On 27 November 2011, heavy rainfall occurred in the northern inland areas of New South Wales. Flood warnings were issued for the Macleay, Severn, Macintyre, Gwydir, Mehi, Namoi and Peel Rivers.

New South Wales State Emergency Service volunteers prepared Wee Waa with food and emergency supplies, with predictions that the swollen Namoi River would isolate the town for some days. The rising waters made the roads in Wee Waa inaccessible to all but four-wheel drive vehicles. Water levels exceeded 6 m around 9:00 am on 27 November, before reaching 7 m on 29 November with major flooding.

Approximately 300 properties were isolated in Moree and the town was cut in two after rising waters forced the closure of the local bridge. More properties were cut off in Gunnedah and the village of Garah, as waters in the Namoi, Gwydir, Peel and Mehi Rivers continued to rise. One person drowned after being pulled into a storm water drain in Bingara, near Inverell.

As the flood waters subsided and moved downstream, the Department of Primary Industries were able to assess the flood damage. Hundreds of livestock, mainly sheep, died with most of the losses occurring between Garah and Weemelah.

It was estimated that approximately $52 million in flood damage occurred to the cotton industry in the Gwydir Valley. The local growers' association says initial estimates were based on around 18,000 hectares, with up to 30 per cent of the dryland crop and five per cent of irrigated crop being damaged.

On 1 December 2011, the New South Wales Government gave natural disaster declarations to Moree Plains, Inverell, Armidale, Gunnedah, Narrabri, Gwydir, Muswellbrook, Liverpool Plains, Tamworth and the Upper Hunter Shire Councils.