How X4D works
Everything on X4D is generated automatically from public data. This page explains where it comes from, how ratings are calculated and what the limitations are, so you can judge how much to rely on it.
Data sources
- Forecasts come from the National Weather Service gridded forecast for the point at the center of each area: temperature, wind and gusts, chance and amount of rain and snow, sky cover, visibility and weather types such as thunderstorms, smoke and blowing dust.
- Weather alerts are the active NWS watches, warnings and advisories for each area, checked roughly every 40 minutes.
- Space weather comes from the NOAA Space Weather Prediction Center: the planetary K index, used for aurora and drone GPS warnings.
- Satellite orbits for the International Space Station come from CelesTrak. Pass predictions and sun and moon times are calculated in your browser.
Each area's forecast refreshes roughly every two hours on a rotating schedule.
Ride rating
For each hour, X4D starts at 100 points and subtracts for conditions that make riding worse or riskier: thunderstorms, rain, strong gusts (with a lower threshold for sand and desert, where wind means blowing sand and dust), heat above 98°F, cold below 28°F, snow, freezing rain, smoke, dust, fog and poor visibility. Trail surface also counts: muddy or very muddy dirt trails lower the rating. Scores map to ratings: Great (80 and up), Good (60 to 79), Fair (40 to 59), Poor (20 to 39) and No-go (below 20). Daily ratings use the better half of daytime hours from 7 am to 7 pm, since most riders can choose when to go. Any active warning for flash floods, severe thunderstorms, tornadoes, high or extreme wind, dust storms, extreme heat, red flag fire conditions or winter storms sets the current rating to No-go.
Trail surface
The weather service does not publish how much rain actually fell at every riding area, so X4D estimates it. Each time an area refreshes, X4D records the rain amounts for the hours that have just passed, as given by the most recent forecast. Over time this builds a running log of recent rainfall for every area. The surface estimate weights the last 24 hours most heavily, then the 24 to 48 and 48 to 72 hour periods, plus rain expected in the next 12 hours. How that rain affects the trail depends on terrain: dirt turns to mud, rock gets slick, sand packs down and desert washes may run. For spot checks of locations not on the list, only the rain hours included in the current forecast are available, so the estimate is less complete.
Drone conditions
Each hour is rated no-fly, caution or good from wind, gusts, rain, visibility, temperature and the K index, using the thresholds in the drone guide. They cover weather only, not airspace or land rules.
Limitations
- Forecasts are for one point at the approximate center of each area. Large areas, mountains and canyons can have very different weather from one end to the other.
- Rainfall is estimated from forecasts, not measured by gauges. Local storms can be heavier or lighter than estimated.
- X4D does not know about trail closures, permits, fire restrictions or events. Always check with the land manager.
- If the weather service is unavailable, pages keep showing the last good data along with the time it was updated.