NOAA just referred to the lake as relatively warm .."
.A NORTH FLOW OF ARCTIC AIR MOVING ACROSS THE RELATIVELY WARM WATERS
OF LAKE SUPERIOR WILL CONTINUE TO PRODUCE LAKE EFFECT SNOW SHOWERS IN
THE SNOW BELTS EAST OF MARQUETTE AND THE SNOW BELTS OF FAR WESTERN
UPPER MICHIGAN THROUGH THURSDAY"
They are referring to the water being warm relative to the arctic air moving over it. Not the water temp itself which I would guess is about 33-34 degrees f.