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Snowpack

Know the Mountain

We rebuild the mountain you are standing on from its own survey, and put the day's weather, the avalanche danger and the ski patrol on it. In a browser. Before you get off the lift.

Open the app Pro

The mountain itself

Lidar elevation and surveyed geometry, built into real terrain on your device as the page opens. Every run, lift, building and tree stands where it stands in the ground truth.

The sky it is under

Live snow and weather read band by band up the hill, with the hour by hour ahead, so the summit and the base are two different answers because they always were.

What to do if it goes wrong

Avalanche danger by aspect and elevation, the ski patrol line for the mountain you are on, and an SOS that sends where you are. None of it is behind a price.

Built from surveyLidar elevation and mapped geometry, built at load time on your device.
Safety is freeAvalanche danger, patrol and SOS are always free.
Nothing to installIt runs in the browser on a phone, a laptop or a headset.
Every number is sourcedMeasured, reported or modelled, labelled on screen.

What Snowpack does

Lidar-mapped mountains Every mountain rebuilt from its own survey on lidar elevation. Every run, lift and building where it really stands. Ski it or ride it Ski or snowboard the mountain in first person, on physics solved from your own height and weight. Board twelve kinds of lift. Your skiing, measured Runs, vertical, distance, top speed and the time you spent skiing rather than riding, kept on your own device. Live weather and snow The sky, the snow surface and the storm are the hour you are in: cloud base, snowfall rate and wind on the forecast bearing. Where the snow is Every mountain ranked by new snow, base and what is coming, measured at its station and modelled at its own coordinate, labelled either way, tracked over the season. Patrol, danger and SOS Avalanche danger by aspect and elevation, ski patrol lines verified against the resort own page, and a hold-to-arm SOS. Always free. Live trail GPS and maps Where you are on the mountain, which way is down from here, and the trail map drawn from the same survey. Headsets, visors, glasses The same mountain on a phone, a laptop, a VR headset or smart glasses. Nothing to install anywhere. Your group, no accounts Share where you are with the people you came with, end to end encrypted, on a four-word phrase and nothing else. Every number is sourced Measured, reported or modelled, labelled on screen, with the station or bulletin it came from and when it was read.

Open a mountain See the price

A skier off a cornice with the sun behind them

01 · The day

The day, measured on your phone

The app counts the day from your phone's own position fixes: runs, vertical, distance, top speed, and the time split between skiing, riding lifts and standing still. The calculation runs on the device. Position fixes stay on the device.

What counts as a run A descent is counted as a run once it covers 390 feet of ground and drops 82 feet. It closes when you board a lift or stop moving for 75 seconds. The thresholds are fixed and identical at every mountain, and a traverse to a lift line does not meet them.
Every run split out Vertical, distance, duration and top speed are recorded for each descent. The day is stored under the mountain and the date and written every five seconds, so a break, a flat battery or a page reload does not lose the morning.
Lift time separated from ski time Lift riding is detected by comparing your track against the surveyed lift line and your speed against that lift's rated speed. Time on a lift and time stopped are counted separately from time skiing.
What is kept, and for how long The per-descent record is held for the day and then cleared. The day's totals roll into a season ledger that is kept: days out, mountains, runs, vertical, distance and top speed, per season and across every season on the device. The season runs 1 August to 1 August.
Where it is shown Live in the legend while you ski, on the instrument layer in first person, and on your profile as per-day charts, per-mountain totals and the table of every recorded day.

Your season

A record of your skiing

Each day's totals are added to a season ledger and kept: days out, mountains skied, runs, vertical, distance and top speed, for the current winter and every winter recorded before it. The season boundary is 1 August, so a January day is counted in the winter it falls in.

The profile shows the career figures, the season figures, per-day charts for vertical, runs, top speed and time split, a cumulative chart against the previous season, a card per mountain with its own totals and dates, and the table of every recorded day.

