- WEATHER
Australia
- National
- New South Wales
- Victoria
- Queensland
- Western Australia
- South Australia
- Tasmania
- ACT
- Northern Territory
Long Range Forecasts
- WARNINGS
- RADAR
- SATELLITE
- MAPS & CHARTS
- LONG RANGE
Long Range Forecasts
- CLIMATE
Climate Indicators
- NEWS
Central West 12-month Rainfall Forecast
10
5
0
| 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: La Niņa Watch.
IOD status: Neutral.
SAM status: Neutral. Favouring negative.
The El Niņo Southern Oscillation (ENSO) is in a La Niņa Watch, meaning there is approximately a 50% chance of a La Niņa developing this year. Overall, models are now starting to look more like La Niņa, with more widespread ocean cooling occurring in the South Pacific, and the 30-day SOI now above +7. While these are good signs that La Nina is starting to develop, a declaration would likely happen no earlier than November, meaning this is more likely to be a late and weaker event if it does eventuate. A La Niņa typically increases rainfall over northern and southeastern Australia during spring, but has little effect for southwestern WA.
The Indian Ocean Dipole (IOD) is in a neutral phase and is now unlikely to develop into either phase this spring. Conditions are closer to a positive IOD than to a negative phase, so there may be some minor reductions in the frequency of northwest cloudbands impacting Australia. A neutral IOD tends to bring a small increase in spring rainfall for southwest WA, but has little effect elsewhere.
The Southern Annular Mode (SAM) is now neutral, having recovered from the initial sudden Stratospheric Warming (SW) event over Antarctica in mid-July. However, another SW event is occurring in mid September that may further dampen the polar vortex. These events increase the chances of negative SAM events during September and October. A negative SAM increases the frequency of cold fronts. During spring, this increases rainfall over western Tas and southern Vic, but decreases rainfall over eastern Australia.
Rainfall outlooks are showing close to average for most of the country during September and October, with a higher chance of above average rainfall for northern and eastern Australia from November. Models are also hinting that rainfall is more likely to arrive in the form of showers and thunderstorms, rather than broad rainbands, meaning rainfall in practice will likely be hit-and-miss for most of Australia this spring.
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.
Enter a postcode or town name for local weather, or text to search the site. » advanced search
Bitter wintry chill returning this weekend
12:22 AEST A two-pronged burst of cold weather is heading the way of southeastern Australia, bringing the sort of chill that was largely missing during Australia's warmest August on record.
Help with Farmonline Weather
