Not since the 1950s, Federal Reserve Board Chair Jerome Powell said this week, has inflation and unemployment remained so low for so long.

Speaking in Boston on Tuesday, Mr. Powell depicted a throwback to economic conditions seen only briefly in post-War U.S. history, and fresh data released Thursday and Friday reinforced Mr. Powell's "remarkably positive outlook."

In the 88% of the U.S. economy outside of the manufacturing sector, purchasing activity soared in September, climbing to the highest level since inception of the index in January 2008. According to Thursday's report from the Institute for Supply Management, the forward-looking new orders component of the index slowed slightly from August but remained very strong.