I live in Central Pennsylvania, which has similar seasonal temps to the Pacific Northwest. We're starting to finally get out of the 60's-70's this week, due to horrible thunderstorms, and last night it got down into the high 40's here. Central PA is tough, because you have to run your AC during the day, and then you have to turn on your heat once the sun goes down in the spring and the fall...
As Noodles mentioned already, it's much more important to make sure that your bird doesn't just go from inside where it's 65-70 degrees to directly outside where it's 50-55 degrees, as this can cause a lot of stress and actually shock if the temp change is drastic enough...Think about it this way: Wild birds who live outside full-time are usually fine until the temp gets down into the high-30's to low 40's, essentially until it gets down near freezing. And that's because they are continually outside in the changing temperature, and experience it gradually, instead of a pet bird who is living inside most of the time in a temp range between the mid-60's and the low-70's, and that is suddenly exposed to a drastically colder temp all of a sudden. Birds are well insulated by their feathers and can live continually in very cold temperatures, even parrots...Take the Quaker Parrot for example, we have large, wild Quaker Parrot colonies here all over the Northeast US, in Maryland, Delaware, New Jersey, New York, Connecticut, Massachusetts, Ohio, etc. They live outside here full-time, all year long, and survive literal blizzards that dump feet of snow at one time. Yes, they build community nest complexes, but it's not like they have central heat, lol...
As far as taking your bird outside, flight suits in-general are not very protective and I wouldn't imagine that they add much warmth for your bird at all (unless you have a different type of flight-suit than I'm thinking of, as most of the ones I've seen are made from a polyester or rayon type of material, and they are extremely thin). So unless you have a flight-suit for your bird that is made out of a much warmer-than-normal material, such as fleece, wool, etc., and is much thicker than the average flight-suit, then I'm not sure that this is a solution. However, you can purchase special clothing/flight-suits that are actually made for cold weather, and as such are made from extremely warm, insulating material, and are much thicker than the typical flight-suit is (by definition, a "flight-suit" is made for them to be able to fly in, as as such they generally aren't very heavy/thick)...But then again, your bird's legs, feet, and most importantly his head are going to be still be exposed...And they are of-course going to lose the most heat through their head!
I think this is a "use your common-sense" type of situation. Again, birds are going to lose most of their heat through their heads, just like we do, so you certainly don't want to take him outside when it's down into the 40's or below without him being inside of a carrier that is covered. If you are just talking about taking him outside on your shoulder for a walk (I'm assuming you use the flight-suit like you would a harness, and he's attached to a leash, I hope), and the temperature is in the 50's or above, then he should be fine, as long as it's not raining and he doesn't get wet. If you have him outside for a walk in his flight-suit and he's constantly "fluffed-up", shaking, trying to cuddle/snuggle close against you, then he's too cold. But I've had my guys outside wearing only their Aviator Harnesses, sitting on my shoulder and walking around the neighborhood, in the woods, or going in the car with me and then out into stores, etc. when the temperature was as cold as at least 55 degrees with no problems at all. Just use your common sense and he'll be fine, and he'll certainly let you know if he's too cold.
just getting them "a sweater" made of a sock will help a bit, go for windresistant material for really cold days )
