Probably ice dams on the roof eave, no Ice & Water Shield underlayment or perhaps poor flashing so the water from melting snow is getting in. A classic freeze-thaw syndrome in cold climates. It's usually necessary to tear the roofing off at the eaves and put it back right.

I'd say not probably, but definitely an ice dam issue.

How old is your roof? Does the outside fascia above the window go straight up to the underside of a large overhanging soffit? Is the other bay the same type of window on the same side of the house?

If you pull off that trim board I suspect you'll find that the area above it likely has ponded water. As water is added to the "pond" it finds its way to the inside space.

If you can, go up in the attic with a stron flashlight and look at the undersidfe of the roof at the outside perimeter. See if it's wet and to what extent. If you see a significant amount of water and still have a lot of snow in the roof, It might be worth it to look into haing a roofer ciome and remove whatever snow he can.

That "leak" will likely continue until the snow is gone or iuntil the melt can freely flow off of the roof. This winter in New England you're not alone.

I cannot see any water in the attic.
But I think I will have someone over to come and clean the ice dam. Much thanks for your help.