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

10 5 0
Feb
16

4
Mar
16

7
Apr
16

4
May
16

3
Jun
16

10
Jul
16

7
Aug
16

4
Sep
16

10
Oct
16

1
Nov
16

10
Dec
16

7
Jan
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 remains strong, but its showing a gradual decline. All major international climate models suggest this event will return to neutral by mid-year. The NINO3.4 value for January was +2.1, slightly cooler than the previous month. The Southern Oscillation Index (SOI) showed a significant strengthening deepening to -19.7. Although slightly cooler, sea surface temperatures (SSTs) across the equatorial pacific continue to exhibit the typical pattern of an El Nino, however, the waters around the Maritime Continent continue to be significantly warmer than average. El Nino is typically associated with drier conditions through the eastern and southern states during spring but the breakdown of strong El Nino events has been linked to above average rainfall through some parts of Australia in the first half of the year. After an active phase of the North Australian Monsoon (NAM) in late December, January ended up seeing very much below average rainfall across the tropical north. Most of the southern half of Australia, however, experienced above average rainfall. With easing El Nino conditions across the Pacific, models are suggesting a return to neutral or even above average rainfall across areas of the southern and eastern states. In the short term and as the seas continue to warm up, coastal areas along the eastern seaboard are likely to see a continuation of the increased rainfall due to localised convective activity. Record breaking SSTs across the southern Indian Ocean continue to drive the rainfall outlook for western parts of the country, with extra moisture in the atmosphere likely to bring average to slightly above average rainfall for southern WA and SA. Across northern Australia, below average rainfall is likely during the second half of the Wet Season. This is based on projections of an erratic NAM with weaker and fewer active phases. In the longer term, there is no clear indication of what will happen after this El Nino event fades away by mid-2016. 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. 

Issued 08 Feb 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.