50s aren't bad, depending on humidity, wind, and sun sometimes I'll just grab a warmer short sleeve jersey. (After you ride long enough, you may accumulate a wide variety of jerseys!) Below that you may want a t-shirt (aka "base layer") under a long sleeve jersey, ear warmer/headband, and knee warmers. Low 40s call for real tights and a jacket. Below that, check out clothing posts in the winter riding forum.