The average long-term U.S. mortgage rate jumped this week to its highest level in 20 years. That’s grim news for would-be homebuyers already facing high home prices caused a lack of supply. Mortgage buyer Freddie Mac said Thursday that the average rate on the benchmark 30-year home loan jumped to 7.09% from 6.96% last week. That’s the highest since April of 2002, when the average rate clocked in at 7.13%. Sharply higher rates are contributing to a dearth of available homes, as homeowners who locked into lower borrowing costs two years ago are now reluctant to sell and jump into a higher rate on a new property.