Northern NSW should see above-average rainfall over the next few months (with a potential for increased flooding), now that the Bureau of Meteorology (BOM) has upgraded its La Nina alert status to 'active'.
The change in status means that recent changes in ocean temperatures and weather patterns over the Pacific are now likely to remain until at least the end of the year.
BOM said La Nina events often form in autumn or winter, then decay in late summer. The greatest impact normally occurs during the spring and early summer period.
The three month outlook for Armidale looks good with a 100 percent chance of at least 150 mls of rain during that period, and a 76 percent chance of at least 250 mls.
The chances are very likely for rainfall levels above the median average of 263 mls from October to December according to BOM data.
La Nina events normally last for around a year, however they can be shorter, or much longer.
La Nina typically results in above-average spring rainfall for Australia, particularly across eastern, central and northern regions. It can also mean cooler days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north.
The last La Nina event occurred from 2010-2012 and resulted in one of Australia's wettest two-year periods on record. Widespread flooding occurred in many parts of Australia associated with the record rainfalls.
Tropical cyclone activity in the 2010-2011 season was near normal. However, five of the tropical cyclones during 2010-11 were in the severe category, which is above average, including Tropical Cyclone Yasi, which caused widespread damage to far north Queensland.
The impacts of La Nina can vary significantly between events. It is likely this year will not see the same intensity as the 2010-11 La Nina event, but is still likely to be of moderate strength.
Watch this La Nina explainer from the bureau...