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

10 5 0
Sep
15

4
Oct
15

2
Nov
15

5
Dec
15

9
Jan
16

3
Feb
16

1
Mar
16

6
Apr
16

1
May
16

3
Jun
16

9
Jul
16

4

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

El Nino continues to dominate the Pacific Ocean Basin. Warming of the sea surface temperatures (SSTs) along the equator continued during July, with westerly wind bursts observed to the west of the Date Line. Most international climate models are now forecasting a strong El Nino, peaking early 2016. The monthly NINO3.4 value for July was 1.6 degrees. The Southern Oscillation Index (SOI) continued to be negative at -15 in July. Warmer than average subsurface waters continue to extend from 150 degrees East to the American continent. During El Niņo, eastern Australia and some parts of southern and central Australia tend to see below-average winter and spring rainfall. However, there is no direct correlation between the strength of an El Nino and its effects on rainfall across the Australian continent. Although it remains within neutral parameters, model consensus suggest a positive Indian Ocean Dipole (IOD) is likely during the southern spring. A positive IOD is typically associated with reduced winter and spring rainfall over parts of southern and central Australia, which is likely to exacerbate the effects of El Nino. In the shorter term, a negative Southern Annular Mode is likely to bring reduced rainfall to central and northern parts of the continent, except for WA's southwest corner and the southern coasts of SA, VIC and most of TAS. In the long term, rainfall over southern and eastern Australia is likely to trend into average-to-below average during spring and early summer. Western Australia and far western parts of South Australia are likely to see above average rainfall due to the warm SSTs over central parts of the Indian Ocean, which is likely to increase the available moisture to any front moving across the west. 

Issued 11 Aug 2015

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.