Here is a working prototype ice/snow sensor. It is intended to mount in an electrical utility box type enclosure that is placed in the concrete of a sidewalk or driveway. When snow is detected, this unit signals a control box that turns on electrical heating cable embedded in the concrete.
The top measures just under 4 inches in diameter. Printed of ABS on my SeeMe H-1.1 The two rails on the top are brass rods used as electrodes to detect the snow or ice.
Inside the lower body is a circuit board with a PIC microprocessor that runs the sensor. Laying out that board in such a small space was a real treat!
This unit will spend the winter outside, being monitored for how well it responds to real world ice and snow conditions.