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

10 5 0
Dec
16

6
Jan
17

4
Feb
17

5
Mar
17

4
Apr
17

1
May
17

6
Jun
17

8
Jul
17

3
Aug
17

4
Sep
17

2
Oct
17

2

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

ENSO status: Neutral. Indian Ocean Dipole (IOD): Negative but weakening. Sea surface temperatures (SSTs) remain within neutral ENSO boundaries. Atmospheric indicators like trade winds and cloudiness near the Dateline, however, are exhibiting La Nina-like characteristics. The Nino3.4 value remained on the cool side of neutral at -0.5 in October. The Southern Oscillation Index (SOI) recorded a value of -4.3 during the same month, also within neutral. The weekly Dipole Mode Index (DMI) continued to exhibit negative values in late October, at -0.6. Current climate model consensus suggests conditions will remain on La Nina-side of neutral with only one in eight international models indicating the development of a fully fledged la Nina towards the end of 2016. The IOD on the other hand, is likely to return to neutral by the end of November/early December. The tail end of the negative IOD that has affected Australia since winter and the warm SSTs across northwestern Australia are likely to maintain average-to-above average rainfall across the western half of the country (more so over the northwest). However, its weakening was evident in October with patchy rainfall across the interior. A possible earlier onset of the North Australian Monsoon (NAM) are also favoring wetter outlook for parts of the north in the coming months. Across the eastern states, neutral ENSO conditions are likely to bring average rainfall during the end of spring and early summer. However, being on the La Nina-side of neutral, we could see some erratic strengthening of the trade winds in the Pacific, which in turn could bring above average rainfall to the east. The seasonal warming of the seas surrounding Australia towards the end of summer could bring increased chances of wetter conditions to the eastern state towards the end of summer/early spring. 

Issued 10 Nov 2016

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.