The Tposts going up a foot on the outside of panels really helps support the arch to hold all that snow, and those look like 'hog' panels which are one of the strongest panels with smaller hole spacing than some other livestock panels. The difference in stiffness between hog panels and cattle panels is significant. The lattice adds some strength too.I've notice similar builds with wood center supports and wood framing on the ends, but I'm not so sure it's needed.