I came across the phrase in the following sentence.
The guy who said it is a Kansai speaker. I'm not sure if the phrase is related to the dialect.
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This is western Japan dialect which is equivalent to だなあ in standard Japanese.
It's a part of Kansai dialect in the broader sense, but I think this のう is not very common in typical Kansai-ben spoken in Osaka. AFAIK It's mainly used in Chugoku/Shioku, which is located further west from Osaka.