The short answer
Interior BC snow is cold and dry because storms wring most of their moisture out crossing the coast ranges before they reach the interior, then drop light snow at elevation through a long, steady cycle of systems. Skiers call the result cold smoke: snow light enough that it barely holds together. It stays good between storms because the treed terrain shelters it from sun and wind. That is the whole reason a refill day works here.
Where the light snow comes from
Cold smoke, explained plainly
The coast gets enormous snowfall, but it is heavy and wet because the air coming off the ocean is warm and loaded with moisture. As those systems push inland and climb over the coast ranges, they drop most of that moisture on the way. By the time the air reaches the interior it is colder and drier, so the snow that falls is lighter and holds less water.
This is the continental-maritime transition: the interior sits far enough from the ocean to be cold and continental, but close enough to still catch the storms. Add elevation, which keeps temperatures low, and you get snow that falls cold and stays cold. Light, dry snow is simply snow with a lot of air in it, and that air is what makes it feel bottomless underfoot.
Why it stays good between storms
Cold snow has two enemies once it is on the ground: sun and wind. Both of them pack it down and turn it stiff. The advantage of interior terrain is the trees. Fir and spruce glades shade the snow from the sun and break up the wind, so the cold snow underneath keeps its quality for days after a storm has passed.
This is why a place can ski well on a clear day three days after the last snowfall, as long as you know which aspects and which stands of trees held their snow. On open, wind-exposed terrain that same snow would have gone stiff by now. In the sheltered glades it is still soft.
The rhythm of a good week
What a refill day means
A refill day trades on all of the above. Because the treed terrain holds cold snow between storms, an operation with a whole tenure and few guests never has to ski out its best snow in one go. On a thinner stretch of weather, the day moves to the terrain that is still holding, skis it gently, and lets the rest recover until the next system moves in.
The result is a week that stays good to the end instead of peaking on the first bluebird morning. It is less about chasing storms and more about managing the snow you already have, which is a luxury that only exists where there is no lift line above you competing for the same lines.
An honest note on the numbers
Powderhorn Basin is a concept build, so the specific snowfall figures and season details on this site are illustrative of how an interior BC operation works, not measurements from a real snow record. The physics in this guide is real. The particular numbers are drawn to be plausible for the region, and on a live operation they would be the actual record, posted and updated as the season runs.