low humidity levels for April, averaging only 44% at 3pm (historic average 59%).  On the 6th the humidity fell to a very low 17%.  The low humidity and warm days also contributed towards record high pan evaporation, Sydney registering 158mm of evaporation during April (historic average 123mm).

This statement has been prepared based on information available at noon on 1/3/06. Although every effort has been made to check them, it is possible that results may change as new information becomes available.

A note about deciles: Deciles are used to give an element (in this case rainfall or temperature) a ranking. Deciles are calculated by arranging the totals in ascending order (from lowest to highest) then splitting them into 10 equal groups (thus the groups are called deciles). The first group would be in decile range one, the second group in decile range two, etc up to the highest annual totals (highest 10 per cent) being in decile range 10.

Averages: Historic average temperatures are based on the period 1961 to 1990 which is a convention of the World Meteorological Organisation.

Further information: Contact Mike De Salis 02 9296 1542, email: reqnsw@bom.gov.au

A directory of Bureau services is available on poll fax: 1800 630 100

The latest rainfall and temperature maps are available here
Climate averages for New South Wales localities are available here
Daily Weather Observations for selected New South Wales localities are available here