Welcome from North Central Wa! (The Dry-Side!)
The Tri-Cities group out in Pasco is probably your best bet. (Especially if your flying the Arreux..... been there, flown that....it likes to fly so Pasco is a GREAT area for that type of stuff!)
I am in Wenatchee area by the way, and as I understand it there once was a flying area just NW of here but no more. Don't know details. (but I would not be opposed to trying/helping to get that going again)
Going south there is OROC, (Portland area...a couple hundred miles distance-wise but of course nooooottt Traffic-wise!) however their MP/HP site is wayyy out in Eastern Oregon and that is a hike to be sure! (A very worthwhile trip, one, but still its a lonnng way!.... and don't paint your rocket 'Sage' colored!)
There is also a group down near the Colombia Gorge, that holds MPR/HPR near Goldendale, (No easy way from Seattles... I-5 to 14 to 97? but pretty!) however they don't seem to hold those very often. (Never made it to one of thier launches, but i'd like to)
There are a couple of groups in the Seattle / King County, but I am not sure they are very big fields.... 60 acres in Redmond - when its not infested with Youth Soccer events (My kid being one of the infesters
) is big, but not sure I'd want to fly an Arreux there, (of course I put H's in mine....
So it get up there!)
SPARC is Spokane,
In summation, SPARC, OROC, TriCities are all great bunch of folks, - and the *big* flying areas are for the most part over on this side
Anyway, again Welcome!