The NINO3.4 index is one of several El Niņo/Southern Oscillation (ENSO) indicators based on sea surface temperatures.
NINO3.4 is the average sea surface temperature anomaly in the region bounded by 5°N to 5°S, from 170°W to 120°W. This region has large variability on El Niņo time scales, and is close to the region where changes in local sea-surface temperature are important for shifting the large region of rainfall typically located in the far western Pacific.
An El Niņo or La Niņa event is identified if the 5-month running-average of the NINO3.4 index exceeds +0.4°C for El Niņo or -0.4°C for La Niņa for at least 6 consecutive months.
A series of strong cold fronts which are moving in quick succession over southeastern parts of Australia threaten to bring low level snow over the coming days to parts of Tasmania.
Adelaide has recorded its chilliest July in close to 20 years, with both maximum and minimum temperatures colder than average.
A continuous series of cold fronts and brisk north-westerly winds have contributed to the coldest July in Melbourne in two decades, the Bureau of Meteorology says.