Very little of that precipitation, however, is reaching the valley floor (although it's beginning to get close as I write this). It's mostly snow that is falling and sublimating (when ice turns directly into vapor) before it reaches the ground.
The reason that this precipitation shows up on radar is that the beam originates on a mountain peak (Promontory Point) and is oriented with a slight tilt relative to the horizon (0.5º). The starting elevation, combined with the slight tilt and curvature of the Earth, overwhelms the slight tendency of the atmosphere to bend the beam back towards the Earth's surface. As a result, the KMTX radar samples the atmosphere well above the valley floor, meaning it sees the snow aloft rather than what's happening at lower levels.
|Source: Secrets of the Greatest Snow on Earth|