Around the half of movie, camera shows Molly's Reach restaurant for a several seconds and it's snowing. In the following scene, camera is now inside the restaurant, and suddenly there is no more snowing (you can see through the large windows). 10 seconds later, Christina enters the restaurant, and no snowing from that angle, too, and is even sunny.
The lighthouse shown near the end of the movie is obviously photoshopped into the background. Part of the Christmas wreath is missing on it. It probably should have been up higher on the lighthouse. Like shown on the poster ad. A wreath that big would have been enormous if real.
The movie takes place in Nantucket, the island of Massachusetts, just before Christmas. In reality it was shot in BC, Canada but it changes nothing for weather and climate as movie was obviously shot in the early autumn. The only time you see winter is in the stock footage, and production used them a lot in between scenes. You see a lot of snow and bare deciduous trees in stock footage, and in the following (real movie) scene suddenly everything is green (deciduous trees), and there are even flowers. They added a bit of artificial snow on some trees and on ground in the close shots, but mostly not.
During the last few minutes when everyone is sitting around the fire roasting marshmallows, you'll see a man in a short-sleeved orange/red t-shirt walk out from behind the trees, see that he is in the shot and duck back behind the trees. You might be able to pass it off as a resident if he was dressed appropriately and did not react to the camera the way he did.
First, Nantucket has three lighthouses and the one shown is not on Nantucket; they are all on flat land with sand and grass. Second, Nantucket does not have tall pines; it is mostly scrub, sea grass and sandy beaches. Third, there are not any mountains anywhere near Nantucket.
The real Nantucket is much more densely packed, the architecture is all wrong, the lighthouses aren't Sankaty or Brant Point. None of the villages are shown. It is flatter without the hills, much sandier, fewer coves and islands.