WASHINGTON, DC — A strong Halloween weekend storm is putting seven Western states under winter weather alerts and flood watches, with the National Weather Service warning that mountain roads could become dangerous and desert washes could flood. Colorado and Nevada are under winter storm warnings, while California, Utah, Idaho and parts of Colorado remain under winter weather advisories.
Flood watches are also in place across portions of Arizona, Nevada, Utah, New Mexico, Colorado and California. Forecasters say the system could produce as much as 18 inches of snow in the highest terrain and enough rain to trigger flash flooding in lower-elevation desert areas. More than 30 states are watching snow and storm threats this week.
Colorado mountains face the hardest hit from the storm
Southwest Colorado is expected to get the heaviest snowfall. The National Weather Service office in Grand Junction upgraded its watch Saturday morning to a winter storm warning for the Northwest and Southwest San Juan Mountains. Forecasters expect 12 to 18 inches above 10,000 feet, along with locally higher amounts and wind gusts as strong as 45 mph.
The warning begins at 6 a.m. Sunday and lasts until noon Monday. The weather service said travel could be very difficult to impossible, and the storm will still be active during the Monday morning commute. NWS Pueblo also issued a warning for the Eastern San Juans above 10,000 feet, where 8 to 14 inches are expected from Sunday evening into Monday morning.
Flood risk spreads across valleys and lower elevations in Colorado
The storm is not just a mountain snow event in Colorado. In the lower elevations, Pueblo forecasters say flooding is expected in parts of the Upper Rio Grande Valley and possible in the San Luis Valley. That means rain could create trouble even where snowfall stays limited or never reaches the ground.
Farther north, the Gore and Elk Mountains are under a winter weather advisory for 5 to 10 inches. The mix of heavy snow at high elevations and rain below the snow line creates a complicated travel picture, especially for drivers crossing mountain passes or heading into valley communities before and during the storm’s peak.
Nevada, the Sierra and the Wasatch are all in the storm's path
In Nevada, the National Weather Service in Elko issued a winter storm warning for the Ruby Mountains and East Humboldt Range in the northeast part of the state. Forecasters say those ranges could receive 12 to 16 inches above 7,500 feet through Sunday night, an upgrade from the earlier watch issued Friday.
California’s Sierra Nevada remains under winter weather advisories, with different totals depending on elevation. Outside Yosemite Valley, forecasters call for 4 to 8 inches between 7,500 and 9,500 feet and up to 18 inches at the highest elevations. Around Lake Tahoe, the forecast is 2 to 5 inches above 7,000 feet and as much as a foot on the tallest peaks.
Utah’s Wasatch Mountains south of Interstate 80 and the western Uintas could pick up 8 to 12 inches above 8,000 feet. In Idaho, the Sun Valley area could see up to 7 inches above roughly 7,000 feet, adding to a broad belt of mountain impacts across the interior West.
Desert flood watches cover Arizona, Nevada, New Mexico and parts of Utah
The flood threat reaches well beyond the mountain snow zone. Watches extend into parts of the Phoenix and Tucson areas, Grand Canyon Country, Lake Mead, Lake Havasu, Zion National Park and northwest New Mexico. That puts a wide stretch of the desert Southwest under concern for fast-moving water and sudden rises in washes and drains.
NWS Flagstaff said flash flooding is possible in northern Arizona because the ground is already saturated. Most of the watches in Arizona and Nevada remain in effect into early Monday. In areas where soils are already soaked, even a short burst of rain can quickly turn roads and low-water crossings hazardous.
Weather service warns drivers to prepare for dangerous mountain travel
The National Weather Service is urging mountain drivers to slow down and be ready for delays. Officials say motorists should keep a flashlight, food and water in the car if they have to travel in the mountains during the storm. Those precautions matter most where snow, wind and poor visibility can quickly make travel unsafe.
The weather service also says never to drive through flooded roads. That warning is especially important in the desert where water depth can be hard to judge and road surfaces can be undermined by moving water. With snow falling in the high country and flooding possible lower down, road conditions could change quickly through the weekend and into Monday.
A broad late-October storm pattern is affecting much of the country
This weekend’s system is part of a busy weather pattern stretching across the country, with more than 30 states watching snow and storm threats this week. The western storm stands out because it combines heavy mountain snow, wind and flood risk in the same event, forcing forecasters to cover a wide range of hazards at once.
For Colorado, Nevada and the rest of the affected West, the timing is especially important because the strongest impacts overlap with weekend travel and the Monday morning commute. The National Weather Service forecasts suggest that people in the high terrain should expect wintry road conditions, while those in lower desert areas need to stay alert for flash flooding and rapidly changing conditions.