I guess that snow stake is the official answer to the OP's question: Dec 12, 2018 is when you STOP fretting about conditions at Whistler. So now he can start fretting about the crowds and lining up and over paying for everything.
^^Dead on. I was at Whistler this weekend and can confirm that it is underway, in all of its splendor. And there will be snow this season.
Saturday was beautiful, cold, clear and dry. It was almost like skiing in the Rockies. But limited terrain made lift lines a zoo. Whistler certainly has strong synergy with Vail on that aspect of the experience.
The Peak would have been epic - if we had been willing to stand around in the cold for two hours in line. The group in the front of the line (who did not include us) got in some poor man's heli skiing once it opened up. And they gave us a good show as well. But the line never receded because that was the only high Alpine terrain open at either mountain.
Sunday was really nice for first tracks, even being limited to the old school Whistler chairs (Red/Green). About 10-15 cm of classic pasty PNW "powder." But it warmed up in a hurry and with high winds, poor viz, the Alpine shut down and the snowline creeping up to mid-mountain, it was the classic Whistler experience. Drenched at the end of the day. We had fun because it is skiing, we were with friends and it is an easy drive from Seattle. But I still can't fathom why anyone from outside of the PNW would book well in advance, fly over UT, CO, WY, MT, and pay silly prices for variable conditions. But when it is on. . .