1981 – The United States experiences its last avalanche with a comparable death toll when 11 climbers die on Mount Rainier, establishing a benchmark for future avalanche fatalities [10][14][17].

Jan 2026 – A fatal avalanche in the Castle Peak area kills a snowmobiler, highlighting the region’s persistent instability and foreshadowing the February disaster [11].

Feb 17, 2026 (morning) – The Sierra Avalanche Center issues an avalanche watch at 6:49 a.m. for Greater Lake Tahoe and upgrades it to a high‑danger warning at 5 a.m., warning of large slides within 24‑48 hours [15][9][13].

Feb 17, 2026 (11:30 a.m.) – A D2.5 avalanche the size of a football field strikes a 15‑person backcountry ski party near Castle Peak as the group attempts to exit Frog Lake Huts, burying eight skiers and guides, leaving one missing and six survivors [10][13][15][17].

Feb 17, 2026 (afternoon) – Emergency beacons and an iPhone satellite SOS alert rescuers; roughly 50 responders, including snowcats and ski teams from Boreal Mountain and Alder Creek, reach the site within hours despite Highway 80 closures and gale‑force winds [3][4][9].

Feb 18, 2026 – Authorities recover eight bodies, confirm a ninth skier missing, and declare the incident the deadliest U.S. avalanche in 45 years, prompting a statewide “all‑hands” SAR effort, closures of I‑80 and 50, and a high‑avalanche‑danger alert that will remain in effect through Thursday [14][7][9][10].

Feb 18, 2026 – The U.S. Forest Service shuts the Castle Peak area to the public through Mar 15, citing unsafe terrain and weather, while the Nevada County Sheriff’s Office opens a criminal‑negligence inquiry into the guided tour [6][8].

Feb 19, 2026 – Governor Gavin Newsom calls the tragedy “horrible” on X and urges the public to stay out of backcountry terrain; Sheriff Shannan Moon and Capt. Russell Greene say investigators will examine why guides proceeded after the avalanche watch and warning [7][13][20].

Feb 19, 2026 – Washington father Jasper Boas cites the California disaster to stress avalanche safety for his children, and Northwest Avalanche Center forecaster Dallas Glass warns that a forthcoming heavy‑snow system could raise Cascades danger next week [19].

Feb 20, 2026 – Cal/OSHA launches a six‑month investigation into Blackbird Mountain Guides, while the Nevada County Sheriff’s Office confirms a criminal‑negligence probe; families publicly identify six mothers among the victims, including sisters Caroline Sekar and Liz Clabaugh, and express devastation [6][8][18].

Feb 20, 2026 – Rescue teams plan to resume recovery operations on Friday as the storm eases, though additional avalanches remain possible; the Sierra Avalanche Center keeps danger at level 4 and advises avoidance of avalanche terrain through the weekend [12][16].

Feb 21, 2026 – The death toll is officially updated to nine, confirming the avalanche as the deadliest U.S. event since 1981; the Nevada County Sheriff’s Office opens a formal investigation into possible criminal negligence, and authorities continue to search for the missing skier while bodies remain on the slope due to unsafe conditions [5][1][6].

Future (through Mar 15, 2026) – The Castle Peak region stays closed to the public, and ongoing investigations by the sheriff’s office, Cal/OSHA, and the Forest Service are expected to conclude by mid‑year, while avalanche forecasts remain elevated for the Sierra Nevada and the Cascades later in February [6][12][19].