There's a steep precipitation gradient down the valley, getting drier as you go east, out of the mountains, to lower elevation.
Snoqualamie Pass 105" precip/yr, 440" snow/yr
Stampede Pass 85", 439"
Lake Kachess 53", 160"
Lake Cle Elum 37", 146" (5 miles NW of Roslyn)
Cle Elum 22", 81"
Ellensburg 9", 21"
Ref: Western Regional Climate Center
http://www.wrcc.dri.edu/summary/Climsmwa.html
You can see this in the vegetation. Hemlock around Lake Kachess, pine through Roslyn to Cle Elum, the valley floor is open grassland from Cle Elum to Ellensburg, and sage past Ellensburg (where it isn't irrigated farmland).
Twisp is drier, and has slightly colder winters and warmer summers, than Roslyn or Cle Elum.
Cle Elum has a big safeway and small grocery, no organic food stores. It has all your other basic shopping and services.
There are no orchards or meat packing plants anywhere near Roslyn.
The Cle Elum River flows right down the valley (although I'd guess the riverfront is all private land). It flows from Lake Cle Elum, which is a reservoir just north of Roslyn. Lake Kachness is another large reservoir west of Roslyn. There's lots of trails into national forest all around the area.
Timothy and orchard grass hay shouldn't be any problem (I dunno about bermuda); there's plenty of horses and outfitters in the valley.