The warmer water also attracts zooplankton which is food for walleyes and forage fish. This time of the year when the water is cold one needs to use a slow presentation. Jigging works well this time of year especially if you tip your jig with a plastic twister tail and or a fathead minnow. If you plan to vertical jig use enough weight to tap the bottom and keep your line up and down. Too much weight will cause you to snag up and too light a jig will cause you to lose contact with the bottom.
Experimentation is the key to finding the proper weight.
If you work a jig slowly and use a weedless jig like the Bait Rigs Weedmaster, you can cast to shallower water and work the jig back slowly. Remember the key this time of year is a slow presentation. Another rig that works is a plain hook, like a VMC colored hook with a bead above the hook and a split shot above the bead anywhere from 1 to 2 feet. This simple approach works when other techniques fail. Sometimes simple is better.