If the undergrowth is growing then the ground temp is fine, low temps are far better then over 55 all the time. Warmer weather helps speed growth but in return shortens the season. Yellows start out as greys btw, it's ultraviolet radiation that changes them yellow. So the more uv rays a morel gets will change them quickly, that's why greys are always in shadier areas but will still change to yellows if left to grow and temps stay low with plenty of rain. The more shade the longer it will take but not all will survive long enough. A warm up over the next month will mean a long season even if the undergrowth is out of control, it makes it a challenge but in return helps shade the great morel from the mean old sun. Morels are made up of a lot of water and the sun takes it away. If the currant conditions hold it will be a great season. The shrooms will still get big, just might take an extra week of growing time.