I loved watching the people follow the shade under that weird dance tent in 2009. It casted the weirdest shapes onto the grass and there was always a hoard of people stuffed right inside them.
Any fence that was sufficient enough to cast a shadow had hoards of people cowering under the shade as well. That was definitely a sight that was unique to 2009, at least from my perspective. I recall having like 3 hours on one of the days where I didn't have interest in any of the bands and spent a good chunk of that time just trying to find any place to sit down that had shade.
That looks pretty great, however I don't trust a forecast more than about three days out. It's a pretty good assumption that it'll be similar to that though, given that weather is easier to predict at the Gorge than on the west side of the Cascades.