Winter and Fall
Your fuel economy will be reduced significantly in the winter. This occurs for many different reasons. One reason is that it takes longer for your engine to warm up in order to reach its most fuel-efficient temperature. There are several other factors such as your heated seats, defrosters, and even your four-wheel drive can lower your fuel economy.
There are some things you can do to help your fuel economy despite the winter months. If possible, park your car in a warmer place; in a garage, or maybe even in the sun - this will increase the initial temperature of your vehicle. Check what type of oil your vehicle uses for cold weather and minimize idling your car to warm it up (no more than about 30 seconds).