A storm outbreak across south-east Australia is now in its ninth day, boosting March rain totals to near record levels along parts of the slopes and ranges while defying dry predictions for autumn.
The stormy weather is likely to peak during the next 36 hours as thunderstorms spread from southern Queensland to the Victorian coast, including the risk of severe storms in Sydney, Brisbane and Canberra
A Stormy Wednesday
Of all the days during the current spell, Wednesday stands out as the day most likely to have widespread severe weather.
Forecasters look for key ingredients when assessing the risk of severe thunderstorms and all the boxes are ticked on Wednesday from southern inland Queensland, across most of NSW to eastern Victoria :
- The air will be loaded with moisture
- Warm north-westerly winds at the surface will make the atmosphere unstable
- A jet stream will aid updrafts and organise thunderstorms
Canberra can expect storms to arrive from the morning while for Sydney a band of thunderstorms should arrive from the west around the middle of the day, possibly in the form of a squall line.
Squall lines occur when thunderstorms become organised in a near-straight line and often bring damaging wind gusts.
The line should form in the morning across the Central West of NSW before moving east over the Blue Mountains around noon.
The main band of thunderstorms should then reach the Hunter, northern ranges and southern Queensland through the afternoon, including Brisbane.
Thursday south-east Queensland
A cooler, drier southerly airstream will clear storms from NSW by Thursday but the threat of severe weather will continue in south-east Queensland.
Brisbane and surrounding regions could even see supercell storms, the long-lasting rotating thunderstorms capable of producing torrential rain, giant hail and destructive winds.
The band of storms will then shift to central-east Queensland from Friday as the cooler southerlies continue pushing north.
But indications are that humid northerly winds and the threat of thunderstorms will return to south-east Australia early next week.
An unusually long March spell of storms
While March is still within the thunderstorm season it is well past the peak of late spring and early summer.
Sydney, for example, averages less than two thunder days in March, but many regions along the slopes and ranges have already seen several thunder days during the past week.
Orange has recorded eight consecutive days with rain and has tallied more than 160 millimetres this month, more than double the March average.
Tamworth's total has climbed above 170mm, more than triple the average and the city's wettest March in 129 years. Gunnedah's total in excess of 180mm is the highest since 1941.
Warm waters save autumn rains
The current wet spell is going against the grain of the grim autumn forecast of La Niña's demise and a rapid shift to dry weather.
La Niña did conclude as expected but a quick glance at the satellite reveals a country either under a blanket of clouds or spotted with storms, and the forecasts into early April are dominated by rain.
So where is the rain coming from?
Surveying model forecasts for autumn reveals one anomaly which could explain the continued wet weather — sea surface temperatures surrounding Australia are currently warmer than normal, a pattern not picked up by models back in summer.
A similar scenario played out through 2015 when the usual dry weather from a strong El Niño was suppressed by localised warm waters around Australia.
Farmers across the country will be hoping that if an El Niño does develop in 2023, another climate driver is again able to offset the impact.
