This happens in DC too, although perhaps to a lesser extent due to your mild climate. Some construction continues through the winter, and most carpenters and laborers are happy to work instead of draw, but nobody is framing in the snow. It's true that excavation is easier when the ground isn't muddy, so "breaking ground" in the winter could make sense. You can't pour concrete when it's freezing, though, so if the timing is wrong the rain could mess up the excavation before you get a chance to place your forms.