You will be fine for this weekend. I rode last friday afternoon and even though it was 34, everything was still frozen, minus a few wet spots along the fields and other normally wet areas. With the temps that are forecasted, it will be rock solid. The time I rode there the week before, the yellow trail (I normally avoid this like the plague)was frozen except for one or two spots where tires broke through the ice.
I was today from 10-12 and the park is frozen and super fun. The stream crossing is pretty high, which explains why there are FEW tracks in that direction. Thank the good lord for the man who invented gore tex.