Why does snow seem lighter right after it snows?

Answer 1

You're correct that it is lighter immediately after it falls. If you look closely at snowflakes as they fall and accumulate on top of each other, you'll notice that there is often a lot of space between them. In fact, a snowpack can primarily be air rather than ice crystals after it first falls!

But over time, the snow will "settle", basically meaning that it will compact under its own weight. Obviously this factor is more significant the more snow you have piled up. How "light" the snow is will also depend on its snow/water ratio, which often varies considerably. An inch of snow that melts into .25 inches of water is like cement, but a very fluffy inch of snow might melt into only 0.05 inches of water.

Then when the temperature warms above freezing or the sun comes out, snow on top will melt, and the melt water will percolate through the snowpack, often freezing again and making the snow even denser and heavier. As you have probably noticed, the last of a melting snowpack is often a mix of crunchy snow and a sheet of pure ice. The snowflakes that originally comprised the layer of snow have long been either melted or metamorphosed.

Answer 2

Freshly fallen snow can seem lighter right after it snows because the snowflakes are less compacted and have more air pockets between them, creating a fluffy texture. As the snow settles and compacts over time, it becomes denser and heavier.