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

10 5 0
Nov
14

4
Dec
14

3
Jan
15

3
Feb
15

6
Mar
15

4
Apr
15

3
May
15

7
Jun
15

8
Jul
15

3
Aug
15

5
Sep
15

7

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

Over the past month, warm subsurface sea temperatures persisted in the central tropical Pacific, while atmospheric ENSO indicators have remained just below El Nino thresholds. There is still greater than a 50% chance of an El Nino being declared in 2014, most likely during late spring or summer. Indian Ocean Dipole indicators have continued to weaken and have fallen back into a neutral state. During September 2014, above-average sea surface temperatures (SSTs) continued across much of the equatorial Pacific. Most of the Nino indices continued to warm during the month, with the Nino-3.4 averaging +0.45C during September. In addition, the Southern Oscillation Index (SOI) has remained negative since the start of July, falling below the El Nino threshold during the past few weeks. Based on the current observations and output from global climate models, there remains greater than a 60% chance that El Nino will form during 2014. The consensus of models suggest that conditions will near-or-just-exceed El Nino thresholds during the late spring or early summer, favouring only a weak event. The Indian Ocean Dipole (IOD) has continued to weaken with waters to the north of Australia returning to near-average temperatures. A negative IOD helped to bring modest winter/early spring rain to western and southern areas of the country, however impacts from the IOD are expected to be minimal in the months ahead. As El Nino conditions begin to exert more influence and higher pressure becomes established across southern Australia, rainfall totals are expected to trend below median across much of southern and southeastern Australia and persist into summer. The widespread dry conditions will be particularly evident through the interior during late spring and into summer. Models are indicating that rainfall totals will hold closer to median through eastern parts of the nation during summer, which is mainly being influenced by the anomalously warm waters of the Tasman Sea. However, due to the influence of El Nino conditions, it is expected that rainfall totals will favour slightly below median values. For south-western parts of Australia, the IOD will have reduced influence on rainfall patterns during the remainder of spring and summer as it continues to decay. Rainfall patterns in this region 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 07 Oct 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.