Read the snow numbers
Snow-to-liquid ratio: why some storms ski deeper than others
What snow-to-liquid ratio means, why 10:1 is only a reference point, how temperature, humidity and wind change it, and how SkiBuds estimates it for a forecast.
By SkiBuds · Updated
Snow-to-liquid ratio (SLR) is how many inches of snow fall for each inch of liquid water. At 10:1, an inch of water makes ten inches of snow; at 20:1 the same inch of water makes twenty inches of much lighter snow. The ratio is the main reason two storms with the same amount of water can ski completely differently, and temperature in the cloud is the biggest single influence on it.
Why 10:1 is only a reference point
Ten to one is a convenient rule of thumb, not a constant. Wet snow near freezing can settle around 6:1 to 10:1. Light, cold powder can run well above 15:1, and some cold, dry storms in the mountain West go higher still. Forecasts that convert water to snow with a fixed 10:1 will underestimate a cold storm and overestimate a warm one.
That is also why snowfall and snow water equivalent are different numbers. Snow depth vs snowfall vs SWE explains how each measurement is reported.
How temperature shapes the ratio
Snowflakes grow differently at different temperatures. The large, branching crystals called dendrites form best roughly between 0 and 10 °F (about -18 to -12 °C). They stack loosely with a lot of air between them, so they produce the highest ratios. Warmer than that, flakes are wetter and pack down. In very cold, arctic air, crystals tend to be small plates and columns that pack more tightly, so the ratio falls again.
The SkiBuds app's forecast uses a temperature curve with that shape as its starting point:
| Temperature | Starting ratio |
|---|---|
| 32 °F or warmer | 10:1 |
| 20 °F | 16:1 |
| 10 °F | 21:1 |
| 5 °F | 23.5:1 (the peak) |
| -20 °F or colder | 9:1 |
Between those points the ratio changes smoothly: it rises half a point for every degree colder down to 5 °F, then falls back toward 9:1 in arctic air.
What else moves the ratio
Temperature is a starting point, not the whole answer. The app adjusts each snowing hour for three more conditions:
- Humidity. Drier air raises the ratio and moist air lowers it. Relative humidity of 70% leaves the estimate unchanged; 50% adds 1.5 points, and 90% takes 1.5 away.
- Wind. Wind breaks crystals apart and packs them as they land, so the stronger the wind, the lower the ratio, by up to two points.
- Heavy snowfall rates. When precipitation is falling very hard, the estimate drops by a point, because fast-falling snow compacts under its own weight.
Every hour is then held between 6:1 and 30:1. Wet, dense snow rarely settles much below 6:1, and cold intermountain storms can legitimately reach 25:1 to 30:1.
To compare mountains at different heights fairly, the app can also adjust a temperature reading to a common reference of 9,000 feet, using a standard rate of 3.5 °F per 1,000 feet. A valley sensor and a summit sensor are then scored on equal terms.
Why a storm total is weighted by snowfall
A storm's overall ratio is not the average of its hourly ratios. One fluffy hour that drops six inches matters more than six damp hours that drop a trace. SkiBuds counts only the hours when snow is actually falling and divides total snowfall by the estimated total water, so dry hours do not drag the number toward wet-snow values.
What the numbers feel like on the hill
The app attaches a plain-language label to each hourly ratio:
| Ratio | Label |
|---|---|
| Above 20:1 | Champagne powder |
| Above 17:1 to 20:1 | Blower powder |
| Above 15:1 to 17:1 | Cold powder |
| Above 13:1 to 15:1 | Powder |
| Above 12:1 to 13:1 | Light and dry |
| Above 11:1 to 12:1 | Dry |
| Above 10:1 to 11:1 | Average |
| Above 8:1 to 10:1 | Moist |
| Above 6:1 to 8:1 | Wet snow |
| 6:1 | Heavy and wet |
High ratios float you and fill tracks quickly, but they offer less coverage over rocks for the same water. Dense, low-ratio snow builds a base, holds up under traffic and can be heavy to ride when it is deep.
How to use it when planning with friends
- Compare water and ratio, not just inches. Ten inches at 8:1 holds more than twice the water of ten inches at 20:1 and will ride very differently.
- Look at when the cold arrives. Storms often start warm and finish cold. Light snow falling on a denser layer can make for a good first morning.
- Treat it as an estimate. The ratio comes from forecast temperature, humidity, wind and snowfall, not a measurement of the snow. Temperature alone is a weak predictor in the mountains, so check observed snowfall and the resort's report before you commit.
How to read a ski resort snow forecast covers timing and elevation, and planning a powder day with friends turns the forecast into a meeting time. Each mountain in the resort directory has its own forecast page on this website. The estimated snow-to-liquid ratio described here is part of the SkiBuds app, which is being rebuilt for iOS and Android and is coming soon.