2:51 (Dow Jones) CME lumber futures posted additional gains on firming cash prices following an explosion and fire late Monday that destroyed the Lakeland lumber mill in Prince George, British Columbia. Follow-through buying ensued in futures as other suppliers of stud lumber raised their quotes on tightened supplies, brokers said. Short covering, or exiting of short positions by buying them back, contributed to the gains. May hit a nearly seven-week high and July a six-week high. May closed up 50 cents per 1,000 board feet, or 0.2%, at $277.90. July gained $3.40, or 1.2%, to $282.50. Cash prices $287-$292. (curt.thacker@dowjones.com)