Do not use the nail and ferrel type of fasteners in the first place. they just work loose and will come down every time.
There is a new fastener on the market. It is a strong clip that fits into the bends of the gutter and has a three inch screw attached that goes through the back of the gutter into the facia board. These will work beautifully. They are about $.85 each and the spacing on the gutter is about every three feet, I like 24 inches better. Depends on your budget.
Now, with this much Ice, you might want to use this fastener with Bruce's suggestion with the straps.
In my region, we do not have that much of an ice problem, but in the Spring my gutters have held allot of hail stones.