* Front month remains below last week's 21-month chart high * Weather outlooks mixed for remainder of April, early May * Nuclear power plant outages remain below average * Coming Up: EIA natgas storage data 10:30 a.m EDT (1430 GMT By Eileen Houlihan NEW YORK, April 25 (Reuters) - U.S. natural gas futures seesawed on either side of unchanged early on Thursday, with a slight bias to the upside as traders awaited weekly government inventory data expected to show another below-average storage injection. Lingering cold late-winter weather has slowed storage injections this year, with traders expecting this week's data to continue the trend. Most expect weekly data from the U.S. Energy Information Administration to show a build of about 32 billion cubic feet when it is released at 10:30 a.m. EDT (1430 GMT), a Reuters poll showed. Stocks rose 43 bcf during the same week last year and on average over the past five years have gained 50 bcf that week. A cold start to spring, seasonal power plant outages and a tightening supply picture helped lift nearby gas futures to their highest level in nearly 21 months last week, but the nearby contract closed lower the last three sessions amid moderating weather outlooks for late this month and next month. But futures are still up about 33 percent since mid-February, after cold and lingering winter weather put a huge dent in inventories. As of 9:20 a.m. EDT (1320 GMT), front-month May natural gas futures on the New York Mercantile Exchange were at $4.156 per million British thermal units, down 1 cent, after trading between $4.152 and $4.196. The contract rose to $4.429 last week, the highest level for a nearby contact since late July 2011. The National Weather Service's latest six-to-10-day forecast issued on Wednesday called for above-normal temperatures in a large portion of the Southwest and a small part of New England, with below-normal readings across the Gulf Coast and Southeast and normal readings in the midcontinent. Nuclear outages totaled 22,900 megawatts, or 23 percent of U.S. capacity, down from 23,600 MW out on Wednesday, 24,700 MW out a year ago and a five-year average outage rate of 24,500 MW. INJECTION SEASON OFF TO SLOW START Last week's EIA gas storage report showed domestic inventories rose in the prior week by 31 bcf, below Reuters poll estimates for a 34 bcf build and the five-year average gain of 39 bcf for that week. Stocks, at 1.704 trillion cubic feet, are nearly 32 percent below last year and more than 4 percent below the five-year average. Inventories started the heating season at record highs, but three weeks ago slid below the five-year norm for the first time since September 2011. Baker Hughes drilling rig data last week showed the gas-directed rig count rose two to 379, after hitting a 14-year low of 375 three weeks ago.