So,I noticed something odd on Mt. Scott a while ago.It's a big bulbous structure in the antenna farm up there,I'm assuming it's a weather radar tower?
Any thoughts? Any idea who's it is? (KATU,KGW,etc.?)

It's a water tower owned by Happy Valley Water District. The old cylindrical tank right behind it could no longer carry the demand load as Happy Valley's population has grown considerably in the last decade. When I was engineer at 106.7, it was still on Mt. Scott (the tower is still there with antenna as a backup, I guess, assuming the xmtr is still in the small building) I used to be up there a lot. The USGS Mt. Scott elevation marker is just outside this building, opposite the side where the old water tank butts up against the fence. The new tower is on the south side of the old one, between the road and the old tank.

I always thought it was a NOAA radome.

I think they call those "onion towers" in the East and the Midwest........

Satellite imagery shows not only the globe tower, but also a second cylindrical water tank as big as the old one.

Now I'm losing confidence in my memory. I was up there in August and I thought the globe was clearly marked "Mt. Scott Water District."

A radar radome usually looks like this:

http://radomes.org/museum/photos/recent/BrookfieldOH.jpg

Here's a similar water tower:

http://www.txroadrunners.com/images/pics/gemtrailsofsouthtx/raymondville/RaymondvilleWaterTower.jpg

Ahh..Okay.

I just happened to spot this "new structure" up there,and assumed it was some kind of antenna-related gizmo.
A water tower makes sense.