You give it four measurements, and only because the model uses them. Your height and weight decide how much air you push, so a tuck is worth what a tuck is worth for your body. Your ski or board length and its waist width decide the arc you carve. Pair a heart rate monitor and your pulse rides along with the day.

Season after season, on this device
Synced only if you say so
Raw positions stay on the phone

Open your profile

02 · How it is built

Built from measurement

Every surface is built at load time from elevation data and surveyed geometry, in the browser, and is checked against surveyed summit elevations after it is built.

The elevation chain

The shape of the mountain comes from a digital elevation model served as map tiles. Inside the United States the first request goes to USGS 3DEP lidar, the national airborne laser survey, at a nominal 3 feet. Outside it, and anywhere 3DEP has not flown, the chain falls back to a global elevation survey at about 100 feet.

The chain is declared in one file that both the browser and the tile route read, so the resolution the app asks for is always one the route serves. The source that built the terrain in front of you is named on screen with its nominal resolution.

The heightfield is meshed at 320 segments a side, about 205,000 triangles, and the mesh density drops on a device that misses the frame budget. Terrain quads run 62 to 203 feet, median 126 feet.

The geometry

Runs, lifts, buildings, roads, forest stands, water, car parks, peaks and named places come from open mapping data, baked once per mountain and shipped with the app so the mountain loads with no network round trip.

The survey radius is 3.7 miles, which in a shared canyon reaches neighbouring areas. Runs, lifts and station markers are clipped to the resort's own winter sports permit boundary plus an 820 foot margin for access runs. At Solitude that removes 483 runs belonging to Brighton and Park City. The clip applies at every mountain whose boundary the survey carries.

Lifts are built as machines: towers at surveyed positions, rope height and sag from the machine type, drive and return terminals, a maze, carriers at the spacing that type runs, and cabin doors on a cam profile with a dwell time. Twelve lift types are modelled, from fixed-grip chairs to chondolas, T-bars, platters, rope tows and magic carpets.

The light and the snow

The sky is computed from Rayleigh and Mie scattering for the sun angle at that place and minute, so horizon paling and sunset reddening follow from the air mass along the line of sight.

Snow is shaded from published measurements of snow albedo, grain size and subsurface scattering, held in a module a test can read without a GPU.

Sun and moon are placed at their computed altitude and azimuth for the coordinate and minute, at their true angular size, with the moon's phase. After dark the stars brighter than magnitude 2.0 and the naked-eye planets are drawn at their computed positions from J2000 elements.

3 ftLidar, where flown

205kTerrain triangles

Surveyed runs drawn on the mountain — **Runs on the real slope**Each line sits on the elevation model, so a trail that traverses a bench looks like a traverse.

The base village built from surveyed footprints — **The village from its footprints**Outlines are surveyed. The roof, the pitch and the material come from the regional building style.

The mountain after dark — **Night, computed**Moon position and phase, star field and lit windows, for that coordinate at that minute.

Medium USGS 3DEP lidar at 3 ft, global 100 ft elevation elsewhereMesh 320 segments a side, about 205,000 trianglesCheck against surveyed summit elevations, after the build

03 · First person

Stand on it before you drive there

A first-person camera at eye height on the same geometry the map is drawn from. Walk the base area, board a lift, ride it to the top station and ski down.

Walk it at eye height The camera sits 5 feet 7 inches above the surface and is clamped to the loaded terrain. Building footprints are collision geometry, and the spawn point is checked against them.
Ride the lifts, all of them Fixed-grip and detachable chairs, gondolas, aerial trams, chondolas, T-bars, J-bars, platters, rope tows and magic carpets. Enter the maze, board at the terminal, ride the line and step off at the top station. Cabin doors open on a cam profile at the terminal and hold for a dwell time set by the machine type. 12 lift types modelled
Ski it with real physics The descent is solved from your entered height and weight, the pitch under the skis, the snow friction coefficient and air density at that altitude. Every coefficient is a measured value with a cited source. The model is checked against a published figure: a 5 foot 10, 176 pound skier tucked on a 25 degree groomed pitch at 8,200 feet reaches 62 to 75 mph.
Read the signs Every board carries a name, a difficulty symbol and a direction taken from the survey for that resort. Junction boards carry a trail map with the sign's own position marked.
Three cameras, one simulation Eye, chase and overhead are framings of one simulated rider. The physics is identical in all three; the camera is a separate object that observes it.

