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

10 5 0
Oct
14

3
Nov
14

4
Dec
14

3
Jan
15

4
Feb
15

6
Mar
15

7
Apr
15

1
May
15

9
Jun
15

8
Jul
15

4
Aug
15

3

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, subsurface sea temperatures have warmed in the central tropical Pacific, while atmospheric ENSO indicators have remained neutral. There is still greater than a 50% chance of an El Nino forming in 2014, however due to the current state of the atmosphere, any event is considered unlikely to be strong. Indian Ocean Dipole indicators have remained negative during the past month, but show signs of weakening. During August 2014, above-average sea surface temperatures (SST) continued across much of the equatorial Pacific. Most of the Nino indices warmed during the month with the Nino-3.4 increasing to +0.4C, up from +0.2C in July. In addition to above average sea surface temperatures, subsurface sea temperatures also increased in the central and east-central Pacific, a result of weak westerly wind anomalies during July and early August. A late season El Nino remains possible if these warmer waters rise to the surface and then affect atmospheric circulation. 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 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) remained negative during August, however has begun to weaken. This helped to bring the recent rain to inland and southern areas of the country. The majority of climate models indicate that the IOD will return to neutral conditions during spring. As the negative phase of the IOD continues to decay and El Nino conditions begin to exert more influence, rainfall totals are expected to trend below to well below median across eastern and southern Australia. The widespread dry conditions will be particularly evident through the eastern and southern interior during late spring and early summer. Models favour a return to near median rainfall for the nation's southeast during the start of 2014, where there is a lower correlation between El Nino and rainfall during summer. Much of eastern Australia is expected to continue seeing near-to-below median rainfall during the start of the New Year. For south-western parts of Australia, the IOD will have reduced influence on rainfall patterns during spring and summer as the negative phase 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 spring and summer. However, it is worth noting that summer is the driest season of the year for southwest WA. 

Issued 12 Sep 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.