Weibring, who finished sixth in last year's event, was 5-under on the back nine, including four birdies on the last six holes. His two-round score of 13-under, 131 is a 36-hole tournament record.
Thorpe, who has won at least one Champions Tour event in seven straight years, but is winless in 2007, made a double-bogey at 16 and a birdie at 18 to finish with a 68.
An intermittent light rain kept the greens soft, but the wind picked up at the TPC Twin Cities. Just 14 players broke 70 Saturday, compared to Friday when 41 players shot in the 60s in calm, sunny conditions.
Tom Watson (65), who won the Senior British Open last week, leads a quartet of players three strokes back. He is joined by Curtis Strange (66), who birdied the last four holes, Tom Jenkins (70), who was a co-leader after the first round, and local favorite John Harris.
Harris of Edina, Minn., got to 10-under with a birdie at No. 12, but a double-bogey at 16 dropped him to 8 under, before he eagled the par-5 last hole for a 69.
Craig Stadler, who shot a 70, was 11-under after 12 holes, but finished at 9-under, tied with Bruce Lietzke (68) and John Jacobs (70).
Defending champion David Edwards was at 139, eight shots off the lead.