The lower Madison is cold all week long. If you head out in the below freezing temperatures nymphing will be the best option San Juan worms, sowbug/scuds, Zebra Midges, and smaller Perdigons should work. Fish will sitting in slow deep water for the most part. Swinging a bugger or soft hackle with your trout spey rod can be good throughout the winter.
The lower Madison River is considered to be the Madison River from below Ennis Lake, downstream to the headwaters of the Missouri River. This section of the Madison flows through the Beartrap Wilderness Area in a narrow gorge characterized by some serious whitewater and difficult access. Once the river leaves the Beartrap Canyon, the river dramatically changes character, becoming wider with a seemingly gentle flow all the way to Three Forks, where it joins the Jefferson River and Gallatin River to form the Missouri River.