The Climate Prediction Center issued its hazards outlook at 3:00 p.m. EST on Nov. 10, covering Wednesday, Nov. 18, through Tuesday, Nov. 24, and it lists a slight risk of heavy snow for the Colorado Front Range, southeastern Wyoming and the Central to Southern Rockies. The discussion text carries no moderate-risk statement for the Rockies. A map described in an Autoblog report published the same day had singled out the San Juan Mountains as the only moderate-risk area, so the signal shifted between versions.
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Forecasters tied the setup to a closed low over the Four Corners and a deepening surface low over southeastern Colorado, a pairing the outlook says would bring a winter storm risk to the Denver area. Wind adds a second hazard. The same product posts a slight risk of high winds from the West Coast east to the Great Plains through Nov. 24, so mountain passes could see blowing snow even where totals stay modest.
The Nov. 18-24 slight-risk zones
NOAA’s Climate Prediction Center hazards outlook lists higher elevations of the Klamath, Sierra Nevada and Wasatch mountains alongside the Central to Southern Rockies under its slight heavy-snow category. The detailed summary adds the Colorado Front Range and southeastern Wyoming by name. The product is a week-two outlook, which means it describes where the odds of a significant event are elevated rather than forecasting a specific snowfall total for any town or pass.
Slight risk carries no snow probability in the text. The only percentages in the discussion belong to other hazards: a better than 20 percent chance of more than one inch of rain for the Mississippi Valley, and a below 20 percent chance of exceeding the 85th percentile of three-day precipitation north of southwestern Oregon. For the Rockies, the category itself is the message.
San Juan Mountains and the earlier moderate-risk map
Adam Lynton, co-editor-in-chief of Autoblog, wrote on Nov. 10 that a NOAA map credited to the Climate Prediction Center showed the San Juan Mountains of Colorado at moderate risk on Tuesday, Nov. 17, with better than a 40 percent chance of more than 6 inches of snow. The report named the San Juans as the only moderate-risk area in a window running Nov. 17 through Nov. 23, with the Wasatch Range, the Sierra Nevada and the Klamath Mountains rated lower.
The outlook read for this article, stamped 3:00 p.m. EST on Nov. 10, starts one day later and does not name the San Juans. Autoblog noted that the Climate Prediction Center refreshes the product every weekday, which explains how two versions published within hours of each other can disagree on the region and the date. Anyone planning around Nov. 17 specifically should treat that day as outside the current window.
Local forecasters were not committing either. The National Weather Service office in Grand Junction, in a discussion issued at 10:10 p.m. MST on Nov. 9, said models show a deep trough developing off the West Coast by the end of the week, which could bring cooler, wetter conditions to eastern Utah and western Colorado over the weekend. Its blunt caveat was that “Model agreement remains poor this far out.”
The Boulder office was equally restrained. Its forecast discussion from 4:26 a.m. MST on Nov. 10 found no specific storm risk for the following week, expected temperatures to cool toward the start of the week with seasonal readings returning, and allowed only for “possibly a more active pattern.” It put a 30 to 40 percent chance of light mountain rain or snow on a weak weekend system and signed off with “Stay tuned…”
Practical planning still starts with the dates. Because the outlook is a week-two product, it flags where heavy snow is more likely than normal rather than predicting a storm on a specific day, and a slight risk can verify with modest totals in one valley and a foot on a pass in the next. Travelers with plans in the Colorado high country for the Nov. 18-24 stretch have a full week of updates ahead.
Colorado traction law and the 3/16-inch tread minimum
If a storm does reach the mountains, the Colorado Department of Transportation’s traction law sets the bar for drivers. Passenger vehicles need at least 3/16 inch of tread on tires rated all-weather or winter, or must carry chains or an approved alternative traction device. On the Interstate 70 corridor from Morrison to Dotsero the law covers Sept. 1 through May 31 or whenever conditions require, and CDOT can apply it on any state highway.
Penalties start at a $100 fine plus a $33 surcharge. If a noncompliant vehicle causes a travel lane to close in one or more directions, the fine rises to $500 plus a $157 surcharge. Autoblog’s report listed U.S. 550 over Red Mountain Pass and U.S. 160 over Wolf Creek Pass, both in the San Juan country, among the routes where the rule is typically activated.
The open question is whether the San Juans reappear in the Climate Prediction Center’s next issues. The Nov. 10 text puts the Front Range storm risk on a closed low whose track the Grand Junction forecasters called poorly agreed upon, so the area, window and category could all change before Nov. 18 arrives.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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