temp-mpg relationship

[Mullen, Shaun]

At the risk of starting a Thread From Hell, would any of our more
tech-oriented listers like to take a whack at why, as temperatures rise in
the late winter into the early spring (in the Northeast U.S., in this case),
gas mileage improves?  I was averaging 20.1 mpg in February.  I was
averaging 21 mpg in March.  Now I'm nipping at the 22 mpg mark.  Type of
driving and type of fuel are not factors: I have not altered my driving
routine -- about 75 percent highway and about 25 percent city.  I have not
altered the kinds or octane of the fuel I use.

Shaun Mullen
Gasoline Alley, USA