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

10 5 0
Dec
14

6
Jan
15

4
Feb
15

5
Mar
15

6
Apr
15

5
May
15

5
Jun
15

8
Jul
15

3
Aug
15

3
Sep
15

5
Oct
15

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

Several features across the tropical Pacific are characteristic of borderline El Nino conditions, but collectively, the combined atmosphere and oceanic state remains ENSO-neutral. There is greater than a 50% chance of an El Nino being declared by the end of 2014, which would continue into early 2015. Indian Ocean Dipole indicators are currently neutral. During October, sea surface temperatures continued to increase across the eastern half of the equatorial Pacific, with the Nino-3.4 averaging +0.6°C during October. In addition, sea temperatures remain elevated at depth across the central Pacific, which is expected to support a continuation of the current near-El Niņo conditions. The Southern Oscillation Index continued to be negative, accompanied by mostly average rainfall near the Date Line and suppressed rainfall over Indonesia. While this is consistent with a developing El Nino, low-level westerly wind anomalies have not been sustained, which is not representative of El Nino and why the pattern has not fully materialised to date. Based on the current observations and output from global climate models, there remains greater than a 50% chance that El Nino will form during 2014. The majority of models suggest that conditions will near-or-just-exceed El Nino thresholds during the next 1-2 months, favouring only a weak event. Australian rainfall and temperature patterns have already shown some El Nino-like impacts, with the country generally warmer and drier than usual over recent months. With El Nino conditions likely to persist into the start of 2015 rainfall totals are expected to remain below median across much of southern and eastern Australia during the summer months. The widespread dry conditions will be particularly evident through the interior. Models indicate that rainfall totals should trend closer to normal during autumn, which is typically when the impact of El Nino begin to diminish. For south-western parts of Australia, rainfall patterns will mainly be influenced by warm waters over the southeastern Indian Ocean with near-to-above median rainfall expected during the remainder of spring and summer. However, it is worth noting that summer is the driest season of the year for southwest WA. 

Issued 09 Nov 2014

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.