Is the AF cardigan sweater authorized as an outergarment for outdoor wear?

Yes. Will only be worn with the USAF Service Uniform (Class B), Aviator Shirt Uniform or Corporate Working Uniform. With the USAF-style uniform, it may be worn under the lightweight blue jacket, the topcoat and the all-weather coat. With Corporate-style uniforms, it may be worn with any outergarment as long as it does not show beneath the lower edge of the outergarment. Gray epaulets will only be worn if the sweater is worn with the Air-Force-style blue uniform.

See CAPM 39-1