THE past 10 days of September produced a weather feature we have not seen all this winter - a band of rain crossing from the north-west of the country to the eastern seaboard.
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The rain fell in a band that stretched from Broome in northern WA via Alice Springs and Birdsville to Brisbane and the falls varied from five to 30 millimteres of rain. (check out the BOM site for: http://www.bom.gov.au/climate/maps/).
Maps can be viewed as averages for the week or month or also as a daily loop. Also have a look at the temperature maps.
Contrary to the climate indicators (IOD, SOI, SAM etc) this upper trough moved slowly across the country with best falls west and east of Alice Springs. This was not a traditional north-west cloud band, rather it was a one-off upper trough system.
The rainfall map for the month also shows the tantalising strip of frontal rainfall following the coast from Perth to Adelaide, Melbourne, Sydney to Brisbane and not really penetrating further than 100km from the ocean!
For the month of October, NSW rainfall is most variable in the north-west areas and south-east regions of the state. The north-west areas of the state vary with showers and thundery outbreaks with surface and upper troughs that can come from the north or northeast.
The rainfall amounts in that area are not huge and hence any reasonable rain will be a significant variation to the long term mean.
The south-east regions' rainfall vary with an increase in frontal activity; some fronts coming over the mountains from the west and some coming around the coast from Gippsland and Bass Strait.
This month is when the inland heats up and that in turn blocks the frontal activity from pushing very far from the coast.
The fronts become coastally trapped and run up the NSW coast as a southerly change, not the wintertime west-southwest change.
Low pressure systems in close to the NSW south coast can bring significantly more rain, but they also play a major role in bushfire weather further north with warm, dry and gusty offshore westerly winds further north - increasing the bushfire potential dramatically with drought conditions.
October is the month of the change from winter to summer.
In regular years, intense low pressure systems would be near Tasmania and the first bushfire outbreak for NSW would be on the south coast.
But with frontal low pressure systems further north off the NSW south and central coast, the early bushfire season this spring has been further north, on the north coast, the northern tablelands and south-east Qld.
