The weather process that produces snow in the Rocky Mountains is orographic lift. Here's how it works:

1. Moisture-laden air: The Rocky Mountains act as a barrier to prevailing winds carrying moisture from the Pacific Ocean.

2. Forced ascent: As the air encounters the mountains, it is forced to rise.

3. Cooling and condensation: As the air rises, it cools due to lower atmospheric pressure at higher altitudes. This cooling causes the water vapor in the air to condense, forming clouds.

4. Freezing: If the temperature drops below freezing (0°C or 32°F), the water droplets in the clouds will freeze, forming ice crystals.

5. Snowfall: These ice crystals grow larger and heavier, eventually falling to the ground as snow.

In summary: The Rocky Mountains' elevation causes air to rise, cool, and condense, leading to the formation of snow.