5 more

HOTNational Avalanche Center, CAICFebruary 19, 2026🇺🇸 USSafety & Environment

🏔️

Tahoe Avalanche Warning: Backcountry Safety Alert

A series of avalanche incidents across the Sierra Nevada and Colorado Rockies has prompted heightened backcountry safety alerts. The National Avalanche Center reports above-average snowfall and persistent weak layers creating dangerous conditions. This calculator assesses avalanche danger using slope angle, aspect, snowpack stability, wind loading, and recent activity — based on the North American Avalanche Danger Scale and ATES terrain ratings. Always check local forecasts before backcountry travel.

Concept Fundamentals

1-5

Danger Scale

NAC standard

30-45°

Critical Slope

Most avalanche-prone

~90%

Survival at 15min

Drops to 30% at 30min

~25

US Deaths/Year

Backcountry average

Ready to run the numbers?

Why: Avalanches kill an average of 25 people per year in the United States, and most victims are experienced backcountry skiers and snowboarders who triggered the slide themselves. Understanding the interaction between terrain (slope angle, aspect, terrain traps), snowpack (recent snowfall, wind loading, weak layers), and human factors (group size, experience, equipment) is critical for making safe backcountry decisions. This calculator quantifies these factors into a danger rating aligned with the North American Avalanche Danger Scale.

How: The model evaluates seven weighted factors: slope angle (30-45° is the sweet spot for slab avalanches), aspect (north-facing holds persistent weak layers longer), recent snowfall (>30cm in 24h is a major loading event), wind speed and direction (creates wind slabs), temperature trend (rapid warming destabilizes), recent avalanche activity (strongest indicator), and terrain traps (gullies, cliff bands). Each factor is scored and weighted to produce a 1-5 danger rating. Trigger probability and survival curves are modeled separately.

Your terrain-specific avalanche danger rating (1-5 scale)Trigger probability based on snowpack and terrain interaction

Methodology

🏔️NAC Danger Scale

Produces a 1-5 danger rating aligned with the North American Avalanche Danger Scale used by all US and Canadian avalanche centers

⏱️Survival Probability

Models the well-documented burial survival curve: ~90% at 15 minutes, dropping to ~30% at 30 minutes and ~5% at 2 hours

📊Multi-Factor Analysis

Evaluates terrain, snowpack, weather, and human factors with weighted scoring — not a single-variable assessment

Sources:National Avalanche CenterCAIC

Run the calculator when you are ready.

Assess Your RiskUse the calculator below to see how this story affects you personally

⛷️

SAFETY ALERTFeb 19, 2026

Tahoe Avalanche — Backcountry Risk Assessment

Recent storm cycles have increased avalanche danger. Use this tool for educational risk assessment. Always check avalanche.org and local forecasts.

avalanche.org →Ski Slope Calculator →

Low

Level 1

Moderate

Level 2

Considerable

Level 3

High

Level 4

Extreme

Level 5

Sample Scenarios — Click to Load

Terrain

Slope Angle (°)

Aspect

Elevation (ft)

Snowpack

Snow 24h (in)

Snow 48h (in)

Snowpack Depth (in)

Weather

Wind Speed (mph)

Wind Direction

Temperature Trend

Group & Terrain

Avalanche Activity

Terrain Trap Below

Group Size

⚠️ CAUTION

Exercise extreme caution. Stick to lower-angle terrain, travel one at a time in exposed areas, and maintain visual contact.

⏱️ Burial Survival Window

92%

0-15 min

37%

15-35 min

20%

35-60 min

60+ min

Carry beacon, probe, and shovel. Practice companion rescue. Every second counts.

avalanche_risk.sh

ASSESSED

$ assess_risk --slope=35° --aspect=N --elevation=10000ft

Danger Level

3 — Considerable

Trigger Probability

51%

ATES Rating

Complex

Recommended Action

Caution

Safe Travel Recommendations

• Travel one at a time through avalanche terrain
• Carry beacon, shovel, probe — and know how to use them
• Check local avalanche forecast before departure

Risk Factor Radar

Risk Factor Breakdown

Survival Probability by Burial Time

Calculation Breakdown

TERRAIN

Slope Angle Score

0.95

35° → Critical zone (35-45°)

Aspect Score

0.90

N aspect (N/NE most dangerous)

Snow Load (24h/48h)

0.25

6" / 12"

Wind Loading

0.45

25 mph from NW

Temperature Trend

0.60

stable

Avalanche Activity

0.30

none

Terrain Trap

None

RESULT

DANGER RATING

3 — Considerable

Trigger Probability

51%

ext{Estimated} ext{human}- ext{trigger} ext{likelihood}

ATES

Complex

ext{Avalanche} ext{Terrain} ext{Exposure} ext{Scale}

RECOMMENDED ACTION

Caution

For educational and informational purposes only. Verify with a qualified professional.

