NEW YORK, Aug 20 (Reuters) - Wall Street rallied to close sharply higher at the close of a tumultuous week on waning concerns over whether the U.S. Federal Reserve could begin tightening its dovish monetary policy sooner than expected. While all three major U.S. indexes ended solidly green, all posted weekly losses after a steep mid-week sell-off pulled the S&P 500 and the Dow away from a string of record closing highs. "Towards the beginning of the week you saw traders balancing their books ahead of the Fed statement," said Matthew Keator, managing partner in the Keator Group, a wealth management firm in Lenox, Massachusetts. "And once the statement came out, you saw a bit of "sell the rumor buy the news."" Market-leading tech and tech-adjacent megacaps, which weathered the pandemic recession better than most, once again provided the biggest boost. Growth stocks were also given a boost by U.S. Treasury yields, which ended the week lower due to concerns the health crisis could be a longer than expected hindrance to economic revival. Announcements from a host of Asian nations that they are implementing drastic measures to curb the resurgence of COVID-19 due to the rise of the disease"s highly contagious Delta variant, put a damper on stocks associated with economic re-engagement. read more Mixed economic data from the U.S. and China suggested the ongoing recovery from the most abrupt recession on record has passed its peak and lost some momentum. Market participants now look to next week"s Jackson Hole Symposium, a gathering of major central bank leaders, for clues from Fed Chair Jerome Powell regarding the expected pace of recovery and the timeline for policy tightening. "We’ve seen times in history where the Jackson Hole Symposium has drawn a lot of eyeballs but this year more so," Keator added. "The Fed might use this opportunity to communicate what their plan is going forward." Unofficially, the Dow Jones Industrial Average (.DJI) rose 222.15 points, or 0.64%, to 35,116.27, the S&P 500 (.SPX) gained 35.79 points, or 0.81%, to 4,441.59 and the Nasdaq Composite (.IXIC) added 169.95 points, or 1.17%, to 14,711.73. All 11 major sectors of the S&P 500 ended the session higher. Second-quarter reporting season has essentially run its course, with 476 of the companies in the S&P 500 having posted results. Of those, 87.4% have beaten consensus, according to Refinitiv data.Farm and construction equipment manufacturer Deere & Co (DE.N) beat quarterly profit expectations and raised its full year guidance due to robust demand read more . Still, its shares lost ground. Bristol-Myers Squibb (BMY.N) advanced after the U.S. Food and Drug Administration approved the drugmaker"s cancer drug Opdivo. U.S.-listed shares of China-based tech-related companies oscillated as market participants digested recent sell-offs resulting from Beijing"s ongoing regulatory crackdown, which has wiped half a trillion dollars from Chinese markets this week. read more