The outside temperature is the key - combined with the length of the journey.
From the figures you mention I guess the journey will probably be 5 miles or less. You suffer from the cold weather, but don't get the mileage in to partially reverse the effects.
As a comparison our CVT will run 55+mpg in summer and 52 mpg in winter - we drive gently and on 17mile each way commutes.
Our best mpg was of course in the summer <rules out 2007 and 2008> - just short of 63mpg ( across a full tank !) - and a few people stuck behind us - LOL