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ARTICLES >> Environment Weather Watch

Weather Watch - August 2011

Posted by Bestprac on Aug 08 2011

by Susan Carn

The weather for me in the last week can be best described by paraphrasing a song: Lows to the left of me, lows to the right, here I am – stuck in the middle with highs!

To explain, parts of both sides of Australia have had some good rain falls in the last month but the Upper Northern agricultural area of SA where I live has been thwarted by pesky high pressure systems! The most annoying of them occurred just as a lovely north west cloudband was approaching – full of promise, only to be compromised by the unseasonally positioned high. Consequently we only received 8mm, when we were hoping for a lot more. Since then there have been more fronts coming up from the south, only to slip away due to blocking highs.

As I have mentioned before, the sub-tropical ridge determines where dry high pressure systems sit, and should follow a seasonal pattern. For example in winter they should be positioned over central Australia thus allowing cold wet systems to come up as far as possible rather than just slipping south.

Recently I read about the continuing trend towards decreasing autumn and winter rainfall over southern Australia. According to research carried out by CSIRO climate scientist, Dr Jorgen Frederiksen, these changes are “due to a large downturn in the intensity of storm formations over at least the last three decades compared with the previous three decades, and these effects have become more pronounced with time."

The following from the CSIRO website states “The research, based on observations and climate modelling, centres on the changes in southern Australian winter rainfall linked to atmospheric circulation changes that are directly associated with storm formation, and particularly rain bearing lows and frontal systems crossing southern Australia. The most important circulation feature associated with winter storm formation is the strength of the sub-tropical jet stream.”

So it seems the signs are pointing towards less rainfall due to this combination of a “reduction in the intensity of storms, the southward shift in storm tracks, changing atmospheric temperatures and reductions in mid-latitude vertical wind shear affecting rainfall" according to Dr Frederiksen.

All a bit depressing really! But I try and remember that a variable climate is just that – variable. It will still rain, it might just be patchier, and less predictable. Which makes the folks at the Bureau of Meteorology work even harder. However, they are always improving their skills and information gathering.

For instance, last week the new weather station at Ceduna was opened. The station uses a vertical wind profiler, which replaces upper air wind observations using weather balloons. The profiler enables continuous reporting of winds from 300m to 5km above the station. It can produce vertical wind profiles every 30 minutes, greatly improving the ability to monitor storms and weather systems, and support accurate and timely forecasts and warnings. The new facilities will help forecasters understand the weather in an area of Australia where data has been relatively sparse.

So there’s some good news. It looks like whatever Mother Nature throws at us, we are at least trying to keep up!

Last changed: Feb 09 2012



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