Mammoth Mountain could get 3 to 6 inches of snow as low as 9,000 feet in the season’s first big Sierra storm

Mammoth Mountain could pick up 3 to 6 inches of snow as low as 9,000 feet on Wednesday and Thursday, Oct. 21 and 22, 2026, according to the NOAA Weather Prediction Center forecast summarized on Oct. 20 by Unofficial Networks. The storm was being described as the first significant snow of the season for the Sierra and the Rockies, arriving on a calendar that normally belongs to rain gear and early ski-resort construction. Forecasters stressed that the numbers were regional estimates, not promises for any one lift.

Help yourself and the planet: The Cool Down makes it easy to help yourself while helping the planet, with smart, simple changes to save more and waste less in your everyday life.

Get The Cool Down →

We may earn a commission if you sign up.

The setup matters for anyone with a stake in the mountain, from skiers watching for the first turns of the season to drivers crossing the high passes. Early-season snow often falls on warm ground and melts quickly, so a storm that dumps several inches at one elevation can leave a bare slope a few hundred feet lower. Totals in the Sierra swing sharply with elevation, which is why the forecast language is built around specific altitudes rather than a single number for the range.

The Weather Prediction Center forecast for 9,000 to 10,000 feet

Unofficial Networks reported that the Weather Prediction Center expected the heaviest snowfall above 10,000 feet, with 3 to 6 inches possible as low as 9,000 feet on Wednesday and Thursday. Mammoth’s summit stands at 11,053 feet, well above the elevations where the heaviest accumulation was expected, while the base area sits far lower and was less likely to see lasting snow. The article described the figures as “regional high-elevation forecasts rather than guaranteed totals” for individual lifts or base areas.

The best window for accumulation at California ski areas was Wednesday afternoon through Thursday, the roundup said. It also noted that June Mountain could see higher-elevation snow, though no reliable resort totals existed yet, and that Lake Tahoe resorts including Palisades Tahoe, Kirkwood and Heavenly might see snow at high elevations but with the strongest signal farther south. The piece warned that unusually warm temperatures would play a major role in how much of the precipitation fell as snow.

Odds from the Weather Prediction Center and NWS Hanford

The probabilities behind the 3-to-6-inch forecast were more striking than the central estimate. The same roundup said the Weather Prediction Center gave the southern Sierra Nevada a 40% to 70% chance of more than 8 inches of snow above 10,000 feet by Thursday night, and a 10% to 30% chance of more than 12 inches. Odds that wide reflect real uncertainty about where the rain-snow line would settle, since a few degrees of temperature decide whether a given elevation sees slush or powder.

The National Weather Service in Hanford, California, which covers the southern Sierra, supplied its own numbers, again as summarized by Unofficial Networks: a 55% to 70% chance of at least 4 inches above 8,000 feet, and a 50% to 65% chance of at least 6 inches above 10,000 feet. Readers who want the current local snow probabilities can check the NWS Hanford office page, which links a probabilistic snow forecast, since those figures update as the storm evolves.

First significant snow, tropical moisture and the rest of the storm

Weather.com’s Oct. 21 coverage framed the storm in the same terms, saying parts of the Sierra and Rockies could see the first significant snow of the season. Authors Jennifer Gray and Miriam Guthrie wrote that widespread totals should stay under 6 inches, though isolated peaks could reach a foot, and that rain could change quickly to snow at higher elevations. Their numbers are looser than the Weather Prediction Center’s probabilities, but they point in the same direction.

The snow was one end of a storm whose other end was rain and flooding. AccuWeather meteorologist Brandon Buckingham wrote that tropical moisture from the eastern Pacific would stream north ahead of a non-tropical storm approaching the West Coast, with rain and some mountain snow beginning in California on Tuesday night, Oct. 20, and the core of the storm arriving on Wednesday. That warm, wet origin is part of why snow levels were expected to stay high at first.

FOX Weather’s Oct. 21 report said more storms could develop on Thursday as the system moved east toward the Rockies, which means the Sierra’s snow window was a short one. By Thursday night the forecast odds were meant to resolve into actual totals, and the first measurements from the high Sierra would show which side of the wide probability ranges the storm landed on.

Elsewhere in the West, the same Oct. 20 roundup showed how the rain-snow line shifted by region. The National Weather Service in Salt Lake City expected about 3 to 6 inches above 9,000 feet in Utah on Friday, Oct. 23, with locally higher amounts, while forecasters in Great Falls, Montana, saw accumulating snow possible above roughly 4,000 feet starting that Friday. Mammoth’s window came earlier, on Wednesday and Thursday, which made it the first mountain in the group to find out whether the forecast would hold. The article called the biggest uncertainty how much precipitation would fall as snow at resort elevations.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

Help yourself and the planet: Get The Cool Down →

We may earn a commission if you sign up.