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

10 5 0
Feb
15

7
Mar
15

4
Apr
15

4
May
15

5
Jun
15

8
Jul
15

7
Aug
15

3
Sep
15

1
Oct
15

2
Nov
15

7
Dec
15

5

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

Oceanic and atmospheric conditions have recently backed away from an El Nino trend, after being close to El Nino thresholds for several weeks. Despite the recent weakening of the indicators, there remains a 50% chance of a weak El Nino eventuating during the next few months. During December 2014, positive sea surface temperature (SST) anomalies decreased across the central and east-central equatorial Pacific, although SSTs still remain above average across much of the equatorial region. The Southern Oscillation Index (SOI) remained slightly negative, but rainfall remained below-average near the Date Line and was above-average over Indonesia, which is uncharacteristic of an El Nino. Overall, the combined atmospheric and oceanic state remains ENSO-neutral. Based on the current observations and output from global climate models, there is an approximately 50% chance of El Nino conditions during the next two months, with ENSO-neutral favoured thereafter. During the end of 2014, the El Nino-like conditions and a delayed onset of the North Australian Monsoon resulted in below average rainfall across large parts of the nation. An active phase of the monsoon developed during the start of January and will contribute the heavy rainfall across central and southern parts of the nation through the remainder of January. With the chance for a fully-fledged El Nino easing and warmer than average seas persisting around much of the continent, rainfall totals are expected to remain near average across southeastern parts of the nation through the remainder of summer and into autumn. Drier conditions are expected through Queensland and parts of Western Australia with a lower amount of tropical cyclone activity expected for the season. At this stage, model guidance is indicating that rainfall totals will trend below average through southeastern parts of the nation during winter. 

Issued 09 Jan 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.