Colder weather affect all vehicles, including gas models. During summer, in city driving, I average between 9-10, during winter I average between 10-11, if real cold spell, can average between 11-12. (km/per 100.)
Once I put on the winter covers, I improved by 1, so now averaging 10-11. Summer time, I don't idle, so idling for 5 to 10 minutes each morning will drive the fuel economy down. The winter covers also improve the REGEN distance a lot, not quite as good as summer time.
I'm a lay back driver, usually do 10 percent over the speed limit, don't do much flooring the diesel peddle.