I have caught fish in 4 ft of water or less with the temps in the 40's. If the barometric pressure brings up the plankton and the wind blows it up in a bay the baitfish will follow. And so will the crappie sometimes. Remember...if the deep water is in the forties or less then a sunny day in the afternoon the shallow water may be the warmest water in the lake for a while. The fish will move back out...but if your timing is right you may catch them shallow. I will look shallow anytime of the year...when conditions are right. I look for shad flipping a lot of times. If they are feeding on plankton they "flip" the surface with their tails. I see that I fish under them. Also a dark bottom,grass,rocks,etc on the bottom on a sunny day will warm the water even more.