Medium Term Climate Outlooks
National Seasonal Rainfall Outlook: probabilities for Autumn 2010
Autumn rainfall odds neutral, except in WA
issued 24th February 2010
The national outlook for total autumn rainfall (March to May), shows odds generally close to 50:50 across much of the country, except in WA and a small part of SA. In WA, below average falls are more likely in the southwest, whereas a wetter season is indicated in northwestern and central areas as well as in small part of SA to the north of Spencer Gulf.
The pattern of seasonal rainfall odds across Australia has been produced using recent Pacific and Indian Ocean temperature patterns; the tropical regions of both oceans have been generally warmer than normal, with the notable exception of northern Australian waters.
The chances of exceeding the median rainfall for March to May are between 30 and 40% over southwest Western Australia (see map). This means that for every ten years with ocean patterns like the current, about six or seven autumns are expected to be drier than average across this part of WA, while about three or four periods are wetter.
Contrasting this, the chances are between 60 and 70% for above average autumn falls in a band stretching from the northwest to the interior of WA, as well as in a region of SA to the north of Spencer Gulf.
Across the rest (and most) of the country, the chances of exceeding the median March to May rainfall are between 40 and 60%, meaning that above average falls are about as equally likely as below average falls.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During autumn, history shows the effect to be moderately consistent across much of the west and the north of the country. Elsewhere the effect is only weakly or very weakly consistent (see background information).
A declining El Niño event exists across the Pacific Basin, with most leading climate models indicating further cooling and a return to a neutral (near-average Pacific temperatures) pattern during the next three to six months. The SOI is approximately −21 for the 30 days ending 21 February. For routine updates and comprehensive discussion on any developments regarding El Niño or La Niña, please see the ENSO Wrap-Up.
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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
A regular commentary on the El Niño-Southern Oscillation
CURRENT STATUS as at 3rd March 2010
Summary: El Niño decay temporarily stalls.
Central Pacific Ocean temperatures have warmed slightly during the last fortnight, slowing the decay of the current El Niño event. A weakening of the trade winds over the western and central Pacific during February triggered not only the recent small warming of the Pacific, but was also related to an increase in cloudiness and tropical cyclone activity in the central Pacific. In recent days, trade winds near the equator have started to return towards near-normal strength and the SOI has rebounded by increasing in value after falling in February.
Computer models are predicting that Pacific Ocean temperatures will continue to cool, returning to neutral levels by the southern hemisphere winter. Typically, autumn is a transitional period for the El Niño-Southern Oscillation (ENSO), and the model forecasts suggest that the decay of the El Niño event is likely to follow the usual pattern.
Recent heavy rainfall over Australia appears fairly typical of past El Niño breakdowns. January 2007, February 2003, April 1998, January 1995, March 1983 and February 1973 all produced good rainfalls over parts of northern and eastern Australia on the back of an El Niño event.
The Indian Ocean Dipole (IOD) is currently neutral and is forecast to remain so through autumn.
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 In Brief
- Central Pacific sea surface temperatures have warmed slightly during the last fortnight, slowing the decay of the current El El Niño event.
- The sub-surface water of the tropical Pacific remains warmer than the long-term average.
- The SOI has increased during the last week after falling rapidly during February. The latest approximate 30-day value of the SOI is −16.
- Trade winds are close to normal across most of the Pacific.
- Cloudiness near the date-line remains above average.
- Most international computer models are predicting a return to neutral conditions by the end of the southern hemisphere autumn.
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Source: BOM (chart updated 2nd Feb 2010)
WA Dept of Agriculture: Growing Season Outlook
February 2010
Contributors: David Bowran, Fiona Evans, Ian Foster, Phil Goulding, David Stephens
Summary:
Moderate El Nino conditions have weakened over the last month in the central and eastern Pacific in
January. However, warm sub-surface water should keep El Nino conditions in place in coming months.
Over eastern Australia heavy rains have been related to warmer than normal SST around most of the
country and a trend towards below normal sea level pressure.
The ESS analogue years suggest that there is a high chance that El Nino conditions should gradually
weaken back to neutral conditions (1958, 1977, 1992 and 2003) and a low chance that El Nino conditions
will persist (1941). The median rainfall map for May-October for these years would be indicative of an
average to above average outlook as being most likely for southern grain growing areas in Western and
eastern Australia. Average to below average rainfall is likely for north-eastern Australia. Confidence in this
outlook is spatially related to new skill maps produced for historical ESS forecasts.
Click here for complete Growing Season Outlook.
Elders Weather Medium Term Outlook (Issue Notes)
Issued 3rd Mar 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 16 March to 20 March, 25 March to 29 March, and 29 March to 2 April. Rain events originating in the tropics and moving south are possible about 19 March to 23 March, 26 March to 30 March, and 1 April to 5 April. Over Western Australia the strongest cold fronts should occur about 20 March to 24 March, 28 March to 1 April, and 1 April to 5 April.
For more information click here.
Elders Weather 12 Month Rainfall Forecast
Issued 8th Feb 2010
The El-Nino state of the Ocean-Atmosphere system over the Pacific continued during January. Atmosphere and ocean observations and coupled climate model forecasts indicate the El Nino peaked during January, and that it is highly likely to weaken significantly during the austral autumn as previously expected. Possible ENSO outcomes for winter and spring of 2010 are split almost evenly between neutral and La Nina-type conditions.
The Indian Ocean Dipole continues to be in a neutral phase. SST's continue to be anomalously warm across the basin. At this stage a positive IOD event during the austral winter and spring appears unlikely. Over the Southern Ocean the Southern Annular Mode continues to be in either a neutral or negative phase.
The warm Pacific conditions will mean a trade winds will be lighter and thus less moisture influx over eastern Australia. The rainfall outlook until the end of autumn is for below average totals across east and south QLD, all of NSW, and northern VIC.
The forecast for the monsoon-affected regions of WA and the NT until the end of February is generally close to median, dropping below median during March and April.
The early autumn, winter and spring outlook for southwestern WA and TAS is for generally close to, or above median rainfall. This outlook is primarily driven by Indian Ocean temperatures.
The early autumn, winter and spring outlook for VIC and NSW is generally close to median.
For more information click here.
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