could cold weather cause worse mpg?

My daily driver is a 91 Suzuki swift 1.3 2barrel 5 spd. I originally purchased about a year ago and my first fill up MPG was around 28. After changing plugs wires cap rotor fuel filter the MPG started to get better each fill up all the way to my best 45. But the last few tanks have dropped to around 38-39. My commute has not changed or my driving habits only change has been winter weather so back to my title, could the temp drop cause a drop in fuel mileage?

 

They put ethonol in our fuel and lowers the economy. The cold should benefit our economy unfortunately the government knows best.

 

Short answer is yes

 

yeah its the gas, always worse in the winter but keeps moisture from building in the tank

also letting the car worm up for longer add up to quite a bit of used fuel

 

Thanks for the quick reply guys.