Well, I'm about 200 miles south of you, so I may or may not be in similar conditions. I drive a 2005 HCH.

When things are cold, (semi)-windy, and wet/snowy, I'm as low as 35mpg. Some of these miles are my 3-mile highway "accelerate to 65mph and I'm there" commute to and back work. Some miles are typical suburbia driving. In these conditions, I get about 40mpg on a 150 mile freeway trip.

When the temps reach 45-deg, I get about 40mpg, and 43.5mpg on the freeway. When the sun is out I swear the mileage numbers jump up another 2-4mpg, but I haven't been able to burn a full tank with the sun

I'm also working on proving that playing "The Velvet Underground" ups the mileage even more, but that might just be me.

I'm pretty close to 5000 miles, but I'm pretty sure I've hit my break-in period.

Just to be curious, are you running your compressor a lot, ie in defrosting your windshields? That could have a decent effect on your mpg.