Established mostly grass? Late fall is best for application. Get a soil test, basic N-P-K and pH. Soils are very different around the PNW, test gives you a place to start. Your current source of N will probably be urea, 46-0-0. If it is applied on surface loss can occur with high temps so late fall to stop loss and give grass a boost early to get ahead of the weeds is best. Low pH? Lime is only real answer but tough to get it to do the job with a surface application. Using CaSO4, gypsum, for sulfur will give a neutral soil reaction and not lower pH plus give you calcium important to soil critters. 100 pounds per acre of urea and the same of gypsum would do wonders, have them blended and one tote will get it done. Might want to drag it again after the fert. Good luck!!