When you are inspecting your roof for the winter ahead, look for raised shingles. If you see any, in all probability, it is caused because a nail has popped up and lifted the single. As soon as possible, you should have a professional roofer inspect your roof to make sure it can survive the winter and discuss what needs to be done.
Nail pops can be caused by a variety of reasons. When the temperature changes, expansion and contraction can cause the nails to pop up and lift the shingles. You should also make sure your roof is adequately ventilated.
Other causes of nail pops can be that the shingles were not nailed tightly when the roof was installed. Additionally, the installers could have used nails that were too short. It really is not uncommon to have a few nail pops, but left unattended, the roofing system will be compromised, and water will penetrate the wood causing leaks and interior damage.
There are lots of reasons why nail pops can occur, but the important thing is to take care of them as soon as you notice raised shingles. If the nail pops are dealt with immediately, a fix can be quite simple: remove and replace the loose nails and seal the shingles down. Because a nail pop brings the shingle up with it, water penetration under the single can occur, or strong winds can blow the shingle off the work. Call a roofing professional to check it out.