UPDATE 1-Milder weather forecasts pressure U.S. natgas futures early

* Gross U.S. natgas output in January slips for second month * Nuclear outages climb above last year and five-year average NEW YORK, April 1 (Reuters) - U.S. natural gas futures remained lower early Monday, pressured by milder weather forecasts for later this week and into next week that should point to slowing demand, despite a brief cold shot expected over the next few days. Cold late-winter weather and above-average nuclear plant outages have helped put a huge dent in inventorie