HI again.
Here is a much less "scary" prediction, from Wunderground.com, a place that I find is a bit more accurate than other sites. (ETA: Sigh. It would help if I included the link):
http://www.wunderground.com/blog/shauntanner/show.html?entrynum=220
This article also gives the common name for the "atmospheric river", which is "Pineapple Express"...where a plume of moisture comes from around Hawai'i and hits our shores.
10 inches of rain sound like a lot, but remember this, too...it's been super dry here for a while, and we have very low level streams and rivers all over CA; not only that, but a lot of farmland has been parched. This will hold a whole lot of the rain that's expected, if it even goes to the max inches.
While I do expect mudslides and rockslides and the occasional flooding of streets and whatnot, I don't think it will be a deluge, and I doubt very much that it will be anything near catastrophic. If 10 inches of rain fell in, say, 24 hours...yes, that would be a bit too much, even for the dry conditions we have. But 10 inches over at least 4 days doesn't seem to be that bad, and will allow for soaking into a very dry, parched ground.
So, even after researching a bit, I'm not worried. That might be because I'm in So CA where we won't see the 10 inches forecast, but I'm still not too worried about No CA and So Oregon.
I think we'll be all right.
Best-
Herding Cats