How to Use This Calculator
- 1
Input Slope Angle
Enter the steepest angle of the slope in degrees. Angles between 30° and 45° carry the highest risk.
- 2
Enter Recent Snowfall
Provide the inches of new snow in the past 24–48 hours. Significant new snow increases instability.
- 3
Specify Wind Speed
Input the sustained wind speed at ridge level in mph. Winds above 15 mph transport snow, creating slabs.
- 4
Provide Total Snowpack Depth
Enter the accumulated snowpack depth in inches. Deeper snowpacks can store more energy for slides.
- 5
Configure Advanced Parameters (Aspect & Rain)
Optionally expand Advanced Parameters to set slope direction (e.g., North, East) and indicate recent rain-on-snow conditions.
- 6
Review Avalanche Risk Level & Breakdown
Check the primary Risk Level card, Risk Score (/10), Snow Load, Wind Slab Risk, Aspect Hazard, Estimated Runout Zone, and detailed Factor Breakdown.
Example Calculation
A backcountry skier is planning a route on a north-facing slope after recent snowfall and moderate wind.
Slope Angle (°)
35
Recent Snowfall (in)
10
Wind Speed (mph)
15
Total Snowpack Depth (in)
48
Slope Aspect
North (N)
Recent Rain on Snow
No
Results
Avalanche Risk Level
Considerable
Risk Score
5.5/10
Est. Snow Load
50 lb/ft²
Est. Runout Zone
168 ft
Tips
Always Consult Official Forecasts
This calculator provides an initial risk estimate. Always cross-reference with your regional avalanche forecast center (such as Avalanche.org in North America) before traveling in the backcountry.
Recognize Red Flags in the Field
Watch for physical indicators of instability: recent avalanches, shooting cracks, 'whumpfing' collapsing sounds, rapid warming, or heavy drifting snow.
Use Advanced Options & Review Factor Breakdown
Expand the Advanced Parameters to factor in slope aspect and rain events, then inspect the Risk Factor Contribution bar to see which variable drives the majority of hazard.
Assessing Mountain Hazards: The Avalanche Risk Calculator
For anyone venturing into snow-covered terrain, evaluating avalanche risk is critical for survival and decision-making.
This Avalanche Risk Calculator analyzes key environmental parameters—slope angle, recent snowfall, wind speed, snowpack depth, slope aspect, and rain-on-snow events—to compute an overall avalanche risk score on a 0–10 scale.
For example, a north-facing slope inclined at 35° with 10 inches of fresh snow, 15 mph wind loading, and a 48-inch total snowpack yields a Considerable hazard rating (5.5/10), signaling heightened instability where human-triggered slides are likely in 2026.
Understanding Avalanche Risk Factors
Avalanches occur when gravitational stress exceeds the strength of a weak layer in the snowpack.
The calculator weights six core environmental factors:
- Slope Angle: Prime slab terrain ranges from 30° to 45° (3.0 risk points).
- Recent Snowfall: 10 inches of fresh snow adds roughly 50 lb/ft² of new load (1.0 risk point).
- Wind Loading: Sustained 15 mph winds actively transport surface snow onto leeward slopes (0.5 risk points).
- Total Snowpack Depth: A 48-inch snowpack stores significant potential energy for failure (0.5 risk points).
- Slope Aspect: North (N), Northeast (NE), and Northwest (NW) aspects remain cold and shaded, preserving persistent weak layers (0.5 risk points).
- Recent Rain: Liquid precipitation rapidly degrades bond strength between snow grains (1.5 risk points when present).
Step-by-Step Worked Calculation
Let's walk through the exact calculations for the default backcountry scenario:
- Slope Angle: 35° → 3.0 points (Prime avalanche pitch)
- Recent Snowfall: 10 inches → 1.0 point (6–12 in range)
- Wind Speed: 15 mph → 0.5 points (15–25 mph wind transport)
- Snowpack Depth: 48 inches → 0.5 points (40–80 in depth)
- Slope Aspect: North (N) → 0.5 points (Shaded cold aspect)
- Recent Rain: No → 0.0 points
Total Hazard Score: 3.0 + 1.0 + 0.5 + 0.5 + 0.5 = 5.5 / 10 (55% hazard index) Risk Classification:ConsiderableEstimated Snow Load: 10 in × 5 lb/ft² = 50 lb/ft²Estimated Runout Zone: 48 in × 3.5 = 168 ft
The North American Avalanche Danger Scale
The calculated hazard maps directly to standard North American Avalanche Danger ratings:
- Low (0.0 – 2.9): Generally safe conditions; watch for isolated instabilities on extreme terrain.
- Moderate (3.0 – 4.9): Heightened avalanche danger on specific aspects and elevations. Evaluate snow and terrain carefully.
- Considerable (5.0 – 6.9): Dangerous avalanche conditions. Human-triggered avalanches are likely. Conservative route selection is mandatory.
- High (7.0 – 8.9): Very dangerous conditions. Natural and human-triggered avalanches are very likely. Travel in avalanche terrain is not recommended.
- Extreme (9.0 – 10.0): Extraordinary hazard. Widespread natural avalanches expected. Avoid all avalanche terrain.
Frequently Asked Questions
What is an avalanche risk calculator?
An avalanche risk calculator estimates the potential hazard for a snow slide by evaluating key variables including slope angle, recent snowfall, ridge-level wind speed, snowpack depth, aspect, and temperature/rain conditions. It outputs a score from 0 to 10 along with official hazard categories (Low, Moderate, Considerable, High, Extreme).
What slope angle is most prone to avalanches?
Slopes with angles between 30° and 45° are most prone to avalanches, with peak frequency occurring around 38°. Slopes below 25° rarely slide, while slopes above 55° slough snow continuously, preventing large slab accumulation.
How does new snowfall increase avalanche risk?
New snowfall adds mass and shear stress onto existing weak snow layers. Accumulations of 6 to 12 inches introduce moderate instability, while 18 inches or more of fresh snow creates severe slab avalanche conditions.
Why is wind speed important for avalanche forecasting?
Sustained winds above 15 mph transport loose surface snow across ridges, loading leeward slopes up to 10 times faster than direct snowfall alone and creating dense, fragile wind slabs.
How is the runout zone estimated?
The runout zone projects the potential reach of a slide down-slope. For prime terrain (30°–45°), the runout distance is estimated at approximately 3.5 times total snowpack depth.