# Snow depth vs snowfall: which number helps plan your ski day?

> Snow depth vs snowfall vs SWE: what each measures, why 8 inches (20 cm) of new snow can raise depth by only 4, and which to compare.

Source: https://skibudsapp.com/guides/snow-depth-vs-snowfall
Updated: 2026-11-06

A storm can drop 8 inches (20 cm) of new snow and raise the snow stake by only 4 (10 cm), and both numbers can be right. Snowfall is how much new snow fell over a stated period. Snow depth is how much snow is on the ground right now at one spot. Snow water equivalent (SWE) is how much water that snow would melt into. The gap between the first two comes from how they're measured: new snow settles from the moment it lands, and National Weather Service observers can add up as many as four six-hour snowfall readings to make one daily total. For a ski day, compare new snowfall over the same hours to find fresh snow, and use depth to judge coverage.

## Three numbers answer three different questions

| Number | What it describes | How to use it |
| --- | --- | --- |
| New snowfall | Snow that falls over a stated period | Compare the same period, and tell a forecast from an observed report. |
| Snow depth | All the snow on the ground at one measurement point | Check where and when it was measured before treating it as mountain-wide coverage. |
| Snow water equivalent (SWE) | The water the snowpack would melt into | Read it as water content; it is neither snow depth nor fresh snowfall. |

A mountain can report a deep base while expecting little new snow, and a storm can bring a foot of snowfall while the depth stake rises by much less. Before your group compares mountains, agree on the question: fresh snow, existing coverage, or the water stored in the snowpack.

## Why 8 inches of new snow can raise the depth by only 4

The [NWS snow measurement guidelines](https://www.weather.gov/gsp/snow) explain most of the gap, because the two numbers are measured in different ways. Snowfall is read from a snowboard, a flat white board set on the snow. The observer records "the greatest amount of snowfall that has accumulated" on it, clears it no more than once every six hours, and is told to "never sum more than four, six-hourly observations" for a 24-hour total. The reason is in the next sentence: using more than four "would falsely increase snowfall totals." The rule-writers know that measuring more often makes the number bigger, so they cap it. Snow depth is measured once a day at the scheduled observation time, by reading a fixed snow stake or averaging several measuring-stick readings of all the snow on the ground, old and new, rounded to the nearest whole inch.

Here is a **hypothetical** storm day measured that way, with a 6 a.m. observation time. The observer reads the board at noon, 6 p.m., midnight and 6 a.m. and finds 3, 2, 2 and 1 inches. Snowfall for the day: 8 inches. The depth stake read 40 inches at 6 a.m. yesterday and reads 44 inches at 6 a.m. today. Both numbers are correct.

Each board reading catches snow within six hours of landing, before it has had long to settle. The snow on the ground has been settling the whole time. Researchers at Saint Louis University who studied 30 years of NWS snow records note that "considerable increases in snow density can take place within a 24-h period" as the crystals change shape and pack down ([Baxter, Graves and Moore, 2005](https://www.eas.slu.edu/CIPS/PUBLICATIONS/Baxter2005.pdf)). Denser snow takes up less height.

Melting can widen the gap until the depth gains nothing at all. The NWS page gives the example of three snow squalls of 3.0, 2.2 and 1.5 inches, each melting before the next arrives. The day's snowfall is 6.7 inches, "even though the snow depth on your board at observation time was zero." Wind moves snow off one spot and onto another, which is why a single stake can miss what fell nearby.

A gap between a resort's snowfall total and the rise in its reported depth does not establish that either figure is wrong. The NWS rules describe how its observers measure; a resort's report is its own measurement. Check the location, reporting period and method before comparing them.

## SWE tells you how much the snow weighs

Snow water equivalent is the depth of water you would have if the snow at a measurement point melted. Ten inches of snow that melts to one inch of water has an SWE of one inch, a 10:1 snow-to-water ratio. [Avalanche.org](https://avalanche.org/avalanche-encyclopedia/weather/snow-ratio/) puts a reasonable average near 12:1, wet "Sierra cement" around 5:1, and the lightest powder as high as 30:1, so two storms with the same SWE can leave very different depths. [Snow-to-liquid ratio explained](https://skibudsapp.com/guides/snow-to-liquid-ratio) shows how temperature and wind change it.

The [USDA NRCS SNOTEL network](https://www.nrcs.usda.gov/resources/data-and-reports/snow-and-water-interactive-map) measures SWE automatically at more than 800 sites in remote, high-elevation watersheds of the western US. [NOAA's drought portal](https://www.drought.gov/data-maps-tools/snow-telemetry-snotel-snow-depth-and-snow-water-equivalent-products) describes how: a snow pillow at each station "measures how much water is in the snowpack by weighing the snow." Weighing sidesteps two of the problems above. Settling doesn't change weight, so snow that packs down from 8 inches to 4 weighs what it did when it landed, and a pillow has no board for anyone to clear.

A nearby SNOTEL station gives useful context about water in the snowpack at that station. It does not directly verify a resort's snowfall total: the sites may receive different precipitation, sit at different elevations, or report over different periods. Wind, rain and melt can affect the change in SWE too. Read the station and resort reports as separate observations, and check their locations and times before comparing them.

## Every snow number needs three labels: what, where and when

The measurement rules point to the fix. A snow number means something only when it carries three labels. **What:** new snow, base depth or SWE, and forecast or measured. **Where:** which station, stake or elevation, since a summit forecast and a mid-mountain stake describe different snow. **When:** which hours it covers and when it was issued or read. "The mountain has 12 inches" carries none of them, and it could mean new snow, base depth or a forecast. When you open a [resort forecast](https://skibudsapp.com/resorts), note its source, location and update time, and check terrain and lift openings with the resort itself, because snow totals don't tell you which runs will open.

Here is an **example** message with made-up numbers for [Crystal Mountain](https://skibudsapp.com/resorts/crystal-mountain):

> Saturday at Crystal: forecast 6 in. new snow in the 12 hours ending 6 a.m. (NWS, updated Thu 3 p.m.). Base depth 52 in. at the mid-mountain stake (resort report, Thu 7 a.m.). Recheck Fri 6 p.m. If it holds, we leave at 6:30 and meet at the base lodge.

Every number in it says what it is, where it came from and when. The [powder-day group plan](https://skibudsapp.com/guides/plan-a-powder-day-with-friends) turns a check like this into a meeting time, and the [official weather, road and avalanche resources](https://skibudsapp.com/resources) cover the parts of the trip a snow number can't answer.

The labels earn their keep on Friday at 6 p.m. Say the update cuts the forecast to 2 inches. Nobody has to ask which number changed: the new-snow forecast went from 6 to 2, the 52-inch base didn't move, and the group can decide in one message whether 2 inches on a deep base is still worth a 6:30 start.