Heating the great outdoors are you....yup, this creates a problem.
The areas where you get the refreeze are the areas where the insulation coverage is at it's least.
The basic idea is to let the roof be a constant temperature. The areas which cause problems have leaks . This is where you need to start. No amount of ventilation is going to help this issue, especially in the area you live in. My cousin lives near Dartmouth College, I know how cold it gets up there when we go for a dogsled ride.
The gable vents may actually cause more issues due to the cross ventilation you try to introduce. The venting you have now works like a chimney, cold air drawing up the roof traveling to the warmer area at the top. If you blow a breeze across this...you cancel out what is working.
Maybe you can seal the leaking joints better at the gambrel transition. This is a typical area we find issues with our Thermal Imaging camera. As for the skylight roof windows, there is no cure except removal, or lowering the temperature in the upstairs...bringing you back to where you started. Unfortunately This is the reality of roof windows, they loose large amounts of heat, you can always see this from the condensation on the inside...and the water staining which most folks think are leaks in the window.
To summarize, the design of the roof is the issue. The break in the roof design allows for an area which leaks the heated air into the attic space. I do not like to point fingers ...but the insulation company probably does not understand this issue...and some insulation is actually missing at the top hinge part of this design. The insulation touches at the bottom, where you see it , but not in that triangle hinge area above.
I hope this makes some sense, please ask away with anything you need clarification on.