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

10 5 0
Jul
15

1
Aug
15

3
Sep
15

2
Oct
15

4
Nov
15

6
Dec
15

8
Jan
16

3
Feb
16

3
Mar
16

8
Apr
16

3
May
16

6

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

Sea Surface temperatures (SSTs) across the central Pacific have continued to exceeded El Nino thresholds. Trade winds in the overlying atmosphere have remained weak, with an El Nino now well established. Most international climate models suggest this El Nino event is likely to continue throughout the winter and spring. The monthly NINO3.4 value continued to warm, ending up at 1.03 degrees in May. The Southern Oscillation Index (SOI) dipping to -13.7 in May. Subsurface temperature anomalies along the equatorial Pacific (top 300m of the water column between the Date Line and 100 degrees west) experienced a dramatic warming during May. This warming was most significant off the coast of South America with a temperature anomaly greater than 4 degrees above average. Warmer than average subsurface waters now extend from the Date Line to the American continent. Despite El Nino, SSTs across Australia remain quite warm along the eastern seaboard. These SSTs are likely to result in increased moisture levels in the atmosphere. As such, long range forecast models are favouring near-to-above average rainfall through eastern of Australia, particularly near the coast during the winter. It is important to remember that winter is the driest season for most of the east. Southern parts of the country, however, are likely to see average-to-below average rainfall over winter. In the longer term, the prospects of an El Nino and a possible Positive Indian Ocean Dipole (IOD) brings a significant risk of average-to-below average rainfall well into the Austral spring across southeastern and eastern Australia. However, the strength of El Nino varies between events and its effects vary year to year. 

Issued 08 Jun 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.