It's not an exact science, and not all of those areas need to be at 90%. In the early 2000's I relied somewhat on JSpin's narrative TR's as much as hard numbers. And reported numbers are trail counts, not glades.Sugarbush and Mad River to Stowe, Smugglers Notch, and Jay Peak (300-325 inches) ..... at almost 90% for 8-12 weekends?
I started collecting the hard numbers twice a month in 2003-04. Numbers of seasons at least 90%:
Dec. 15: Jay 4/19, Stowe 1/19 (4 others at 85%), Sugarbush 2/18, Killington 1/19
Jan. 1: Jay 6/19, Stowe 5/19, Sugarbush 5/19, Killington 3/19
Jan. 15: Jay 5/19, Stowe 7/19, Sugarbush 9/19, Killington 4/19
Feb. 1: Jay 13/19, Stowe 14/19, Sugarbush 15/19, Killington 9/19
Feb. 14: Jay 14/19, Stowe 14/19, Sugarbush 19/19, Killington 11/19
Mar. 1: Jay 17/19, Stowe 14/19, Sugarbush 17/19, Killington 11/19
Mar. 15: Jay 14/19, Stowe 9/18, Sugarbush 14/18, KIllington 8/18
Apr. 1: Jay 12/18, Stowe 7/18, Sugarbush 10/18, Killington 4/18
Apr. 10: Jay 8/18, Stowe 1/18 (3 others at 85%), Sugarbush 1/18, Killington 1/18
This is the first time I've gone through those stats this way, and it implies an average of 8 weekends over 90% for Jay. Sugarbush is very aggressive about opening terrain at low tide (like Wolf Creek, Crystal, Bridger, Red Mt.), so I pay more attention to what Jay and Stowe report. I do not track MRG and I have Smuggs on handwritten papers for a decade or so but not in the tracking spreadsheet. I believe it would be very rare for MRG/Smuggs to have higher percents of terrain open than Jay/Stowe
While my twice a month data collection is systematic, the weekly charts are more of a seat of the pants exercise, often looking at TR's early on and OpenSnow in later years to get a handle on weather/conditions. The weekly chart might reflect more like 80+% open than 90+%. There's also the alternative criterion of 50+% open with winter snow surfaces, which probably picks up a couple of extra early season weekends on average. The excess of the chart vs. the numbers above is mostly before February.
My first time at Killington was Oct. 28, 1988 and it was definitely on Upper Cascade with midloading. That probably applied to Upper Downdraft on April 29, 1990 too, though I believe there was an exit trail to the base on the latter date.
Thankfully I skied all of those on my one day at Stowe.Stowe - 'Front Four' (Starr/Goat), Chin Clip and Spruce are often not available.