The Sierra Nevada storm originally reported by Autoblog on Friday has escalated significantly. What started as a Winter Storm Warning for Mono County and the Donner Pass area has expanded into warnings covering every major mountain corridor in California, from Lassen County south through Yosemite, Kings Canyon, and Sequoia National Parks. Snowfall totals have been revised sharply upward. Wind forecasts have increased. And the worst of it is arriving now.
What Has Changed
The original forecast called for up to 28 inches above 7,000 feet near Lake Tahoe and up to 4 feet at the highest peaks, with crest winds of 70 to 80 mph. Those numbers have moved.
NWS Sacramento issued a Winter Storm Warning at 10:34 AM Friday for the West Slope Northern Sierra and Western Plumas County, calling for 1 to 2 feet of snow above 4,500 feet and 3 to 4 feet at the highest peaks, with snowfall rates of 1 to 2 inches per hour from Saturday afternoon through Sunday. That Warning runs through 11 PM Sunday.
NWS Reno upgraded the Lake Tahoe Basin to a full Winter Storm Warning, with 6 to 10 inches at lake level, 12 to 28 inches above 7,000 feet, and crest gusts now forecast at 90 mph Saturday afternoon with 20 to 35 mph sustained winds for communities around the lake.
Mono County remains under a Warning with 70 to 80 mph crest gusts and up to 24 inches along the Sierra crest. And NWS Hanford reissued a Winter Storm Warning at 7:34 PM Friday covering Yosemite, Kings Canyon, and Sequoia National Parks through Sunday night, with 10 to 30 inches of snow above 7,000 feet. NWS Hanford is describing conditions as potentially life-threatening.
The net effect: the original story's top-end forecast of 4 feet has been revised by NWS Sacramento above 6,000 feet to 5 feet, and the wind ceiling has jumped from 80 to 90 mph at the crest. The Warning footprint has expanded from two zones to the full 300-mile length of the Sierra.
Chain Controls Are Already Active
As of Saturday afternoon, Caltrans has chain screenings active on I-80 in both directions. Eastbound trucks are being screened at Applegate in Placer County. Westbound trucks are being screened at Overland Trail Road in Truckee and at Mogul, 5 miles west of Reno.
Drivers must have maximum chains in their possession to proceed, and permit loads are prohibited. A high wind advisory is also in effect on the San Francisco-Oakland Bay Bridge, where travel is not recommended for campers, trailers, or permit loads.
These are the early stages. Snow levels are still dropping. By Saturday evening, they will fall to 6,000 to 7,000 feet, and by late Saturday into Sunday morning, they will crash to 4,000 to 4,500 feet. When that happens, the chain controls will tighten, and closures become likely. In February, a similar system shut down a 60-mile stretch of I-80 from Colfax to the Nevada state line and stranded hundreds of drivers for hours. The same scenario is on the table tonight.
The Highways
I-80 over Donner Pass. Already under chain screenings. With 12 to 28 inches forecast at pass elevation, 90 mph crest winds, and snowfall rates of 1 to 2 inches per hour, a full closure Saturday night through Sunday is the most likely outcome. When I-80 closes over Donner Summit there is no practical detour across the Northern Sierra.
Highway 50 to South Lake Tahoe. Echo Summit sits at 7,382 feet, squarely in the heavy snow zone. Highway 50 has the same closure risk as I-80 and fewer plowing resources. When both routes close simultaneously, as they did in February, there is no realistic alternative across the central Sierra.
Highway 395 (Eastern Sierra). The Warning names 395 with gusts to 40 to 45 mph and 2 to 6 inches of snow. Higher terrain west of 395 faces 6 to 12 inches. Side roads to Mammoth Mountain and June Mountain will be treacherous at best.
Highway 88 through Carson Pass (8,574 feet) and Highway 89. Both exposed to heavy snow and high winds with limited plowing resources. These are typically the first routes to close and the last to reopen.
Yosemite corridors (CA-120, CA-140, CA-41). With 10 to 30 inches above 7,000 feet and NWS Hanford warning of visibility below a quarter mile, expect closures and severe restrictions across all Yosemite approach routes through Sunday evening.
The Worst Window
Saturday night through Sunday morning. This is when the stronger second system arrives, snow levels crash to 4,000 to 4,500 feet, crest winds peak at 90 mph, and snowfall rates hit their maximum. If you are on a mountain highway during this window, you are likely to be stopped, stranded, or turned around. The heaviest accumulation runs from late Saturday morning through midday Sunday.
Sunday afternoon onward the storm weakens, but do not assume roads reopen quickly. Clearing multiple feet of heavy, wet spring snow off a mountain highway takes hours even after the snow stops, and overnight refreezing Sunday into Monday morning will keep surfaces hazardous.
What To Do Right Now
If you are on the California side of the Sierra and need to get to Nevada, or vice versa, your window has likely closed. Chain controls are active, conditions are deteriorating, and by tonight the passes will be in full storm mode.
If you are already committed to a crossing, Caltrans will require chains on most vehicles above 4,000 to 5,000 feet, and AWD with snow tires may still need chains under R-2 and R-3 controls. Carry chains and know how to install them before you need to. Pack a blanket, flashlight, portable phone charger, water, food, a folding shovel, and cat litter or sand for traction. Fill your tank before entering the mountains. If you get stranded, stay with your vehicle, run the engine for heat in 15-minute intervals, crack a window for ventilation, and wait for road crews.
For a full breakdown on preparing your vehicle for winter conditions, Autoblog's winter car readiness checklist covers everything from tread depth to emergency kit essentials. Our guide to best practices for driving in snow, ice, and rain is worth reviewing before you attempt any Sierra crossing this weekend. And if this storm is a reminder that your vehicle is not set up for mountain driving, Autoblog's list of the best cars and SUVs for snow and winter driving can help you think about what matters when the roads turn ugly.
The safest decision is to wait. Monday midday offers the earliest realistic window for a Sierra crossing once crews have had time to clear and treat the passes. Check Caltrans QuickMap or call 511 before committing to any mountain travel.
Track Conditions
Check Caltrans for current highway conditions, live traffic cameras, and chain controls. NWS Sacramento and NWS Reno forecast pages have the latest zone-level details. For Nevada road conditions, visit 511 Nevada.
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