Some high-elevation snow will spread across the Sierra Nevada and into Colorado’s San Juan Mountains above 9,000 feet before 00Z Sunday, Nov. 1, the Weather Prediction Center says. That deadline falls at 5 p.m. PDT and 6 p.m. MDT on Saturday, Oct. 31, so the snow is due as Halloween evening begins. The line comes from a discussion issued at 1752Z on Oct. 28, 2026, and at 9,000 feet it sits above Donner Summit, Echo Summit and Carson Pass, the Sierra crossings that stay open all winter.
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Which Sierra crossings reach the 9,000-foot line
The clock matters as much as the elevation. The discussion’s Day 3 begins at 00Z Saturday, 5 p.m. PDT on Friday, Oct. 30, and runs 24 hours to that Sunday deadline. Zulu time 00Z Sunday converts to the early evening of Halloween itself, because daylight saving time does not end until 2 a.m. on Sunday, and the forecast describes snow arriving by then rather than falling through the night.
The elevations decide who feels it. Wikipedia’s list of Sierra Nevada road passes gives Tioga Pass at 9,943 feet and Sonora Pass at 9,624, both above 9,000 and both closed in winter, along with Ebbetts Pass at 8,732 and Monitor Pass at 8,321. The year-round crossings sit lower: Carson Pass at 8,573, Echo Summit at 7,377 and Donner Pass at 7,088. The gap between the 9,000-foot line and Donner Pass is 1,912 feet, and 1,623 feet to Echo Summit. A 9,000-foot snow line therefore touches only the seasonally closed high routes, which carry little traffic once the winter gates close.
The lower crossings have their own forecast. NWS Reno’s discussion issued at 1:43 a.m. PDT on Tuesday, Oct. 27, signed “-Justin,” expected snow levels “around 5000-6000 feet, potentially lower at times, especially Saturday night,” with precipitation chances of 40% to 50% across the Sierra and its foothills on Saturday and Sunday. Snow at 5,000 to 6,000 feet would reach below Donner and Echo, which is the difference between the national center’s high-elevation line and what the Reno office describes for the same weekend.
Reno called the weekend the main unsettled period of the forecast, with widespread rain and snow across its area on Saturday, Oct. 31 and Sunday, Nov. 1. The mixed rain-and-snow description matters for the 9,000-foot line: below it, the same system may fall as rain, and the dividing elevation is what the later forecasts will move up and down.
Minimal Day 3 snow, wetter weather behind it
The national text is cautious about amounts. Day 3 snowfall is expected to be minimal, and most precipitation from the system falls after Day 3, mainly from Day 4 onward, the Weather Prediction Center’s discussion says. Forecaster Weiss added that very moist air gives a low snow-to-liquid ratio, with a 10-30% chance of at least minor impacts from snow load developing before the risk expands in Day 4.
Low ratios mean each inch of snow carries more water weight, which is the mechanism behind a snow-load concern for trees and lines.
The Reno office was frank about uncertainty. Its discussion said timing and amounts are still being refined, with large model spread and a wide range of 24-hour precipitation totals for the Sierra from Tahoe southward through Sunday afternoon. Earlier chances of 10% to 30% begin as soon as Thursday night, with snow levels near 6,000 to 7,000 feet, continuing into Friday. A traveler reading only the 9,000-foot figure would miss that the lower levels, and the larger totals, are forecast for later in the weekend.
San Juan highways and the Sunday moisture peak
On the Colorado side, NWS Grand Junction’s discussion issued at 5:21 p.m. MDT on Oct. 27, signed with the initials “BW,” does not name the San Juans or Halloween. It refers to southwestern Colorado and says isolated storms may start Friday with minimal precipitation. “By Sunday though, moisture will be hitting its peak,” the forecasters wrote of their forecast area, with the most significant impacts Sunday into Monday morning.
The office also said precipitable water could reach up to 300% of normal if the moisture plume passes south of the area. A cold push is expected to drop temperatures to around 10 degrees below normal, and the office said that “could be enough to drop snow level 1-2 kft.” Forecasters expressed low confidence in where and when snow will fall. They also flagged flooding as a concern if precipitation is significant, since areas are still recovering from last week’s rain.
The mountain highways involved are the ones the Colorado Department of Transportation’s maintenance crews cover each winter. A CDOT notice on reopening the southwest passes lists Red Mountain, Molas and Coal Bank passes on U.S. 550 and Wolf Creek Pass on U.S. 160 among them, without elevations.
The open question for the holiday weekend is timing. The national center puts the 9,000-foot snow before 00Z Sunday and the bulk of the precipitation after it, while Grand Junction places the moisture peak on Sunday. If those schedules hold, Halloween evening brings the first flakes to the high country, and the heavier test for both ranges comes in the days that follow.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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