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

10 5 0
Mar
15

5
Apr
15

4
May
15

3
Jun
15

9
Jul
15

5
Aug
15

5
Sep
15

4
Oct
15

5
Nov
15

7
Dec
15

6
Jan
16

4
Feb
16

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

The tropical Pacific Ocean has remained in an ENSO-neutral state, following the borderline El Nino conditions that were observed late in 2014. However, there has been a slight warming across the region, mainly over the far western and far eastern parts of the basin. This recent warming, coupled with increasing temperatures in the subsurface are tilting the balance towards a possible El Nino during the second half of 2015. The sea surface temperatures (SSTs) across the equatorial region around the Date Line continue to show the greatest warming anomaly, about 1-2 degrees warmer than the norm. In the eastern equatorial Pacific, cooling was initially observed off the coast off Ecuador in early February. However, the second half of the month saw a considerable amount of warming in this region. The monthly NINO 3.4 value showed no difference, remaining at +0.5 in February. Subsurface temperature anomalies along the equatorial Pacific (top 300m of the water column between the Date Line and 100 West) have also continued to warm during February. This warming has been most significant over the western and central Pacific with a current temperature anomaly greater than 2 degrees above the average. The overlaying atmosphere has remained relatively stable with the Southern Oscillation Index (SOI) hovering just above zero during the second half of February. The monthly SOI value remains at +0.8. Trade winds, however, were weaker than average over the tropical west Pacific during late February with near-average trade winds over the eastern half of the basin. Both El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are expected to remain within neutral values during the austral autumn. Neutral periods indicate that the equatorial Pacific and Indian Oceans are not shifting the odds towards a significantly wet or dry period for Australia, however there are other factors to consider. The ENSO values, despite being neutral, are likely to remain on the warmer side throughout this period with increasing odds of even further/sustained warming during the austral winter. Due to the underlying warmer than average SSTs that exist across the tropical pacific, model consensus suggest increasing odds for an El Nino event later this year. In the absence of strong climate drivers, SSTs and short term atmospheric pressure anomalies are likely to influence rainfall distributions around the nation. During autumn and early winter, climate models indicate that SSTs will remain warmer than average around much of the nation, which will result in increased moisture levels. As a result, long range forecast models are favouring near-to-above average rainfall through eastern and southwestern parts of Australia, particularly near the coast where we find a strong Eastern Australian and Leeuwin Currents advecting warm tropical waters towards the poles. Forecasts are for near-to-below median rainfall through Victoria and South Australia, where intra-seasonal variability of the Southern Annular Mode is likely to keep fronts further south than usual. 

Issued 05 Mar 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.