12-Month Rainfall Forecast
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Mid North 12-month Rainfall Forecast
Mar
24Apr
24May
24Jun
24Jul
24Aug
24Sep
24Oct
24Nov
24Dec
24Jan
25Feb
25
10
50
854765666987Rainfall deciles
10Well above normal8 - 9Above normal4 - 7Near normal2 - 3Below normal1Well below normalIssue Notes
Issued 20 Mar 2024ENSO status: El Niño, breaking down. IOD status: Neutral. SAM status: Negative, trending slightly positive. The El Niño Southern Oscillation (ENSO) is in an El Niño and is breaking down. All international models indicate neutral conditions should return by late April or early May. The Southern Oscillation Index (SOI) is varying significantly with tropical activity over Australia and the Pacific. Waters in the Coral Sea are far warmer than normal, especially for an El Niño, and are offsetting the effects of this event. El Niño only has a small effect during autumn, typically increasing rainfall over the Nullarbor and SA, but having little effect elsewhere. The Indian Ocean Dipole (IOD) is in a neutral phase. Ocean temperatures are high across most of the Indian Ocean. The IOD index is spiking in response to hot waters near Africa, more-so than the average temperatures near Indonesia and WA. The IOD has little to no effect during autumn. The Southern Annular Mode (SAM) is negative and will slightlyfavour a positive phase during April and May, and possibly into winter. A positive SAM increases easterly winds, increasing rainfall and thunderstorm activity in the east. As we go closer to winter, a positive SAM also reduces cold fronts and rainfall over southern Australia. The reverse occurs with a positive SAM, with more frequent cold fronts crossing the south. Rainfall outlooks are predicting average rainfall for the vast majority of Australia throughout autumn. There are some weak signals that southwest WA could be slightly drier than normal in April, and eastern Qld and northeast NSW could be slightly wetter during May, but otherwise near average.
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.