 NEW YORK--BUSINESS WIRE-- KBRA--Kroll Bond Rating Agency KBRA assigns a senior unsecured debt rating of BBB, a subordinated debt rating of BBB-, and a short-term debt rating of K3 to Porterville, California-based Sierra Bancorp NASDAQ: BSRR or the company. In addition, KBRA assigns deposit and senior unsecured debt ratings of BBB, a subordinated debt rating of BBB, and short-term deposit and debt ratings of K2 to the Bank of the Sierra the bank, the lead subsidiary. The Outlook for all lo 