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

10 5 0
May
14

4
Jun
14

7
Jul
14

5
Aug
14

5
Sep
14

7
Oct
14

3
Nov
14

5
Dec
14

4
Jan
15

4
Feb
15

7
Mar
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

Both the El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are likely to remain neutral through autumn, however there continues to be strong support for the development of an El Nino during the southern hemisphere winter. During the last two months there has been significant warming of subsurface sea temperatures across the central and east-central tropical Pacific, which has persistently been spreading further east across the tropical Pacific. More recently this has led to some warming at the surface of the central tropical Pacific, a trend that is expected to continue and lead to the development of an El Nino. In addition, two strong westerly wind bursts have occurred since the start of the New Year with anomalous low-level westerly winds over the central Pacific persisting during the past weeks, further supporting the trend towards El Nino. Atmospheric indicators are also showing this shift towards El Nino, with Southern Oscillation Index (SOI) values dipping to -13, the lowest 30-day value since March 2010. These values would need to remain firmly negative for several weeks to indicate the atmosphere and ocean are coupling for an El Nino. For the remainder of autumn and start of winter, models indicate that southeastern parts of the nation will experience near-to-slightly above average rainfall totals. During the the seond half of winter and into spring, rainfall totals are expected to hold close to average as the El Nino pattern begins to take shape. While rainfall is expected to be close to average, temperatures are likely to remain above average, which would be expected to result in more rainfall events than snowfall in the Alpine areas. Along the eastern coast of Australia, rainfall totals are expected to be near or above average through autumn and into the start of winter due to a more predominant onshore flow and warm seas along the coastal fringe. In addition, there could be an increased number of East Coast Lows as cold front begin to push further north over the Tasman Sea and interact with the warmer than average waters. Rainfall should then trend near to below average moving into spring with the expectation for the developing El Nino. The chance of El Nino developing is greater than a 50% chance during winter, with around a 40% chance of remaining in a neutral phase and a minimal risk of La Nina. El Nino is often, but not always, associated with below normal rainfall across large parts of southern and inland eastern Australia during the second half of the year. In addition, the Australian wet-season onset is greatly affected by the El Nino-Southern Oscillation. During El Nino years, the onset date tends to be later in the year than normal, which could lead to drier conditions across northern Australia and early heating. For New Zealand, rainfall totals are expected to be near-to-slightly above average across far northeastern parts of the nation during the remainder of autumn and winter due to moist northeasterly flows. For the remainder of the nation, climate models indicate that rainfall totals will be below average during autumn and winter due to anomalously high pressures. 

Issued 07 Apr 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.