* Front month still well below recent 21-month high * Weather forecasts mixed throughout the nation * Nuclear power plant outages remain above normal * Coming Up: EIA storage data 10:30 a.m. EDT (1430 GMT By Eileen Houlihan NEW YORK, May 16 (Reuters) - U.S. natural gas futures edged lower early on Thursday, ahead of weekly government inventory data expected to show a healthy addition to supply and amid milder, spring weather in much of the nation late this week. A long, cold winter put a huge dent in inventories and a cool spring led to a slow start to the injection season, but some recent milder weather and two weekly builds that came in above expectations helped fuel a recent sell off in gas. Most traders and analysts expect weekly data from the U.S. Energy Information Administration to show a build of about 95 billion cubic feet when it is released at 10:30 a.m. EDT (1430 GMT), a Reuters poll showed. Stocks rose 56 bcf in the same week last year and on average over the past five years have gained 83 bcf that week. As of 9:12 a.m. EDT (1312 GMT), front-month June natural gas futures on the New York Mercantile Exchange were at $4.043 per million British thermal units, down 2.7 cents. The nearby contract hit a one-month low of $3.883 last week after climbing to a 21-month high of $4.444 on May 1. The latest National Weather Service six to 10-day forecast issued on Wednesday again called for above-normal temperatures in the Northeast and Southwest and below-normal readings along the Gulf Coast and in most northern-tier states in the Northwest and Midwest. Nuclear plant outages totaled 19,800 megawatts, or 20 percent of U.S. capacity, up from 19,500 MW out on Wednesday, 16,200 MW out a year ago and a five-year average outage rate of 18,500 MW.