No, it is usually not just too cold but too wet in the Pacific Northwest to overwinter a tropical vine like mandevilla. If you do want to give it a try (what have you got to lose?) Put a potted one inside a cold room or garage and do not water so the vine can go dormant. In spring place it near a window inside a warm house an water a bit but don't fertilize until you see new sprouts of green. Place back outdoors when weather is warm in June. Good Luck, let us know if you end up keeping your mandevilla alive. Keep growing, Marianne Binetti