Does snowmaking guarantee an opening?

No, and this index cannot tell you how close it gets. The weather reanalysis behind every score here knows about the sky and nothing at all about snow guns. That exclusion is deliberate, and this page is the scope statement for it: what is modelled, what is not, and what a low score therefore does and does not mean.

Why snowmaking is left out rather than estimated

Because estimating it would make the comparison worse, not better. A resort's real snowmaking capability is a function of installed gun count and type, pipe and hydrant coverage across specific runs, water rights and reservoir volume, pumping capacity, overnight operating hours and how much of that gets used in a given autumn. Almost none of it is published in a form that is comparable between two resorts, let alone between 53 of them in 26 countries. Modelling it for the resorts that disclose and guessing for the rest would quietly reward disclosure and punish silence, which is not a measurement.

So the index does the one thing it can do identically everywhere: it reads the same weather model at every destination with the same rules and reports what the atmosphere put on the ground. Everything else is named as excluded rather than approximated.

What a zero actually means

13 destinations scored zero: not one of the last 10 opening weeks reached 30 cm12 in on 3 days. They are in 11 countries and their model cells run from 297 m974 ft at Levi to 3793 m12444 ft at Breckenridge, so this is not a list of low resorts. Several of them open on schedule every single year and ski well when they do.

A zero says the sky did not do the work in that week. It does not say the lifts did not turn, that the skiing was bad, or that the resort misled anyone. Read against a destination's own record it is a useful warning about the early season specifically: a mountain that has never had a natural base at opening is a mountain whose first weeks depend entirely on what it can make and hold, and on what falls between the opening and your arrival.

The one thing the weather does say about snowmaking

Guns need cold. Snowmaking depends on the wet-bulb temperature being low enough for a water droplet to freeze before it lands, which is why a mild, damp autumn shuts the guns down at the same time as it fails to deliver natural snow. The two failures are correlated because they have a shared cause. This index does not model that either, and it is not claiming a number for it, but it is the reason to treat a warm forecast in the week before an early trip as a double warning rather than a single one.

Where to get the real answer before you travel

From the resort, and from the sky, separately. The resort's own snow report is the only source for lift status, open terrain and measured base depth, and it knows things no model can. Treat it as informed and interested at once. For the independent half, the live board shows where it is actually snowing right now, each destination file reads the model at that mountain's own summit elevation, and the Ski Meter scores today with every point of its working shown.

The historical half of the picture is the index, and the rest of these answers are in the question index.