No spring in the step following BOM forecast

BOM seasonal outlook forecasts below average spring rain


Weather
The BOM map on the likelihood of exceeding median rainfall is not pleasant viewing, especially for those in south-eastern and south-western Australia.

The BOM map on the likelihood of exceeding median rainfall is not pleasant viewing, especially for those in south-eastern and south-western Australia.

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Farmers hoping for a change in weather patterns were left disappointed with a BOM forecast predicting below average rain for spring.

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THE BUREAU of Meteorology (BOM) seasonal climate outlook, released late last week, was grim reading for those looking for spring rainfall, especially in south-eastern and south-western Australia.

Parts of south-western Western Australia have less than a 20 per cent chance of exceeding median spring rainfall according to the BOM forecast, while the outlook is only slightly less grim for eastern South Australia and western Victoria, where the prediction is for just a 20-30pc chance of getting rainfall above long-term medians.

Both of the major influencing factors on Australian weather, the El Niño / Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are edging close to thresholds associated with drier than average conditions.

And a climatologist with the BOM has warned that the chances of another climate driver emerging to alleviate the impact, such as the series of cold-front driven rain bands which delivered light, but constant rainfall over areas near the southern coast through August, were low.

The Bureau had a similarly gloomy outlook for much of western Victoria and South Australia for August, but rainfall ended up exceeding averages in a number of regions near the coast, although the rain did not reach far inland.

Robyn Duell, senior climatologist with the BOM, said the August rain was due to the sub-tropical ridge pushing slightly higher than some models had predicted, meaning rain-bearing cold fronts just grazed southern landmass instead of falling over the ocean.

However, she said a one-two punch of an IOD positive and an El Niño was powerful.

“With positive IOD events you tend to see rain through southern areas limited as the cold fronts slip further to the south,” Ms Duell said.

“The El Niño means that tropical moisture sources to the north-east are down as well.”

In drought stricken NSW and Queensland the outlook is not quite so grim.

Areas such as the Darling Downs are rated neutral for rainfall, with a 45-55pc chance of exceeding average spring rainfall, which gives at least some hope of generating sufficient soil moisture for a summer crop planting.

Much of the NSW cropping belt through the Central West and the Liverpool Plains is rated a 35-45pc chance of getting median rainfall, with odds of achieving that mark declining to the south and west of the state.

The likely lack of rain is not the only grim news for grain producers with crops on a knife edge, such as is the case in northern Victoria and drier parts of South Australia.

Ms Duell said the outlook also predicted hotter daytime temperatures, meaning heat stress could be a  factor, while she said the likelihood of more clear days than usual meant frost risk was also higher.

The likelihood of warmer conditions than usual is most pronounced in the north and west of the country.

She said winter across Australia as a whole had been one of the warmest on record.

The ENSO index is currently neutral, however all international models used by the BOM are predicting El Niño thresholds will be reached by the end of spring.

Roughly half the climate models are predicting an IOD positive event.

The 2018 spring outlook is the first end-of-month seasonal outlook produced using the Bureau's upgraded ACCESS-S climate outlook model.

The new model better simulates regional climate patterns, providing more accurate and localised outlooks, using a 60km, rather than 256km grid.

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