The short answer
Global weather models are skilful out to about a week for the broad pattern, whether it will be cold or mild, settled or stormy. Snowfall at one resort is harder, because it depends on exactly where a front stalls and how cold the air is at that hour, and those details are only reliable a few days ahead. As a working rule:
- Days 1 to 3: trust the timing and the amounts, within the range shown.
- Days 4 to 7: trust that a storm is coming; expect the day and the amount to shift.
- Days 8 to 14: trust the pattern, such as “a cold, unsettled spell arrives late next week”. Do not book around a number.
Why amounts are the weak point
To forecast that 30 cm will fall on a particular mountain, a model has to get the storm track, its speed, the moisture in it, the temperature at every height and the effect of the mountains themselves all right at once. Each of those has some error, and the errors multiply. That is why snowingplaces shows snowfall as a range from three models rather than one number: if the three disagree, the forecast is telling you something.
Why the models disagree more the further out you go
The atmosphere is chaotic: tiny differences in the starting point grow into big differences in the outcome. Models start from slightly different pictures of today’s weather and use different maths, so their forecasts diverge with time. When all three agree on a storm five days out, that agreement is itself evidence. When one says 40 cm and another says 5 cm, the honest answer is that nobody knows yet.
How snowingplaces handles this
Days 1 to 7 use three models, and each day says how many of them show snow. Days 8 to 14 use two, because the ICON model stops at about eight days, and that section is labelled an outlook rather than a forecast. Every forecast is rebuilt every three hours with the models’ newest runs, so the closer you get to the day, the better the forecast on the page.
The practical rule
Book the trip on the season’s record and the resort’s altitude. Watch the 14-day outlook for the pattern. Decide which day to ski on the 3-day forecast. And check the morning of, because the last update is always the best one.