Black nor'easter

A black nor'easter is a persistent and potentially violent north-easterly storm that occurs on the east coast of Australia, particularly from southeastern Queensland to southern New South Wales, usually between late spring and early autumn, about two days a year (or more, depending on the intensity).^[1]

Developing offshore as a deep coastal trough, the storm is heralded by the rapid build-up of dense black cloud that brings heavy rainfall and strong northeasterly winds along the east coast of Australia. A black nor'easter can be a combination of surface troughs, onshore flow, and a low.^[1] The storm system may cool down warm days due to the persistent blanket of thick moisture-rich clouds.^[2]

Although not convection-driven, the north-east wind field leading warm moist tropical air to the subtropics and mid-latitudes can combine with a higher level cut off low from the Southern Ocean. Black nor'easters were first recorded during the 19th century and were so-named because the affiliated darkness (of the moisture-loaded clouds) can transform the day to as dark as twilight.^[3]