You do need to ventilate the attic. Opening the window will probably suffice for the rest of the winter (and beyond), especially if there are two windows that can provide cross ventilation. Most large hardware stores should have those horizontally adjustable inserts that fit under the lower window sash. The ones I'm thinking of have louvres and screens and are only about 6 to 8" tall. They're specifically designed to provide ventilation. You made need something more than this, like a fan, for the summer to keep the shingles from overheating.

Venting the attic will help but in the winter the attic air should be dry unless there is excessive moisture entering from roof leaks or rooms below. Check for leaks and make sure the exhaust fans are working and being used in the bathrooms.

make sure the exhaust fans are working and being used in the bathrooms. and not venting into the attic. Basic, you'd think.
You'd think wrong.

Unfortunately, we do not have any exhaust fans in the bathrooms or kitchens. It is a 2 family house that needs ALOT of updating! The apartments are upper and lower, we live in the 1st floor and tenants live in the second floor. Should exhaust fans be our next project?