Avalanche Danger Overlay
Avalanche Danger colors each avalanche forecast zone by its current danger rating. The ratings come from the avalanche center that forecasts for that area, and Slopes shows them without changing them.
The danger scale
North American forecasters use the North American Public Avalanche Danger Scale. Each level reflects how likely avalanches are, how large they'll be, and how widespread (avalanche.org).
| Level | Travel advice |
|---|---|
| 1, Low (green) | Generally safe conditions. Watch for unstable snow on isolated terrain features. |
| 2, Moderate (yellow) | Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully. |
| 3, Considerable (orange) | Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. |
| 4, High (red) | Very dangerous avalanche conditions. Travel in avalanche terrain is not recommended. |
| 5, Extreme (black) | Avoid all avalanche terrain. |
The steps between levels get bigger as you go up the scale, so a trip into avalanche terrain on a High day is much riskier than the same trip on a Considerable day. Even so, more people have historically died on Considerable days than at any other level (avalanche.org). Far more people head out on Considerable days, and the danger is easy to underestimate. Human-triggered avalanches are likely, but there often aren't obvious warning signs like fresh natural slides.
What the color shows
Each zone gets one color: the highest rating anywhere in it. Most forecasts rate danger separately by elevation, and some European forecasts give separate morning and afternoon ratings. The map always shows the highest of these, so the slope you're planning may have a lower rating than the zone's color. Open the center's forecast to see the rating for each elevation and time of day.
A single rating also covers a large area, sometimes hundreds of square miles, and individual slopes can be safer or more dangerous than it suggests. In Colorado, forecast areas follow the Colorado Avalanche Information Center's own terrain patches, which change from day to day.
Opening a zone
Tap a zone to open the avalanche center's full forecast. It's the center's own page, so it has the details the map can't show, like which aspects and elevations each problem affects and the center's travel advice.
Places, areas and routes also show an avalanche card with the danger level, up to two of the day's avalanche problems, the zone name, the forecaster and when the forecast was issued.
Gray zones
A gray zone labeled No Rating has no current rating to show. The center may not be rating danger that day (common early and late in the season), the last forecast may have expired, or the forecast may still be loading. Areas outside any forecast zone aren't colored at all. Avalanches can happen in either case.
Before you head out
The map shows each zone's rating, but not when the forecast was issued or when it expires. Tap the zone and read the center's full forecast every time, so you know you're looking at today's. The overlay also needs a data connection, so check it before you lose signal.