We usually go that time of year, as our anniversary is Jan 26th. As others have said weather can be really hit or miss. I have been there when the highs have been in the lower 80's and I have been there when the highs have been in the 40's, and then there is everything in between.
I get cold easy so usually I pack a few sweaters/sweatshirts, jeans and maybe 1 or 2 pairs of shorts, several t-shirts, for about a week (keep in mind I don't wear shorts unless the highs are in the upper 70's). Layering is also very important, always bring some kind of pullover, hoodie or jacket with you to the parks as even on warmer days it can get cooler at nights.
Definitly check weather.com maybe a few days before you leave to finnish up (or start like me!) your packing. If it looks like its going to be cold come prepared as one year I was happy when the highs were in the 40's I was happy I brought the gloves and a stocking hat!
Jennifer