Natural gas prices closed slightly higher Monday, rebounding from last week’s 2 1/2 year low after weather forecasts raised expectations for heating demands by showing severe cold and snow spreading over the east. The front-month March contract settled up 1.8 cents, or 0.7%, at $2.597 a million British thermal units on the New York Mercantile Exchange. Gains had been as high as 3% immediately after electronic trading opened Sunday evening, but the contract retreated back to unchanged in the morning. Forecasts flipped temperatures from above-normal to below-normal for large portions of the Midwest and Southeast this week. At least two shots of arctic air are also headed into the Northeast through the middle of the next week, private forecasters said. The cold temperatures are likely to drive a high amount of heating demand with some of the most severe weather focused on New York and Boston, according to Weather Services International in Andover, Mass.