Shares of Spokane-based Sterling Financial Corp. have climbed this week following reports in financial journals that it may be purchased for $1.8 billion by Umpqua Holdings in Portland. Sterling has not commented but Bloomberg, along with The Wall Street Journal, report Sterling has been meeting with potential buyers this month. An announcement could come as early as today. Sterling shares had jumped more than $3 per share since the start of September in heavy trading as speculation took root in media reports this week. Shares closed Tuesday at $27.14 a share. Such a deal would be a blockbuster deal for the Northwest. And it would cause some uncertainty for Spokane, where Sterling remains a major employer and community stalwart even though it is now controlled by Warburg Pincus and Thomas H. Lee Partners, private equity firms that purchased large stakes in the publicly traded lender. The two banks combined would have about $20 billion in assests and about 400 branches.