U.S. natgas futures seesaw early, tighter supply supports

* Front month remains below last week's 21-month chart high * Weather outlooks mixed for late April, early May * Nuclear power plant outages remain below average * Coming Up: Baker Hughes gas drilling rig data Friday By Eileen Houlihan NEW YORK, April 26 (Reuters) - U.S. natural gas futures seesawed on either side of unchanged early on Friday, with concerns over a tighter supply picture this year after another light weekly inventory injection underpinning prices. Invento