" Adelaide long range forecast - 12 month rainfall forecast
Other Elders Sites About

Adelaide 12-month rainfall forecast

10 5 0
Jun
16

10
Jul
16

1
Aug
16

3
Sep
16

6
Oct
16

2
Nov
16

10
Dec
16

7
Jan
17

1
Feb
17

2
Mar
17

8
Apr
17

3

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 has continued on its weakening trend 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 further to +1.18 in April, the lowest monthly value since July 2016. The monthly Southern Oscillation Index (SOI) for April was -22, significantly stronger than previous months. The April monthly SOI was significantly influenced by the continuation of a high pressure ridge over the Top End and tropical depressions close to Tahiti. Sea surface temperatures around Australia continue to be uncharacteristically warm. However, we have seen a significant cooling off the west coast of WA. Global climate models indicate seas surrounding northern and eastern Australia will remain warm into winter and are likely to have a significant influence on rainfall and temperatures. Over the coming weeks and months, frontal activity across southern Australia is likely to increase, as is typical for this time of year. This combined with warmer than normal seas (particularly a near-record breaking hot Indian Ocean), should bring near-to-above average rainfall across much of central, southern and eastern Australia. Over recent weeks, most international models have increased the risk of not only a La Nina but also a Negative Indian Ocean Dipole (IOD) developing later in winter and spring. La Nina tends to bring above average rainfall and cooler daytime temperatures later in winter and spring with an negative IOD likely to enhance these. 

Issued 06 May 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.