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Jasminum nudiflorum
As its name suggests, in the Northern Hemisphere winter jasmine flowers from November to March. The solitary flowers, often appearing on the bare stems (hence the Latin nudiflorum, literally "naked flower") have six petals and are bright yellow, or white, about 1 cm across, appearing in the leaf axils. It likes full sun or partial shade and is hardy.
In an urban neighborhood
A belated thanks greenskydesigns! Thanks for your suggestion, too, April, but I think it is the jasmine.