Question

Generally when do glaciers advance downward, causing further erosional landforms?

Is it in the colder months like in November and December or all year long?

Answer 1

The answer is "During the times of excess precipitation in the form of snow"

Hope this helps

Answer 2

During colder months the snowfall is high and that's when it accumulates turning into ice and forming glaciers.

Glaciers move by the pressure of its own weight and the gravity force.

They move by the internal deformation of the ice, the deformation happens when thw mass or weight of a glacier spread out due to gavity.