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

10 5 0
Aug
15

2
Sep
15

4
Oct
15

2
Nov
15

5
Dec
15

6
Jan
16

6
Feb
16

2
Mar
16

6
Apr
16

2
May
16

5
Jun
16

9

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

An El Nino event continues to dominate the Pacific Ocean Basin. Sea surface temperatures (SSTs) have continue to warm up along the equator, while easterly winds across the far western Pacific have considerably weaken. Most international climate models suggest this El Nino event is likely to continue throughout the winter and spring. The monthly NINO3.4 value for June was 1.3 degrees. The Southern Oscillation Index (SOI) continued to be negative at -12 in June. Subsurface temperature anomalies along the equatorial Pacific (top 300m of the water column between the Date Line and 100 degrees west) continue to warm during June. This warming is most significant off the coast of South America with a temperature anomaly greater than 4 degrees above average. Warmer than average subsurface waters now extend from 150 degrees East to the American continent. During El Niņo, eastern Australia and some parts of southern and central Australia tend to see below-average winter and spring rainfall. El Nino is also associated with above-average daytime temperatures over the southern half of the country during this period. Moreover, the Indian Ocean Dipole (IOD) is currently neutral. However, consensus suggest a positive IOD is likely during the southern spring. A positive IOD is typically associated with reduced winter and spring rainfall over parts of southern and central Australia which is likely to exacerbate the effects of El Nino. As such, rainfall over southern and eastern Australia is likely to trend into average-to-below average throughout winter and spring. Warmer than average coastal waters off the eastern seaboard, however, are likely to enhance the moisture content in the atmosphere bringing average-to-above average rainfall east of the great Dividing Range during July and August. This will be more likely if any East Coast Low does develop during this period. Across the west, warmer than average SSTs over the central Indian Ocean are likely to increase the moisture levels in the atmosphere, leading to an enhanced risk of average-to-above average rainfall for central and southern parts of WA during winter. This is likely to be reversed with the beginning of spring, which could see a decrease in rainfall over the west. 

Issued 08 Jul 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.