If you plan to replace shingles in the winter it can be done but you have to add something to bond the shingles together.
Fix leaky roof in winter.
If a leak is difficult to find enlist a helper and go up on the roof with a garden hose.
Locate the source of the leak by examining the underside of the roof from within your attic or crawl space.
Make use of the flame carefully on the curled shingle edges.
Locate the leaking source and search for the damaged or missing shingles and make a list of the areas to be repaired.
Recaulk the corner flashing if any areas have hardened caulk.
How to repair a leaky roof from inside the house.
Now is a time when you can start planning if you know where to start.
You nail shingles to the roof of course but each shingle has a tar strip on it that causes it to stick to the shingle that overlaps it.
Isolate areas when you run the hose.
Shine a flashlight along the underside of the roof and look for a hole in the roof as well as areas that are wet or have been.
You can t fix a leaky roof from the inside so don t even try.
The roof shingles should be softened and flattened as the shingles tend to curl up in winter.
For example soak the downhill side of a chimney first then each side then the top on both sides.
The shingles can be warmed up with a propane torch.
Dig out any cracked or dry caulking that isn t properly sealing adjoining surfaces and replace with silicone caulk.
Start low soaking the area just above where the leak appears in the house.
Your best solution may be to just tarp off the problem area until the spring but be sure not to block off any venting pipes that vent out dangerous gasses.
Replace any missing or rotted siding above the step flashing on dormers.