First person on a run — **On the run**Eye height, the run under you, the instruments on the view.

Riding a chairlift — **On the lift**Board it, ride it, and get off at the top station.

The mountain as a tabletop model — **On the table**The whole mountain shrunk to a model you can walk around in a headset.

A snowboarder off a park jump above a treed ridge

04 · Where you are

Where you are, and which way to go

Position, heading, the runs leading away from where you stand, the trail map, and the route to any point you pick.

Which way is down, from here Runs within 850 feet of your position are listed with their name, difficulty and the direction to start. Forward is decided by elevation: the direction that descends. The bearing is taken over the first stretch of the run.
Directions against the way you face Directions are given relative to the way you are facing. Heading is taken from the magnetometer when you are stopped and from your track when you are moving, blended between the two, so it works both standing at a junction and skiing.
Your position on the mountain A figure on the snow at your fix, facing your heading, with a ring showing the reported accuracy. Its state is one of on a run, riding a lift, or stopped: on a run means within half a trail width of a run centreline, riding a lift means your track matches a lift line and your speed matches that lift's rated speed.
The trail map, from the survey An aerial map from anywhere in the app, with full zoom, or pinned as a small preview while you ski. It is vector, drawn from the same survey the mountain is built from, and works with no network.
Drop a pin anywhere, and go Press any point, building or lift station for its name, what it is, and a route. The route is drawn on the snow in orange. In first person, pressing a structure returns the same detail.
Every mountain on one map The world map is shaded relief rendered from the same elevation tiles the 3D mountain uses, served from our own route. Resorts are clustered on the GPU, so the marker count does not affect panning.

Sixty-three mountains, at their true coordinates

Fifty-two in the United States, eleven in Canada. Each one is a baked survey on disk.

A surveyed mountain Shaded relief from our own elevation tiles State and country lines from our own boundaries route

A snowboarder dropping off a rock band on a steep slope

05 · Safety

Avalanche danger, patrol, and the call for help

Avalanche danger by aspect and elevation, active weather warnings in full, ski patrol contact and posts, and a hold-to-send distress signal. Every item in this section is in the free version.

Avalanche danger, by aspect and elevation

The reading is a grid of eight compass aspects by three elevation bands: below treeline, treeline and alpine. Each cell carries its own rating on the five-step North American Avalanche Danger Scale, in that scale's own colours. This is the standard operational display used by avalanche centres, ski patrol and guides.

Rings run from below treeline at the centre to alpine at the outside. Each wedge is one of the eight compass aspects. A north-east facing slope in the alpine band reads off one cell. The five ratings and their colours are set by the North American Avalanche Danger Scale.

The app also shows the bulletin's problem types, its valid period, and the forecast zone the reading was issued for.

