President and Chief Executive Officer of the U.S. Federal Reserve Bank of San Francisco, John Williams, addresses a news conference in Zurich, Switzerland September 22, 2017. REUTERS/Arnd Wiegmann/File Photo

NEW YORK (Reuters) - A flattening U.S. yield curve in December, which was close to being inverted, was “flashing red” about a deceleration in U.S. economic growth heading into 2019, despite some solid data at the time, New York Federal Reserve President John Williams said on Friday.

The yield curve flattens as the gap between short and long-dated yields narrow, suggesting investors’ worries about a slowing economy.

The yield curve inverts when shorter-dated yields rise above longer-dated ones. An inverted yield curve has preceded all U.S. recessions in the past 50 years.

Williams was giving closing remarks at a conference about quantitative tools, jointly sponsored by the New York Fed and the Atlanta Federal Reserve.