I live in Boston and have been taking LO out for walks up until 2 wks ago. Temps were in the mid-30s. I cover DS with 2 blankets, plus hat, and I check his cheek/nose every now and then to make sure he's warm enough. On windy days, i put on a carseat canopy to block the wind.
Sadly, now we have a blanket of snow/ice on sidewalks and temps are in the teens and low 20s, so no more walks for us!