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12-Month Rainfall Forecast

  1. Adelaide 12-month Rainfall Forecast

    Oct
    21
    Nov
    21
    Dec
    21
    Jan
    22
    Feb
    22
    Mar
    22
    Apr
    22
    May
    22
    Jun
    22
    Jul
    22
    Aug
    22
    Sep
    22

    10

    5
    0

    6
    8
    8
    8
    8
    7
    6
    3
    7
    7
    4
    6

    Rainfall deciles

    10
    Well above normal
    8 - 9
    Above normal
    4 - 7
    Near normal
    2 - 3
    Below normal
    1
    Well below normal

    Issue Notes

    Issued 13 Oct 2021

    ENSO status: Neutral, however six of seven models suggest La Niña thresholds will be met again between November and January. IOD status: Negative, neutral levels predicted from late spring. SAM status: Near neutral, forecast to be mostly positive from October to December. The El Niño–Southern Oscillation (ENSO) is currently neutral. However, Over the past few months, sea surface temperatures in the central and eastern equatorial Pacific Ocean have been getting abnormally cool. This oceanic cooling has also been accompanied by a response in the atmosphere, which has included trade winds strengthening over the central and western Pacific Ocean in the last few weeks. Both the atmosphere and the ocean are now showing clear signs of being in a La Niña-like pattern and a number of forecast models suggest that this trend will continue in the months ahead. All seven climate models predict La Nina Thresholds to be met in November, while six of the seven suggest it will last through to January and four toFebruary. La Niña typically brings above average rainfall in northern and eastern Australia. The Indian Ocean Dipole (IOD) is currently weakly negative, however climate models predict the return to neutral phase by late spring. A negative IOD generates above average rain to southern and eastern Australia. As such, average to above average rainfall is predicted across much of the country this winter and the remainder of spring.

    Forecast Explanation

    Notes 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.