Re: La ~ Nina and her effect on the Australian storm season / General weather

December 2010 storm and rainfall records for Blacktown and Sydney

I have compiled the daily weather records for the month of December for my local area being Blacktown. Of interest, the following is noted:-

a) There were three thunderstorms on 2 days. In terms of trends since 1998, the number is lower but not the lowest. There were fewer storms in December 1999, none in December 2002, and 2 in December 2003 and 2009. During the La Nina year of 2007, there were 6 storms on 5 days. It is hard to identify any specific trends occurring for my local area. December 2004 saw more storms than normal for my local area.

Note:- I did not hear any thunder or see any lightning from the rain event of 26/12/2010.

b) It reached 30C on 11 days but the hottest day was on the 31/12/10 when the maximum temperature for the day reached 33.3C (Prospect Weather Station). There have been 23 days since 1/10/2010 when the maximum temperature for the day has reached 30C and the hottest day this season to 31/12/2010 was on 14 November when the maximum temperature reached 33.7C.

One noticeable conclusion for the 1 October to 31 December period at least for my local area is that the maximum temperature has not reached 35C and there is a total absence of very hot days. This is a big contrast to 2009.

c) Rainfall was above normal. Weather Station Number 67026 at Collins Street Seven Hills (Closest to me) recorded 97 mm for the month. The median is 58.5 mm and the mean is 70.4 mm. Rainfall was above average and it rained on 9 days.

Sydney rainfall for 2010

When tallying rainfall for Sydney, I have discovered that while much of New South Wales enjoyed a wet year being wetter than normal, parts of Sydney had rainfall below average for the year. With a La Nina effect in place, above average rains fell in some parts of Sydney such as Campbelltown and Penrith but not Parramatta, Sydney and Terrey Hills (Refer to the second table attached). At Prospect, rainfall for 2010 was 1.8 mm below average (effectively an average year for rainfall).

Looking at Models and information statements, La Nina has now peaked and should now start to weaken. It should hold through to the end of summer and continue to weaken thereafter.

I have prepared 2 tables in the attachment for viewing compiling the data from the local weather stations (Bureau of Meteorology Station sites) and through my own observations. The tables are produced 1/1/2011.

Harley Pearman

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