Here in Portland OR, we rarely see snow that sticks. Snow usually flurries in from the easterly winds flying down the Columbia River Gorge, initiating in colder inland climates. A few years back, we had what was referred to by many as the 80 year storm, and that inclimate weather was a result of a dipping polar jet stream that dipped down into our region resulting in snow. Then the weather warmed just a bit to start raining instead of snowing and then freezing temperatures returned. The result; snow in contact with ground, a pretty thick ice layer from the rain that froze on contact, and more snow covering the ice. Final result: madness on the roads, schools closed for an additional week and pretty horrendous damage to both the roads and the structures.
One of the signs of potential structural damage to our homes during a snow storm is ice dams. Ice dams are represented by varying sizes of ice crystals growing downward like mineral stalactites from the ceiling of a cave. 
I took this picture from my office window on January 3rd 2016. What is most important to realize, it that the ice grows in both directions. As the ice grows down it is also growing up, and if you have a composite or wood shingle roof, the ice could be growing back under the shingles. If this isn’t bad enough, the water that you see melting down and dripping onto the ground is also melting on the roof the water but has no where to go. The water just sits there, on top of the roof, not able to gravitationally flow anywhere. So, you should be asking yourself, ‘where does the water go?’. The most real scenario: Into your attic. Unless you paid a bit more for an ice dam when you last roof was installed (which isn’t a popular add on due to our lack of possibilities for snow and ice), you may need to look into adding this to your existing roof system. A roofer would come ut, remove the first three to four feet of shingles, install a specially formulated roof membrane that would resist water pass through, and re-shingle your house where the upgrades were installed. this can be costly, but as long as the roofer knows what he is doing, it should be effective. The up side is future ice dams will not allow water to penetrate the roof sheathing any longer. The downside is that’s all you get. An alternative, and less intrusive preventative measure, would be to insulate your attic.
When an attic is insulated properly, less heat escapes the envelope of your home (floors, walls and ceilings) which in turn does not allow the snow to melt as easily. If the snow isn’t melting,
ice doesn’t have the opportunity to build as readily, which increases your effectiveness to not have water intrusion issues into your attic as the picture to the left depicts (Image taken from homepartners.com). Attic insulation has a lot of positive affects on your home as well as on your monthly energy bills and interior comfort. My recommendation today is to call a local insulation company and have them come and offer you a free quote on the cost of attic insulation to the level of R-49. There are two primary options to choose from in a standard flat ceiling: Fiberglass and Cellulose. It is your choice which material you would rather have installed, and each will give you the R-Value (R stands for resistance to heat transfer) you are looking for as long as they fill your attic up to the recommended height from the manufacturer. Attic insulation height does diminish over time, but it won’t be something you need to worry about for multiple decades to come. In addition, I would also strongly recommend you have a ventilation calculation done at the same time. the additional attic insulation will slow down the attic’s ability to to dry itself out when moisture does, inevitably, pass through your attic which could result in a year round moisture problem if not ventilated correctly.
Call me if you have questions, or want to have me look at something you are not sure of yourself. I have the experiance and professional knowledge you can count on. (971) 340 8880