Avalanche Risk in the US: How FEMA Scores It and How to Prepare

Avalanches are the National Risk Index’s most specialized hazard: they threaten a narrow slice of mountain America, and unlike nearly every other hazard on this site, the victims mostly choose their exposure. Around 25–30 people die in US avalanches in a typical winter — almost all of them backcountry skiers, snowboarders, snowmobilers, and climbers who triggered the slide themselves. In the NRI, avalanches (hazard code AVLN) account for roughly $420 million in national expected annual loss across 684 mountain counties.

What counts as avalanche risk

An avalanche is a mass of snow releasing and accelerating down a slope — the dangerous kind is the slab avalanche, where a cohesive plate of wind- or storm-deposited snow fractures on a buried weak layer and takes the slope with it, reaching 60–80 mph within seconds. The recipe: a slope steep enough to slide (roughly 30–45 degrees — prime skiing terrain, not coincidentally), a weak layer in the snowpack, and a trigger. In 90% of fatal accidents, the trigger is the victim or someone in their party.

Risk to fixed infrastructure — homes, highways like Little Cottonwood Canyon or US-550, ski areas — exists but is heavily managed with explosives, closures, and snow sheds. The unmanaged risk is the backcountry, and it has grown as lightweight gear and snowmobile power put far more people on avalanche terrain.

How the NRI measures it

FEMA combines each county’s exposure (population and property in avalanche terrain), annualized avalanche frequency, and historic loss ratios — dominated by the valuation of fatalities — into an Expected Annual Loss scored 0–100 against all counties. Because deaths drive the dollars, the ranking tracks where recreation meets serious snowpack, not just where the most snow falls.

Where the risk concentrates

Teton County, WY (Jackson Hole) leads the nation — score 100, ~$23M expected annual loss, and roughly two significant avalanche events a year in the data. Alaska takes three of the top five slots: Matanuska-Susitna Borough (the Talkeetna and Chugach ranges’ snowmobile country), Kenai Peninsula Borough, and the Copper River area, with Park County, MT (the Absarokas, north of Yellowstone) rounding out the group. Colorado — which leads the nation in avalanche deaths most winters — blankets the high-rating list with its San Juan, Elk, and Front Range counties, alongside Utah’s Wasatch and Washington’s Cascades.

How to read your county’s score

If your county scores high, avalanche risk is a real feature of local winters — but it is overwhelmingly avoidable risk. For residents: know whether your home, access road, or commute crosses mapped runout zones (mountain counties publish these), and respect highway closures — they exist because control work is imminent. For anyone who travels the winter backcountry, the county score is beside the point: your risk is determined by terrain choice, snowpack, and training, every single day.

What actually reduces the risk

• Check the forecast — every time. Regional avalanche centers (avalanche.org) publish daily danger ratings by elevation and aspect. Most fatal accidents happen on days the danger was rated Considerable or higher — the ratings work if you obey them.
• Get trained. An avalanche course (AIARE Level 1 or equivalent) teaches the terrain recognition and decision frameworks that actually prevent burials. Slope angle is learnable: under 30 degrees, slab avalanches essentially don’t start.
• Carry the trio, know the trio: transceiver, probe, shovel — on your body, practiced regularly. A buried victim’s survival drops below 50% after 15 minutes; rescue comes from your own party or not at all. Airbag packs add meaningful survival margin.
• Travel protocol: one at a time on suspect slopes, watch your partner from safe ground, never assume tracks mean stability — a slope can hold a dozen crossings and fail on the thirteenth.
• Snowmobilers are now half of US fatalities: high-marking on steep faces is the signature fatal maneuver, and machine burials are deep. Same forecast, same gear, same training apply.
• In-bounds at ski areas is a different world — avalanche risk inside open, controlled runs is very low. The rope line is the risk boundary; ducking it puts you in uncontrolled snowpack, legally and physically alone.

Sources

• Avalanche.org — daily forecasts from all US avalanche centers
• FEMA NRI avalanche methodology
• Colorado Avalanche Information Center accident reports
• AIARE avalanche education