12-Month Rainfall Forecast
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Central West 12-month Rainfall Forecast
May
21Jun
21Jul
21Aug
21Sep
21Oct
21Nov
21Dec
21Jan
22Feb
22Mar
22Apr
22
10
50
756776717715Rainfall deciles
10Well above normal8 - 9Above normal4 - 7Near normal2 - 3Below normal1Well below normalIssue Notes
Issued 10 May 2021ENSO status: Neutral. IOD status: Neutral. SAM status: Positive. La Niña has officially ended, with neutral conditions expected until at least the end of winter, therefore having no effect on our climate here in Australia. While La Niña has returned to neutral, the oceans around northern Australia are warmer than normal. This may enhance rainfall during the next month or so, before the oceans return to normal conditions. The Indian Ocean Dipole (IOD) is expected to continue to be neutral at least until early winter. The confidence in the IOD forecast at this time of the year is low, specifically because the models are showing a range of outcomes from mid winter onwards. During winter, much of the Australia is likely to be wetter than normal, apart from far southwestern WA, southern VIC and much of TAS. The warmer than normal oceans may be playing a role in this outlook, potentially feeding moisture into cold fronts sweeping across Australia's snowfields. Therefore a normal to above normal snow season is forecast. Springs rainfall at this stage is forecast to be above normal for much of the Australia, apart from far southwestern WA, parts of southeastern QLD and NSW, southern VIC and much of TAS. The warmer than normal oceans may be playing a role in this outlook, potentially feeding moisture into cold fronts sweeping across Australia's snowfields.
Forecast ExplanationNotes on the concept of deciles
If all the data in a record are ranked from lowest to highest they can then be divided into 100 equal blocks. These blocks are known as percentiles. The values that fall into the lowest 10% range (from 0 to 10%) are said to be in the first decile, those in the group 10+% to 20% are in the second decile, and so on. Those in the group 90+% to the maximum value recorded are in the 10th decile. The 50% value is a special one known as the 'median'. It is noteworthy since there is the same number of records above and below its value.
Deciles have been found to be very useful for analysing rainfall in particular as its distribution is not the normal bell-shape distribution but is skewed towards many low values with only a few high values. The deciles can be described in qualitative terms. A table is provided in the accompanying results.
