Answers are interspersed...
Just applied for a CPL in the state of WA, and read through the RCW but was unsure of when I need to notify an officer I am armed
There is no duty to inform in WA State. However, it is a courtesy that is greatly appreciated. If you are stopped by an officer, something along the lines of: "Before we go further, I want you to know that I have a valid CPL, and I am armed right now. What do you want me to do?" This prevents any possibility of misunderstanding--because if I'm the one stopping you and I see a firearm within reach BEFORE you let me know, things can get uncomfortable. It also identifies you as one of the good folks that went to the trouble of carrying legally.
and more specifically what abilities they have once notified.
No more and no less than any other time.
When I notify at a traffic stop (or any time I'm talking to an officer that I know is an officer - not off duty/undercover that I cannot identify) are they allowed to take possession of my firearm?
Yes--although in most cases we will not. Of course, it differs from officer to officer--but a calm demeanor and steady behavior will do a lot to keep things on an even keel.
Can I refuse to hand it over, citing my 4th amendment rights?
Friend, first things first. The only reason I will relieve you of the firearm is during the investigation of possible criminal activity--in other words, if reasonable suspicion is present. (See Terry v. Ohio, 386 US)
Moreover, if I am contacting you for official reasons, the LAST thing you want to do is to place your hands anywhere near your gun. Any officer that has successfully passed FTO phase will have you turn around and will quietly relieve you of the firearm. Again, though, that's not normal during a regular traffic stop.
One other thing...if I have articulable reaasonable suspicion that a crime is being/has been/will be committed, and you are tied into it, you can bet that you will be (at least temporarily) relieved of your firearm. In that case, you do NOT want to refuse to surrender the firearm. Trust me, you don't.
If I cite the 4th amendment, can I refuse to hand it over, or must I simply state that I do not agree with handing it over, and then comply?
Cite the 4th all day long. Neither myself or the other officers I work with or know are in the habit of violating anyone's civil rights. I personally take great care to ensure that the rights guaranteed by our Constitution are not violated. After all, it IS part of my oath as a peace officer.
However, in this aspect, there is one simple way to avoid all the hassle--and that is to not break the law. Do NOT get involved in fights, don't abuse your spouse, children or neighbors, and don't get involved in anything that may even seem illegal, and your scenario will never happen.
Now, my advice is to stop worrying, get yourself some quality leather to carry your piece in, and head to the range.
Cordially,
your friendly neighborhood Powderman