Meteorologist Alison Osbourne from Sky News Weather noted that an unstable and humid environment is contributing to the thunderstorms across the region.

A cool change is moving through Western Australia, expected to reach South Australia by the evening of January 14, bringing further thunderstorms.

Hailstones as large as tennis and golf balls were reported in Queensland, particularly in Stanthorpe, highlighting the severity of the weather.

Severe thunderstorms are anticipated across various regions, particularly in eastern New South Wales, following a series of storms that began on January 13.

On January 15, Sydney is expected to reach a high of 31°C with possible storms, while Melbourne will see temperatures around 28°C accompanied by showers.

Heavy rainfall over the weekend has already led to flash flooding and reports of large hailstones along the Queensland/New South Wales border.

The recent heavy rainfall has saturated the ground, increasing the risk of flash flooding and rising river levels due to additional precipitation.

Affected states include Queensland, Victoria, New South Wales, the Australian Capital Territory, and Tasmania, with wind gusts predicted to exceed 100 km/h.

The Bureau of Meteorology has issued warnings about potential damage to power infrastructure, which could result in blackouts.

Residents in affected areas are advised to avoid downed power lines, stay clear of creeks and storm drains, and refrain from entering floodwaters.

Individuals should prepare for possible road closures and structural damage as a result of the storms.

Residents are encouraged to stay informed by checking bom.gov.au for ongoing severe weather updates.