Seasonal Climate Outlook Message for May to August 2005

The bottom line

Climate Watch Dave McRae 31/05/05

The SOI has remained relatively stable and as of the 31st May was minus 12.7. Based on the shift in value from minus 10.8 at the end of April, the SOI is now in a 'Consistently Negative' phase.

As expected rainfall probabilities have fallen as a result. Currently there is less than a 30 to 40% chance of getting median rainfall for winter across the southern half of the state. Low rainfall probabilities also extend into parts of central western Queensland, the Central Highlands, Burdekin and the lower half of the peninsular which also have less than a 30 to 40% chance of getting median rainfall for June to August.

For example, there is a 30% chance of getting its winter median rainfall of 105 mm at Warwick, an 18% chance of getting their winter median rainfall of 90 mm, 35 mm and 35mm respectively at Dalby, Quilpie and Townsville, a 15 % chance of getting its winter median rainfall of 100 mm at Kingaroy and a 25% chance of getting its winter median rainfall of 70 mm at Springsure

For the rest of the state there is generally around a 40 to 50% chance of getting median rainfall for winter. It is worth noting that we have entered our normally drier time of year. The latest rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au

Another way of looking at this is that in around 2 to 3 years out of 10 historically (or around one quarter) with the current SOI pattern, Roma has received at least 85 mm over June to August. Therefore in 7 to 8 years out of 10 historically (or around three quarters), Roma has gotten less than 85 mm over June to August.

Because rainfall probabilities and median rainfall levels vary between regions, we recommend referring to Rainman StreamFlow for more specific information. Otherwise call the DPI Call Centre on 13 25 23 or (07) 3404 6999.

The full story

Climate Watch 31/05/05

SOI in Negative Phase

The SOI has remained relatively stable and as of the 31st May was minus 12.7. Based on the shift in value from minus 10.8 at the end of April, the SOI is now in a 'Consistently Negative' phase.

As expected rainfall probabilities have fallen. Currently there is less than a 30 to 40% chance of getting median rainfall for winter across the southern half of the state. Low rainfall probabilities also extend into parts of western Queensland, the Central Highlands, Burdekin and the lower half of the peninsular which also have less than a 30 to 40% chance of getting median rainfall for June to August.

As with any probability based forecast system it is important to consider the opposite aspect. For example, Roma has a 25% chance of getting above its median June to August rainfall of 85 mm. This also means that there is a 75% chance of NOT getting the 85 mm over June to August. Another way of looking at this is that in around 2 to 3 years out of 10 historically (or around one quarter) with the current SOI pattern, Roma has received at least 85 mm over June to August. Therefore in 7 to 8 years out of 10 historically (or around three quarters), Roma has gotten less than 85 mm over June to August.

When looking at rainfall probabilities for your area it may make it easier to think of them in these terms:

1. Probabilities above 80% highlight a high chance 2. Probabilities above 60% highlight an above average chance 3. Probabilities below 40% highlight a below average chance 4. Probabilities below 20% have a low chance.

Many people like to follow the relationship between the SOI and rainfall patterns in more detail. To do that, have a look at what happened in your area over June to August in the following years; 1997, 1995, 1994, 1993, 1991, 1987, 1977, 1969, 1967, 1951, 1946, 1941, 1940, 1914, 1912, 1905 and 1900 and compare the rainfall recorded with your 'normal' rainfall for June to August.

Information on what rainfall patterns where like for June to August in those years can be found at www.longpaddock.qld.gov.au or in Australian Rainman.

Frost occurs with a combination of still cold air, clear skies and a dry atmosphere. In the Australian sub tropics, these conditions can be usually found when a high-pressure system is approaching or passing in winter. The local occurrence of frost is dependant on many factors including the terrain, soil type and plant cover. For example, frosts are more common in the bottom of valleys and hollows because cold and dense air travels down slopes. Dark soils are more prone to frosts than lighter coloured soils as they radiate heat at night more rapidly.

A 'Consistently Negative' SOI phase at the end of May (as is the case this year) generally increases the chance of a later than normal finish to the severe frost season and may also increase the number of frosts across Queensland.

Similar to rainfall probabilities across Queensland, for the rest of Australia there is generally less than a 50% chance of getting above median rainfall for June to August.

It is worth noting that this doesn't mean there will be no rainfall at all for the 3-month period for those areas with low rainfall probabilities. What it does means though, is that rainfall recorded for June through to the end of August in the affected areas will, more likely than not, be below average for this time of year.

There are a number of 'warning signs' that suggest the development of an El Niño in 2005 is a possibility. According to the Bureau of Meteorology El Niño 'Wrap-Up' the chance of an El Niño this year is around double what may normally be expected.

This is not a guarantee that a classic El Niño SST pattern will develop. There is though, an increasing likelihood that a 'borderline El Niño' SST pattern may develop which would be somewhat similar to what was experienced over the last 12 months.

So our policy remains to recommend a cautious approach when considering the longer-term outlook this year.

Last updated: 30 May 2005

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