A cold snap across the United States has natural gas traders hoping that stronger heating fuel demand may help deplete massive gas stockpiles by next spring, a view that has narrowed the premium for April 2016 U.S. natural gas over March. On Tuesday, the much-vaunted spread, whose extreme volatility has earned it the fearsome moniker “widow-maker,” was at just 2 cents per million British thermal units, down from nearly 70 cents on Nov. 20. March futures have rallied more than 25 percent in the last six trading days, while April’s gains have been more limited. An abrupt chill after a long stretch of balmy temperatures has forced some traders to cover bearish bets in natgas, triggering a 25-percent gain in the front-month on the New York Mercantile Exchange over the past four days. […]