U.S. stocks surged on Feb. 6 in a stunning turnaround that saw the blue-chip Dow soar more than 1,200 points to pierce and close above the 50,000 mark for the first time ever.

The Dow Jones Industrial Average reached 50,000 for the first time ever on Friday, a milestone that capped a volatile week in which markets appeared increasingly unhinged — before abruptly bucking hig...