The Jets’ defense was severely hampered by a nose tackle with a back injury last season. Now they are dealing with another one — they just have to hope it’s not as serious. Kenrick Ellis has missed the last two days of practice after injuring his back weightlifting. Last season nose tackle Sione Po’uha hurt his back lifting and missed most of training camp. He missed four games in the season and was ineffective when he played. Ellis is much younger than Po’uha and coach Rex Ryan said he thinks this is just a short-term injury. “I know [it’s] a day-to-day thing so I’m certainly hopeful it’s not as bad as Sione’s was that kept him out of a lot of training camp” Ryan said yesterday. “Hopefully it’s not like that. To me it’s a day-to-day type of injury.” The Jets run defense was 26th in the NFL last season and a large part of that was because Po’uha was not his normal self occupying blockers. * It was 53 degrees windy and raining when practice began. “Without question that had to be the coldest training camp day I’ve ever been a part of” Ryan said. “That’s about 30 years worth.” The cold weather seemed to affect the offense more than the defense. “That was chilly ... almost as chilly as the offensive performance today” Ryan said. “Not a good day at all for the offense. Obviously we’ve got to straighten a lot of things out before we play Jacksonville. I’m disappointed because I thought we’ve been doing some good things out there.”