Wide Bay & Burnett 12-month Rainfall Forecast

10 5 0

No forecast available for this district.

Rainfall deciles
10	Well above normal
8-9	Above normal
4-7	Near normal
2-3	Below normal
1	Well below normal

Issue Notes

ENSO status: Inactive/Neutral. El Niño ended.
IOD status: Neutral, becoming strongly positive.
SAM status: Leading to neutral and returning positive.

The El Niño Southern Oscillation (ENSO) is presently in an inactive phase, for the first time since August 2021. Ocean cooling continues over the eastern Pacific Ocean as sea surface temperatures approach near-normal conditions. Warmer than normal waters are present across the western Pacific Ocean, including the Coral Sea with added moisture and humidity to influence weather conditions in the eastern regions of Australia. The atmosphere continues to be firmly neutral after weakening early in the year with 3 out of 7 global models forecasting a La Niña to develop this coming winter season. A neutral ENSO typically has no significant impact on Australian rainfall during winter.

The Indian Ocean Dipole (IOD) is in a neutral phase, although record-high ocean temperatures across the northwest Indian Ocean have the IOD index just tipping into a positive threshold value. Persistent southeasterly winds over the eastern Indian Ocean during the previous month are forecast to ease with below-average wind speeds to develop off northwest Australia and the eastern Indian Ocean during the winter season. All international models are suggesting the IOD will strengthen into a strong positive phase over the next 2-3 months, with significant upwelling to start near Indonesia possibly following May. A positive IOD reduces the number of northwest cloudbands that cross Australia during winter and spring, thus reducing rainfall across central and southeastern parts of Australia.

The Southern Annular Mode (SAM) is currently positive (mid-April) with the outlook favouring a neutral phase forecast in May and then the likelihood of returning to a positive phase during winter. A positive SAM increases easterly winds, increasing rainfall and thunderstorm activity in the east. A positive SAM also reduces the impact of cold fronts and decreases the rainfall over southern Australia.

Rainfall outlooks are showing above-average rainfall over winter for WA and central and northern SA, and eastern regions of QLD and NSW. Conversely, below-average rainfall is expected for western TAS, southern SA, and most of VIC.

Issued Apr 23

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.

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Rainfall to soak some parched areas of WA

13:00 AEST Rain could finally fall over parts of southwestern WA over the next week, wetting areas that have barely seen any rain for months. This rainfall will be caused by a low pressure trough extending from the Kimberley down to southwestern WA from late Thursday, with a low pressure system developing within it early to mid-next week. The images below shows that widespread rainfall of between 15 to 30mm is forecast in the week across western and southern WA, with isolated falls of between 40 to 60mm in the Gascoyne and Goldfields districts. Image: Accumulated rainfall to 8pm AWST on Thursday, May 2, according to Access (top) and ECMWF (bottom) You can see there is still some uncertainty about where and how much rainfall will fall in these areas late this week and early next week, with one model placing rain over Perth and the other predicting it will completely miss the city altogether. The heaviest rainfall days are likely to be Friday and mid next week when the low pressure system develops.