The rattlesnake mountain shooting range west of tri cities about 35miles has NRA hoghpower/f class matches all summer, long range shooting is way more about shooting and seeing the wind effect than classroom time.At a highpower match other shooters will be happy to help you and after each shot the target will be pulled into the pits and a marker will be put in the bullet hole to identify the location of the shot so that every shot you revaluate the wind and either adjust the sight or not then you can see the results of your wind guess. The mirage is in my opinion the best reference to the wind so a typical match would have 80 shots so 80 times you can see the results of your wind guess. At the end of a match you will probably be twice the shooter you were before
Then go back every match, probably once a month for a summer or hopefully longer and at the end of the summer you will have a good idea of what goes on
Spokane also has a range to 600 yds, I shoot at Vale, Oregon every match I can, Nampa, Idaho has matches all summer and I try to get to each one. These are not benchrest matches rifles are either supported by the shooter with a sling allowed or for f class a bipod is allowed
Contact the match directors and tell them what you are doing and they will help you
If I am at Vale or Nampa I will help you