Which forecast the reading comes from The bulletin is resolved for the avalanche forecast zone the coordinate falls inside. Where a second centre publishes for the same ground, both readings are shown with the issuing zone named on each.
Weather warnings, in full Active warnings, watches and advisories for the coordinate are shown with their complete text, their event type and their valid period. Severe alerts can be spoken aloud. Alerts are shown on every tier.
The ski patrol register Every one of the 63 mountains has an entry: the patrol's emergency line, alternate numbers or the medical desk where the resort lists one, the patrol posts, and the procedure that resort publishes for an injured guest. Each number carries the page it was read from and the date it was read. Last verified 2026-09-02
How a number gets on screen A number is shown only after the verifier fetched the resort's own page and matched those digits on it. A number reaches the screen once that match succeeds. Where nothing was confirmed, the screen shows 911 and directs you to the nearest lift attendant, who radios patrol. Emergency services are shown at every mountain, above any resort line.
Where the posts are drawn A patrol post is placed on the mountain when it resolves to surveyed geometry: a lift terminal, a named building, or a surveyed patrol place. Where the survey has no geometry for it, the post is listed by name with the resort's own description of where it stands. The nearest post is given with its distance and bearing.
SOS: what pressing it does Hold the control for three seconds to arm it. Your position and an SOS flag are written into the encrypted packet your group already receives, and the position is refreshed as you move. Where the resort has enrolled a patrol room, the same position is sent there on a separate channel, and a patroller can acknowledge it back to your screen.
What the screen tells you while it is armed The distress line reports its actual state: armed, sent, delivered, or acknowledged by a named patroller, each with its own wording. Where the resort has not enrolled, the screen says the signal reaches your group only. 911 is shown in every state.
The patrol side An enrolled patrol room opens a board that lists armed signals with position, elevation, the nearest surveyed place name, time since arming, and a control to acknowledge. It is served under a key issued to that room and carries noindex.

The avalanche rose in the app — **The rose in the app**Aspect by elevation, on the mountain it belongs to.

Group members on the mountain — **Your group, live**Where everybody is, and the hold control that raises SOS.

06 · Your people

Your group on the mountain, with no accounts

A group is identified by a four-word phrase. The encryption key and the mailbox name are both derived from that phrase on the device.

How the encryption works

The phrase is stretched with PBKDF2 into an AES-GCM key, and hashed with SHA-256 into the mailbox name. Neither the phrase nor the key is transmitted. The relay stores ciphertext under a hashed name and discards it after two minutes.

Membership is possession of the phrase. There are no accounts and no server-side roster.

How sharing starts and stops

Sharing begins on a button press. While it is running a persistent chip is shown that doubles as the stop control. It stops when the tab closes and does not resume on return.

What is carried

Position, heading, speed, battery level, and the day's run, vertical and speed summary where you have switched that on. Each packet carries the current fix only.

Members appear on the 3D mountain as beacons with name and distance, and in a roster with last-seen times. An armed SOS flag travels in the same packet.

Medium AES-GCM over a relay that holds ciphertext onlyKey PBKDF2 from a four-word phrase, on the deviceRetention two minutes

07 · Where it runs

A phone, a laptop, a headset or glasses

One web application, no install and no app store. The same scene and the same figures on every device it runs on.

PhoneSplit thumb zones: the left side steers, the right looks. The frame time is measured every frame and quality is reduced in a fixed order (resolution scale first, then shadows, trees and particles) to hold the target frame rate. Add to Home Screen installs it as a standalone app.
HeadsetWebXR immersive-vr, with the button shown only where the device answers for that session type. Trigger to glide, snap-turn, and a stick press to switch between full scale and a tabletop model, about six and a half feet across, that you walk around.
Glasses and assistive inputVoice commands drive the instrument layer where the browser exposes speech recognition. Dwell select activates any control by resting a gaze or head pointer on it for a set time. Both are off by default and are switched on in the command centre.
BatteryRendering stops when the tab is hidden. Pixel ratio and shadow map size are capped on phones, and a saver mode lowers the frame target and disables particles.

The instrument layer as seen inside a headset

The instrument layer: speed, elevation, vertical, heading, the run you are on and the named places around you, in ruled strips with the centre of the frame kept clear. Every figure is the same one the legend and the card show. Feet, miles and miles per hour. Press V to fold it away.

Medium One web application, WebGL and WebXRSurfaces phone, laptop, headset, glassesInstall Add to Home Screen

08 · Price

Free to use. Pro is $3.99, once

One payment, kept for good, including every mountain added after you buy. The API plan is for people building their own product on the same engine.

