A cold front blew down from Canada this past weekend and Saturday was the first day I found cool enough to wear tweed around San Francisco. Tweed is a relatively loose weave and the gun club patterned jacket in the photo is only partially lined so it can be worn comfortably up to about 70 F (21 C) even though the cloth weighs 18 ounces.
Gun club tweeds are variations on the Shepherd Check, which in black and white was the original tweed pattern. According to E. P. Harrison's book Scottish Estate Tweeds, the basic gun club design was exported to an American shooting club in the 1870s for their club colors and then re-exported back to Britain.
The jacket is combined with old slip-on Peal shoes from Brooks Brothers, wide wale navy corduroy trousers, an ecru silk shirt, a paisley ascot and a silk pocket square in a second paisley. If I wanted to dress the jacket up a bit I'd substitute flannels for the corduroys and don a necktie.