Medium Term Climate Outlooks
National Seasonal Rainfall Outlook: probabilities for August to October 2010
Wetter conditions favoured in the northeast
issued 22nd July 2010
The national outlook for total rainfall over the late winter to mid-spring period (August to October), is neutral with the odds favouring neither wetter nor drier conditions across most of the country with the exception of small parts of Victoria, Tasmania and northern NSW.
The pattern of seasonal rainfall odds across Australia is a result of recent warm conditions in both the Indian and the Pacific Oceans, although both of these oceans have cooled over the last few months.
For the August to October period, the chance of exceeding median rainfall is between 40 and 60% in most parts of the country (see map).
Probability of exceeding median rainfall - click on the map for a larger version of the map
This means that for every ten years with ocean patterns like the current, about five August-October periods would be expected to be drier than average over these areas, while about five periods would be wetter.
In a small region of southern Victoria, the chances of a wetter than normal season drop below 40% indicating an increased risk of dry conditions. In contrast, over a small patch in northern NSW the chance of exceeding the seasonal median rainfall is about 60% indicating an increased risk of wet conditions.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During August to October, history shows this effect to be moderately consistent across most of Queensland, the east and north of the NT and the northern inland of NSW. Elsewhere, it is generally weakly consistent, reaching moderate in some areas, including in southeast SA, western and central Victoria (see background information).
Most leading climate models indicate further cooling of the equatorial Pacific during the coming months, with the development of La Niña conditions considered likely to occur during the winter. For routine updates and comprehensive discussion on any developments regarding El Niño and La Niña, please see the ENSO Wrap-Up.
Click here or further detail.
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Short Term Observations
Current Satellite (Bureau of Meteorology)
Synoptic Chart (Bureau of Meteorology)
24 Hour Rainfall observations (Bureau of Meteorology)
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Bureau Of Meteorology:
ENSO Wrap-Up: Pacific Ocean in early stages of a La Niña event
A regular commentary on the El Niño-Southern Oscillation
CURRENT STATUS as at Wednesday 21 July 2010
Tropical Pacific Ocean temperatures continued to cool over the past fortnight, and are now approaching levels typical of a La Niña. Similarly, other ENSO indicators are also at or exceeding La Niña thresholds. As computer models predict the central Pacific will continue to cool over the coming months, it is now highly likely that the Pacific is in the early stages of a La Niña event, and that 2010 will be considered a La Niña year.
Signs of an emerging La Niña event have been apparent in the equatorial Pacific for several months. Pacific Ocean temperatures have cooled steadily throughout the year and are now more than 1°C cooler than average in some areas on the equator.
The Southern Oscillation Index (SOI) has increased in value and is currently around +14, trade winds continue to be stronger than average and cloudiness has remained suppressed over the central Pacific. All of these key indicators are at levels typical of the early stages of a La Niña event.
Source: BOM (Chart Updated Wednesday 2nd June 2010)
WA Dept of Agriculture: Growing Season Outlook
July 2010
Contributors: David Bowran, Fiona Evans, Ian Foster, Phil Goulding, David Stephens
Summary:
A rapid reversal in ocean atmosphere coupling over the last three months now means there is a high chance of a La Nina developing in coming months. However, consistent with changes observed in April-June over the last decade, rain-bearing systems have been weaker than normal over Western Australia. The sea surface temperature gradient to the north and west of WA has reduced, with a warming of water in the central Indian Ocean west of Perth contributing to a dry pattern in the short-term.
A consensus of most climate models is that rainfall is likely to be below normal for winter over most parts of the WA grainbelt. For eastern Australia, better rainfall and crop prospects are indicated and a developing La Nina pattern adds confidence to the rainfall outlook. For northern and eastern areas of the WA wheatbelt low soil moisture reserves and low yield potentials requires a conservative approach to crop inputs for the remainder of the season.
Click here for complete Growing Season Outlook.
Elders Weather Medium Term Outlook (Issue Notes)
Issued 28 Jul 2010
The hemispheric long wave pattern has been relatively slow moving in recent weeks. There are three main troughs. Currently the most significant troughs are near the longitudes of the southwest Indian Ocean, Western Australia, and the southeast Pacific. Summary: Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 9 August to 13 August, 14 August to 18 August, and 30 August to 3 September. Rain events originating in the tropics and moving south are possible about 12 August to 16 August, 23 August to 27 August, and 30 August to 3 September. Over Western Australia the strongest cold fronts should occur about 14 August to 18 August, 20 August to 24 August, and 31 August to 4 September.
For more information click here.
Elders Weather 12 Month Rainfall Forecast
Issued 13 Jul 2010
During June, waters over the eastern Pacific continued cooling and trade winds over the western Pacific strengthened. These factors now indicate a high chance of a La Nina event developing over the coming months. Coupled climate models are indicating that La Nina thresholds could be surpassed before the end of the austral winter. It is considered a strong chance (80%) of La Nina being in place by the summer (December) with just a 20% likelihood of neutral conditions.
Forecasts until October continue to show likely rainfall close to or above median for southeast QLD, and for central and eastern NSW. For northeast/Alpine Victoria and the Snowy Mts rainfall totals are suggestive of more median values.
Spring rainfall forecasts for SA, and for southern and western Victoria remain generally near or below median. Early rainfall forecasts for summer 2010/2011 are generally near or above median for summer-rainfall regions of northern and eastern Australia, driven by the high probability of a La-Nina event. At present the impact of La Nina on VIC and SA is (as usual) expected to be minimal.
For more information click here.
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