Jerome H. Powell said the “balance of risks” across the economy had started to shift, raising the odds the central bank lowers borrowing costs at its next meeting in September.

Powell said economic growth “has slowed notably in the first half of this year,” to an annual rate of 1.2%, down from 2.5% last year.

Federal Reserve chairman Jerome Powell signaled a possible interest rate cut in the months to come, sending stocks sharply higher.