Quick Answer

Avalanche risk assessment combines terrain (slope angle, aspect), snowpack conditions, weather (wind, temperature), and human factors. The NAC danger scale (1–5) guides travel decisions. Slopes 30–45° are the critical zone; survival drops sharply after 15 minutes of burial. Always check local forecasts before backcountry travel.

Key Takeaways

• 93% of avalanche fatalities occur on slopes between 30° and 45° — the critical angle zone
• Survival drops from ~90% at 15 minutes to ~30% at 30 minutes — companion rescue is essential
• The NAC danger scale (1–5) guides travel decisions: Considerable (3) and above require extra caution
• Terrain traps (gullies, depressions, tree wells) dramatically increase burial severity — avoid when possible
• Always check your local avalanche forecast (avalanche.org, CAIC, etc.) before any backcountry travel

Did You Know?

⚠️~150+ avalanche deaths occur worldwide each yearSource: avalanche.org

📅January through March are the most dangerous monthsSource: CAIC

📡Beacon-assisted rescue survival is ~90% within 15 minSource: Swiss Avalanche Institute

🏔️The 1910 Wellington avalanche (WA) killed 96Source: National Avalanche Center

🕳️Terrain traps can create 10+ foot burials in gulliesSource: Utah Avalanche Center

❄️Persistent slab problems can linger for weeks after a stormSource: CAIC

🔊"Whumpfing" — hollow collapsing sound — is a major red flagSource: avalanche.org

How Does Avalanche Risk Assessment Work?

Avalanche risk assessment combines terrain, snowpack, weather, and human factors. Strong slabs can sit on weak layers (depth hoar, surface hoar). When the weak layer fails, the slab releases.

Snowpack Layers & Weak Layers

Depth hoar and surface hoar create persistent weak layers. New snow or wind-loading adds stress. Warming or a skier can trigger failure.

Wind Loading & Solar Aspect

Wind transports snow to lee slopes (often N/NE). South-facing slopes can stabilize faster; north-facing hold dangerous slabs longer.

Terrain Traps

Gullies, depressions, tree wells concentrate avalanche debris. A small slide can cause deep burial.

Avalanche Types

• Slab: Most deadly — cohesive block releases on a weak layer
• Loose: Point-release, usually smaller
• Wet: Spring/sun — heavy, slow
• Glide: Entire snowpack slides on ground

Danger Scale (1–5)

• 1 Low: Generally safe
• 2 Moderate: Human-triggering possible on steep slopes
• 3 Considerable: Dangerous — careful route selection
• 4 High: Travel in avalanche terrain not recommended
• 5 Extreme: Avoid all avalanche terrain

Expert Tips

Companion Rescue

Practice beacon search, probe, shovel. 15 min is the critical window.

Route Selection

One at a time through avalanche terrain. Identify safe zones.

Timing

Avoid steep slopes during and 24–48 hours after storms.

Red Flags

Recent avalanches, whumpfing, shooting cracks. Reassess and consider turning back.

Comparison Table

Feature	This Calculator	Avalanche.org Forecast	In-Field Assessment
Danger rating estimate	✅	✅	✅
Terrain-specific inputs	✅	⚠️ Regional	✅
Real-time conditions	❌	✅	✅
Snowpack tests (ECT, etc.)	❌	❌	✅
Trigger probability	✅	⚠️ Implicit	✅
Survival/rescue info	✅	❌	❌
Educational tool	✅	✅	N/A

Frequently Asked Questions

What triggers avalanches?

Human triggers (skiers, snowboarders) cause most fatalities. Natural triggers include new snow, wind, warming.

How do avalanche beacons work?

Beacons transmit 457 kHz. In search mode they display distance/direction to a buried victim. Rescue within ~15 min is critical.

What is a persistent weak layer?

A layer of weak snow (depth hoar, surface hoar) that can persist for weeks. Slabs above can release when loaded.

What slope angle is safe?

Slopes under 25° rarely avalanche. The danger zone is 30–45°.

When is avalanche season?

Peak season is December through April in North America.

What do I do if caught?

Try to escape to the side. If caught, fight to stay on top. Create an air pocket. Yell when you hear rescuers.

How deep is dangerous burial?

Even 1–2 feet can be fatal. Terrain traps can create 10+ foot burials. Survival drops sharply after 15 minutes.

What is ATES?

Avalanche Terrain Exposure Scale. Simple = minimal exposure; Challenging = some paths; Complex = multiple paths, terrain traps.

Avalanche Safety by the Numbers

150+

Deaths/Year Worldwide

93%

On Slopes 30-45°

15 Min

Critical Burial Time

1-5

Danger Scale

Sources

avalanche.org ↗

National avalanche forecast & education

National Avalanche Center ↗

US avalanche information

CAIC ↗

Colorado forecasts

Swiss Avalanche Institute (SLF) ↗

Research & standards

⚠️ IMPORTANT DISCLAIMER: This calculator is for educational purposes only. ALWAYS check local avalanche forecasts before backcountry travel. No calculator can replace professional avalanche education (AIARE, Avalanche Canada), companion rescue training, and proper equipment (beacon, shovel, probe).