Jake Lloyd threw four touchdown passes and ran for another score as the Thunderbirds pulled away in the second half. Dax Raymond caught two touchdowns, while Rhett Van Leeuwen and Britain Covey also caught scoring strikes.
East led 14-13 at the half thanks to touchdown runs by Ula Tolutau and Niel Robbins, but failed to score a point in the second half.
Lloyd finished the game completing 17 of 23 passes for 274 yards and four touchdowns. Raymond had seven catches for 106 yards.
In the first 4A semifinal game, Mountain Crest survived a blizzard to hold off Highland, 14-6.
Nick Taylor and Eddy Hall each scored on short touchdown runs, while the Rams committed five turnovers in the snow. Highland's only touchdown came on a 95-yard kickoff return by Malcom Card-Turner.
Hall had 110 yards rushing on 32 carries.
Mountain Crest and Timpview will play for the 4A championship November 16th at 6:30 p.m. at Rice-Eccles Stadium.
In the 3A semifinals, Dixie beat Juan Diego, 14-13, as Blake Barney scored two touchdowns on the ground. Dixie will take on Spanish Fork for the championship next Friday at 11:00 a.m.