Crazy difference in MPG in different weather (1.5 turbo)

My commute to work it less than 10 miles. About 60% highway with about 40% city and some stop and go. When I bought my car in May, I was averaging a bit over 40MPG which was really impressive. It stayed that way until this winter and the crazy cold East Coast temps we have had. All of the sudden, on the exact commute driving the exact same way, I was only seeing 30MPG in very cold weather (0-30 degrees). I've never had a car with such a huge MPG difference in cold weather.

Today, it...

Crazy difference in MPG in different weather (1.5 turbo)