-Buttercup Wildflower, photo by Steve Dawes 2014
Fuel Efficiency is effected a lot by the weather. Some experts feel that really cold weather (sub-zero) can diminish fuel efficiency as much as 50%.
Air becomes denser in extreme cold and presents greater demand by vehicles to push through it. Cold tires and cold pavement do not provide as much friction.
Fuel systems find it more difficult to atomize fuel and air.
Everyone notices that fuel economy drops significantly in cold weather.