Australia's major climate drivers—the El Niño–Southern
Oscillation (ENSO) and the Indian Ocean Dipole (IOD)—are likely to remain
neutral through winter. When ENSO and the IOD are neutral they typically have
little, if any, largescale influence on Australian rainfall and temperature
patterns.
But even with these big climate drivers doing little to push
our weather one way or another, the next fortnight is likely to be wetter than
average for large parts of south-eastern Australia, including Victoria.
For April, western Victoria could see above average
rainfall.
The long-range outlook for April to June shows slightly increased chances of above average
rainfall for western Victoria, while East Gippsland could see less rainfall
than normal.
Chance of exceeding median rainfall for April to June
There are roughly equal chances that days will be warmer or
cooler than average for April overall. However, the three-month April to June
outlook indicates eastern Victoria is likely to have warmer days than usual.
Parts of northern Victoria are likely to have warmer than
average April nights, and that expands to the whole State (and country) for
April to June.
With our major climate drivers being neutral, there are other
factors are influencing the outlook.
Typically in the autumn after a positive IOD (we had one of
the strongest on record IOD events last year), warmer than average ocean
temperatures in the tropical eastern Indian Ocean bring more northwest cloud-bands
– those long lines of cloud that cross the country from northwest to southeast.
This draws moisture from the tropics right down to Victoria. If this moisture meets
a cold front or low-pressure system, it can trigger off good rainfall,
resulting in wetter than average conditions for Australia's southeast.
Warmer than average oceans around the coastline are also
likely contributing to the warmer than average outlook over Australia.
Australia's temperature and rainfall variability are also
influenced by long term trends in our climate. Australia's climate has warmed
by around 1.4 °C since 1910, and there has been a decline of around 11 per
cent in April–October rainfall in the southeast of Australia since the late
1990s.
The Bureau of Meteorology's climate model includes the
influence of climate change and natural climate drivers like ENSO, IOD, and the
Southern Annular Mode in its outlooks.