U.S. natural gas prices finally retreated Tuesday after the longest stretch of gains in two decades, but warmer forecasts and a tight global market are seen keeping the outlook bullish.

Unrelenting heat from the East to West Coasts, coupled with increasingly strong international demand for liquefied natural gas (LNG), helped the Henry Hub front month contract to nine straight days of gains that ended Friday. The August contract lost 7 cents on Tuesday to close at $3.637. LNG exports, which began from the Lower 48 states in 2016 and have gradually increased since then, played a key role in the recent rally. 

“Despite stronger commodity prices, U.S. dry gas production has flattened and is not increasing fast enough to offset LNG demand. Strong cooling demand and relatively low...