Warmer winter days for south of both NT and Qld
The northern Australian outlook for maximum temperatures averaged over
winter (June to August) shows warmer than normal days are
favoured over the southern halves of both the NT and Queensland.
The pattern of seasonal temperature odds across northern Australia is a result
of recent warm conditions in the Indian Ocean and an increasing level
of warmth in the Pacific.
The chance that the average winter maximum temperature will exceed the
long-term median maximum temperature is above 60% across the southern halves of both the
NT and Queensland, decreasing to 50 to 60% across the remainder of the
This means that for every ten years with ocean patterns like the current, about six
years would be expected to be warmer than average during winter
over southern regions of northern Australia, while about four would be
expected to be cooler.
Outlook confidence is related to how consistently the Pacific and Indian
Oceans affect Australian temperatures. During winter, history shows this
effect on maximum temperatures to be moderately consistent much of the NT
and Queensland (see background information).
The outlook for winter mean minimum temperatures shows a 60 to 65%
chance of a seasonal average above the long-term median minimum temperature over
most of Queensland's southern half. In remaining areas of northern
Australia, the probabilities are in the 50 to 60% range.
History shows the oceans' effect on minimum temperatures in winter to be
moderately consistent over the NT and Queensland.
The Bureau's seasonal outlooks are general statements about the probability
or risk of wetter or drier than average weather over a three-month period.
The outlooks are based on the statistics of chance (the odds)
taken from Australian rainfall/temperatures
and sea surface temperature records for the tropical Pacific and Indian Oceans.
They are not, however, categorical predictions about future rainfall,
and they are not about rainfall within individual months
of the three-month outlook period.
The temperature outlooks are for the average maximum and minimum temperatures
for the entire three-month outlook period.
Information about whether individual days or weeks may be
unusually hot or cold, is unavailable.
This outlook is a summary.
More detail is available from the contact people or from SILO
(Seasonal Climate Outlook Products).
Probability outlooks should not be used as if they were categorical forecasts.
More on probabilities is contained in the booklet
The Seasonal Climate Outlook - What it is and how to use it,
available from the National Climate Centre.
These outlooks should be used as a tool in risk management
and decision making.
The benefits accrue from long-term use, say over 10 years.
At any given time, the probabilities may seem inaccurate,
but taken over several years, the advantages of taking account
of the risks should outweigh the disadvantages.
For more information on the use of probabilities,
farmers could contact their local departments of agriculture or primary industry.
Model Consistency and Outlook Confidence:
Strong consistency means that tests of the model on historical
data show a high correlation between the most likely
outlook category (above/below median)
and the verifying observation (above/below median). In this
situation relatively high confidence can be placed in the
Low consistency means the historical relationship, and
therefore outlook confidence, is weak.
In the places and seasons where the outlooks are most skilful,
the category of the eventual outcome (above or below median)
is consistent with the category favoured in the outlook
about 75% of the time.
In the least skilful areas,
the outlooks perform no better than random chance or guessing.
The rainfall outlooks perform best in eastern and
northern Australia between July and January,
but are less useful in autumn and in the west of the continent.
The skill at predicting seasonal maximum temperature peaks in
early winter and drops off marginally during the second half of the year.
The lowest point in skill occurs in early autumn.
The skill at predicting seasonal minimum temperature peaks in
late autumn and again in mid-spring.
There are also two distinct periods when the skill is lowest
- namely late summer and mid-winter.
However, it must always be remembered that the outlooks
are statements of chance or risk.
For example, if you were told there was a 50:50 chance
of a horse winning a race but it ran second,
the original assessment of a 50:50 chance could still have been correct.
The Southern Oscillation Index (SOI) is calculated using the
barometric pressure difference between Tahiti and Darwin.
The SOI is one indicator of the stage of El Niño or La Niña
events in the tropical Pacific Ocean.
It is best considered in conjunction with sea-surface temperatures,
which form the basis of the outlooks.
A moderate to strongly negative SOI (persistently below 10) is
usually characteristic of El Niño, which is often associated with below
average rainfall over eastern Australia, and a weaker than normal monsoon
in the north. A moderate to strongly positive SOI (persistently above +10)
is usually characteristic of La Niña, which is often associated with
above average rainfall over parts of tropical and eastern Australia,
and an earlier than normal start to the northern monsoon season.
The Australian impacts of 25 El Niño events since 1900 are summarized
on the Bureau's web site
(El Niño - Detailed Australian Analysis).