In the last month, there have been as many as four-five trains a day running over Stampede, the majority of them being eastbound empty grain trains from Tacoma (X-TAC___).
Currently the only westbound train running on a "schedule" is the Pasco-Vancouver, B.C. (Thornton Yard-CN) manifest, which typically leaves about Pasco Yard around 0800, however, whithin the last week or so, the PASVBT has left before daylight. I have also noted the PASVBT does not always run the pass, especially on the weekends.
The Pasco crew has been changing trains at Ellensburg early afternoon (~12-2) with the empty grainer crew, but sometimes that does not always work according to plan.
Easrly morning to mid afternoon, you should be able to catch an eastbound train and mid to late afternoon, the westbound should hit Stampede.
There is quite a bit of discussion on railroadforums regarding Stampede:
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