Rain turned to wet snow across north-central Montana on the evening of Oct. 23, and the National Weather Service had Winter Weather Advisories posted for mountain and foothill zones from the Bears Paw Mountains to the Gallatin, Madison and Bridger ranges. The change came behind a strong cold front that the Weather Prediction Center expected to move down the terrain into the northern Rockies late Friday, dropping temperatures sharply. Snowfall totals were forecast in inches, not feet.
Save more, waste less: The Cool Down’s newsletter sends smart, simple changes that help you and the planet in your everyday life.
We may earn a commission if you sign up.
Two layers of National Weather Service forecasting describe the same event. The national desk at the Weather Prediction Center laid out the setup two days ahead of the weekend, and the local forecast office in Great Falls supplied the hour-by-hour detail as the snow arrived. Together they show a classic first-snow pattern for the northern Rockies: a warm, wet system followed by cold air from Canada.
The Weather Prediction Center’s rain-to-snow call
The Weather Prediction Center’s short-range discussion issued at 4:08 p.m. EDT on Oct. 22, signed by forecasters Asherman and Kebede, said a lee-side cyclone was expected to develop over the Northern High Plains as an upper trough arrived from the North Pacific. By late Friday, the discussion said, a strong cold front would move down the terrain into the northern Rockies and temperatures there would drop sharply. In that area, the forecasters wrote, “a transition from rain to snow could lead to a few inches of snowfall.” The discussion also noted that Winter Weather Advisories were in effect, though it did not list the zones, and it stayed with “could” for the snowfall.
The same product was written for the period from Oct. 23 through Oct. 25 and also covered the Heartland cooling and flash flooding in the Four Corners, so its northern Rockies paragraph is brief.
What Great Falls forecast on Oct. 23
The local detail came from the National Weather Service office in Great Falls, Montana, in a discussion issued at 6:50 p.m. MDT on Oct. 23. Precipitation was transitioning to wet snow, reaching even the lowest elevations before ending that evening, and snow levels continued to lower. The office had issued an earlier discussion at 5:27 p.m. MDT the same day, and the 6:50 p.m. package is the later of the two. Snowfall rates in the band were above half an inch per hour, isolated totals in the foothills south and east of Lewistown approached 6 inches, and high-resolution models gave 80 percent or greater odds of at least 1 inch per hour across the Little Belt and central Montana island ranges between 4 and 7 p.m.
The advisories ran on different clocks. One covered the Bears Paw Mountains, southern Blaine and Fergus counties below 4,500 feet, the Judith Basin, Judith Gap and the Snowy and Judith Mountains until 3 a.m. MDT on Saturday, Oct. 24. Another covered Cascade County below 5,000 feet, the Southern High Plains and the southern Rocky Mountain Front until 9 p.m. on Oct. 23, and a third covered mountain zones including the Big Belt, Bridger, Castle, Gallatin, Madison and Centennial ranges until midnight. A separate High Wind Warning for Fergus County below 4,500 feet ran until 9 p.m. the same evening.
Behind the system, the discussion described an upper-level disturbance and its cold front moving east and a surge of colder air from Canada spreading across north-central and southwest Montana. It expected cooler than average and drier conditions from the weekend into early next week, with surface high pressure over the Canadian Prairies.
Winter Weather Advisory versus a warning
A Winter Weather Advisory is the lower tier of the National Weather Service’s winter products. According to the agency’s winter weather alert page, an advisory is issued when snow, blowing snow, ice, sleet or a mix is expected but should not be hazardous enough to meet warning criteria, and the guidance is to expect possible travel difficulties and drive with caution. A Winter Storm Warning, by contrast, covers a significant event where travel becomes difficult or impossible. The agency adds that each local office sets its own criteria, which is why an advisory in Montana can reflect different snow amounts than one elsewhere. The Great Falls text follows that logic: its advisories rest on rates above half an inch per hour and totals near 6 inches in a few foothill spots, not on a widespread heavy snowstorm, and the High Wind Warning for Fergus County is a separate product with its own criteria.
The driving risk is real even at advisory level. The National Weather Service’s winter safety page says thousands of people are injured or killed every year in traffic accidents related to slippery roads from winter storms. Its cold-weather page adds that cold air in early fall can damage or kill crops and home plants and flowers, and that frost can form on clear, calm nights when air temperatures are in the mid-30s, conditions that match the cooler, drier weekend with high pressure over the Canadian Prairies that Great Falls described. Drivers on mountain passes and foothill roads were the group most exposed on the evening of Oct. 23, when snow was falling at more than half an inch per hour in places and had reached the lowest elevations.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
Save more, waste less: Subscribe to The Cool Down →
We may earn a commission if you sign up.
More from Morning Overview