The one-time price holds for the first 100,000 accounts. After that Pro becomes a subscription. Anyone who buys before then keeps lifetime access, including every mountain added later.

Free

forever

All 63 mountains, built from survey and elevation data
Avalanche danger by aspect and elevation, on the North American scale
The bulletin's problem types, valid period and forecast zone
Active weather warnings with their complete text
Ski patrol line, alternates, posts and the resort's own procedure
Nearest patrol post with distance and bearing
Hold for SOS, with your position sent to patrol where the resort has enrolled
911 and the lift-attendant fallback, at every mountain
Current temperature, wind, new snow and base depth
Seven-day forecast, and the next hour of precipitation
Vector trail map, drawn from the survey, works offline
World map of every mountain, on our own elevation tiles
Orbit, pan and overview zoom on the 3D mountain
Sun, moon, phase and the night sky, computed for the minute
Feet, inches, miles and mph throughout
No account and no payment details
Close zoom, first person and VR are Pro
Live weather in the 3D scene is Pro
Station readings and band forecasts are Pro
The measured day and the season ledger are Pro
Sharing your live position with friends is Pro

Open the free version

Founders · lifetime · first 100k

Pro

$3.99 once

lifetime, at the founders' price

Everything in Free
Close zoom to the door, the deck, the lamp and the kerbstone
First person at eye height: walk, board lifts, ride and ski
Ski physics solved from your height, weight, ski length and waist
Eye, chase and overhead cameras on one simulated rider
WebXR headset mode, and the tabletop model you walk around
The measured day: runs, vertical, distance, top speed, time split
The season ledger, kept season after season
Profile desk: career and season figures, per-day charts, personal bests, a card per mountain and the table of every day
End-to-end encrypted group link, roster and live beacons
Severe alerts spoken aloud
Station readings band by band, with elevation and reading time
Live weather in the scene: cloud base at the forecast altitude, snowfall at the forecast rate, wind on the forecast bearing
Night: moon phase, planets and stars at computed positions
Voice commands and dwell select on the instrument layer
Spoken mountain brief, on request
Battery saver and the adaptive frame governor
The full snow tracker: every mountain, every state, thirty days of history and the chart
Search any place from the weather card on the front page
Every mountain added later, at no extra cost

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Or pay in USDC over x402 Machine payments on the open HTTP 402 standard: an agent signs one transfer and gets the same lifetime key, with no account and no card. POST /api/x402 with {"buy":"pro"}. How it works

Save as file

This is your lifetime key. It is saved on this device and works on any other device via Restore. Keep a copy. Open the app

API

$5.99 / month

for builders, cancel any time

/api/atlas by coordinate or by slippy tile
Avalanche danger by elevation band, with the issuing zone
Active alerts with event type, full text and valid period
Land ownership and boundary beneath the point
The nearest reporting instrument and its reading
/api/dem, /api/features, /api/conditions and /api/boundaries are open to everyone, key or no key: elevation tiles with lidar where flown, surveyed runs, lifts, buildings and forest, the reconciled weather feed and the permit polygons. They are listed here because they are part of the API, not because the key is what opens them
Edge cached per tile, so a repeat call costs nothing
Bearer token or ?key=
The key also unlocks Pro in the app

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Or pay in USDC over x402, per month or per call Agentic payments for software that cannot hold a subscription. A month for the same price, or a single answer for a cent with no key at all: call the endpoint, take the 402, sign, call again. How it works

Save as file

Your API key. Send it as Authorization: Bearer or ?key=. It also unlocks the app.

Medium One payment, kept for goodPrice $3.99 once, for the first 100,000 accountsAccount not required for the free version

09 · For builders

The engine answers for a coordinate

Ask for a coordinate or a slippy tile and get back the avalanche reading for that forecast zone, the active alerts with their full text, the land and boundary beneath it, and the nearest reporting instrument. A tile request is answered for the tile centre and cached by tile. The app calls the same functions.

