I'm in Boston, further North than you, and it's totally doable. But it all depends on your driving style _and_ your drive. The warm temperature helps enable faster warmup time, which is a big fuel burner in cold weather, but making sure you get into "full hybrid" mode will make a difference, as well as things like how long your typical drive lasts, how many miles you go. That warmup burn takes a fair distance to really recover from, though it improves in the hot summer months when you can go "full hybrid" maybe a mile from starting out, and it shuts down at stops up until that full-hybrid transition. But the fact you're in New England has nothing to do with the ability to get 40mpg. If you drive a lot of short trips, that will make much more impact on tanks, once it's warm. But I'm getting around 39 (MFD) right now just from the help of the sun warming the car even when the temp is in the 30s, I got 40mpg for a tank going from Boston to mid-Maine and back for Christmas (yes 40, highway, middle of winter, northern New England, cruise control most of the way). And as the temps rise I fully expect to get mid-40s again as I started doing last summer. But I have a 15-mile commute, drive mostly off-highway in the same kind of speed range as you. I'd do even better if it weren't for short trips like grocery shopping, laundromat, gym....

It can be done, but you need to pick up more experience, get the feel for your car, if you have any, look at other routes and see how they compare, and read tips here for what you can try. Different tips will work for different people. But definitely make sure you understand the whole "full hybrid" thing, that makes a difference.

And most of all enjoy!