" Adelaide long range forecast - 12 month rainfall forecast
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Adelaide 12-month rainfall forecast

10 5 0
May
16

2
Jun
16

10
Jul
16

3
Aug
16

3
Sep
16

9
Oct
16

2
Nov
16

9
Dec
16

6
Jan
17

2
Feb
17

1
Mar
17

8

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

Adelaide district forecast
Adelaide 28-day rainfall forecast
Issue Notes

The 2015/2016 El Nino continues to weaken and is expected to return to neutral by late autumn or early winter. Through the remainder of autumn and winter, the weakening El Nino and well-above-average-to-record-warm seas around Australia will have the greatest influence on the Australian climate. The Nino3.4 value dropped steadily during March, with an average of +1.64 for the month, the lowest monthly value since July 2016. The latest 30-day Southern Oscillation Index (SOI) is −3.4 (April 3rd), significantly lower than values three weeks ago (−21.5 on 13 March) and below the El Nino threshold. Sea surface temperatures around Australia have been uncharacteristically warm for what is normally seen during an El Nino event. Background warming, a lack of rain and weakened winds across northern Australia contributed to the significantly higher sea-surface temperatures around the nation. Global climate models indicate seas surrounding much of Australia will remain warm into winter and are likely to have a significant influence on rainfall and temperatures. During the remainder of autumn and into winter, the warm waters in the Indian Ocean are expected to influence above average rainfall across parts of Western Australia and into central and southern Australia. Near-to-below average rainfall is favoured for southeastern Australia during the next few months, including Tasmania. While warm waters off the east coast are expected to lead to above average totals through eastern parts of NSW and QLD. During winter, increased seasonal frontal activity across southern Australia, combined with warmer than normal seas, should influence near-to-above average rainfall across much of southern and southeastern Australia. For Tasmania, winter rainfall is expected to be near average overall, potentially slightly above for the West Coast. Beyond winter 2016, there are equal chances for neutral or La Nina conditions with another El Nino unlikely. Out of the past 26 El Ninos: 10 went straight into La Nina (leading to increased rainfall odds), 13 went into neutral and only 3 went back into an El Nino. Currently, some models indicate a negative Indian Ocean Dipole (IOD) later in winter is possible, but the likelihood has decreased from last month. Negative IODs tend to bring above average rainfall and cooler daytime temperatures later in the year. 

Issued 07 Apr 2016

Forecast    Current Conditions    Synoptic Chart    Satellite    Radar   

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.