# any point…
curl "https://snowpack.fyi/api/atlas?lat=40.581&lon=-111.655" \
     -H "Authorization: Bearer sp1...your-key"

# …or any slippy tile, cached for everyone who asks after you
curl "https://snowpack.fyi/api/atlas?tile=12/845/1550&key=sp1...your-key"

Software can pay for itself

An agent has no card and cannot hold a subscription. x402 is HTTP's own 402 Payment Required, used the way it was always meant to be: ask, get told the price, sign one USDC transfer, ask again. No account, no key, no sign-up. Pay a cent for one answer, or 5.99 for a month, and the month gives you a key that also unlocks the app.

# ask, and be told the price
curl -i "https://snowpack.fyi/api/atlas?lat=40.581&lon=-111.655&pay=x402"
HTTP/1.1 402 Payment Required

# sign the authorization, ask again, get the answer
curl "https://snowpack.fyi/api/atlas?lat=40.581&lon=-111.655"      -H "X-PAYMENT: $(your_wallet_signs_it)"

# or buy a month, and get a key
curl -X POST "https://snowpack.fyi/api/x402" -d '{"buy":"api"}'      -H "X-PAYMENT: $(your_wallet_signs_it)"

# everything on offer, in one answer no wallet is needed to read
curl "https://snowpack.fyi/.well-known/x402"

Medium HTTP 402, paid per requestStandard x402, versions 1 and 2, exact schemeAsset USDC on BaseSettlement on chain, before the answer is sent

Medium JSON over HTTPS, by coordinate or slippy tileCache answered for the tile centre, cached by tileCaller the same functions the app calls

10 · The ground

Every number says where it came from

Every figure carries one of three labels on screen, next to the number: measured, reported or modelled.

Measured

An instrument on or near the mountain reported the value. Snow telemetry is read from the government sensor network and passed through three filters: a noise floor below the sensor's own resolution, spike rejection, and a bare-ground check. The station, its elevation and the reading time are shown.

Reported

A forecast office or avalanche centre published the value for this ground. It is shown with its full text, its issuing office or zone, and its valid period.

Modelled

The value was computed for this coordinate from a numerical weather model. The model and its run time are shown. The label appears next to the figure and is spoken in the audio brief.

The elevation source is named The app names the elevation source that built the mountain in front of you and its nominal resolution, and reports the result of the summit-elevation check run against the survey after the terrain is built.
When a stage of the load fails A mountain whose terrain could not be loaded shows a title card naming which stage failed: the elevation route, the feature route, or the tile decode, with what to try next.
Feet, inches and miles Elevations, depths, distances and speeds are stored in one unit internally and converted once at display: feet, inches, miles and miles per hour.

Medium Provenance carried beside every figureClasses measured, reported, modelledFilters noise floor, spike rejection, bare-ground check

11 · What is next

Sixty-three today, and the work is written down

A mountain is added by baking its survey, clipping it to its permit boundary and verifying it against the current standard. What is in build, in order.

NowTrees and structures to the standard of somewhere you can walk into. Ski patrol buildings researched to scale. Ski patrol buildings researched to scale. The last non-standard lifts.
NextNamed peaks in feet on the horizon, bare bowls and rock as their own surfaces, roads that carry their own names and distances.
AfterEvery base village in its own architecture, researched from several independent sources.
TestingEvery fixed defect gets a permanent automated check. There are about ninety, covering geometry, lift machinery, physics, night legibility, the danger scale, patrol verification and page copy, and all of them run before anything ships.

Medium The build list, in the order it is workedMethod bake the survey, clip to the permit, verify to standard

Open it on the mountain you are going to

The free version needs no account and no payment details. Avalanche danger, weather warnings, ski patrol and SOS are in it.

Free version Pro, $3.99