A potent winter storm system is keeping much of the Western United States locked in a pattern of steady rain and mountain snow on Thursday, December 25, with impacts stretching from coastal cities to high mountain passes.

As holiday travelers continue to hit the roads and airports, forecasters warn of slower driving conditions, reduced visibility over key interstate corridors, and the potential for cascading delays across the air travel network.

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Storm System Brings Widespread Rain and High-Elevation Snow

A strong Pacific storm, enhanced by an atmospheric river type plume of moisture, is delivering rounds of rain to low-lying areas and heavy snow to higher elevations in states including Oregon, California, Nevada, and Arizona.

From the Willamette Valley around Portland to the Central Valley around Sacramento, radar and surface observations show periods of showers and steadier rain today, making for wet commutes on major routes such as Interstate 5.

In the Sierra Nevada and other high ranges, that moisture is translating into accumulating snow. Forecasters note that snow levels, which started higher earlier in the week, have been fluctuating but are low enough to cover many passes with fresh snow and slush. Windy conditions over ridges are also lifting the risk of blowing snow and sudden drops in visibility near the summits.

Farther inland, places like Reno in western Nevada and Flagstaff in northern Arizona are seeing a mix of showers in town and snow in the surrounding high country, a typical pattern when Pacific storms cross the Great Basin and the Four Corners region. The result is a broad footprint of unsettled weather that touches almost every major overland route through the interior West.

California Travel Corridors Face Heavy Rain, Wind and Sierra Chain Controls

California is experiencing some of the most disruptive conditions as the storm continues to move onshore. In the Sacramento Valley, a high wind warning is in effect with gusts that can reach highway-sign-shaking speeds, making driving difficult for high-profile vehicles and raising the risk of downed branches and sporadic power outages. Combined with steady rain, these winds are producing pockets of ponding on roadways and the possibility of hydroplaning at freeway speeds.

To the east, in the Sierra Nevada, a winter storm warning remains in force from late December 23 through the morning of December 26. Multiple feet of new snow are expected at the highest elevations, with significant accumulations at pass level as temperatures cool.

Transportation officials have already required chains over parts of Interstate 80 and other key routes that link the San Francisco Bay Area and Sacramento to Reno and Lake Tahoe, a pattern that is likely to continue through today.

South of the Sierra, the storm’s moisture is also spreading into Southern California, where forecasters have highlighted a heightened risk of flash flooding in vulnerable areas.

Steep terrain, recently burned hillsides and canyon roads along and near Interstate 5, including the Grapevine, are under special scrutiny. Officials caution that short delays can quickly become extended closures when rockslides or mudflows cover traffic lanes, especially in narrow mountain sections that have few detour options.

Oregon and the Pacific Northwest: Wet Roads and Mountaintop Snow

In Oregon and the broader Pacific Northwest, the same storm track is maintaining an unsettled pattern characterized by frequent showers at lower elevations and continuing snow over the Cascades.

Around Portland, drivers on Interstate 5 and the Interstate 205 loop are navigating slick pavement and bursts of heavier rain that can briefly reduce visibility, especially when combined with spray from trucks and holiday traffic volumes.

Higher up, along passes such as Government Camp on U.S. 26 and Santiam Pass on U.S. 20, road crews are dealing with periodic snow and a wintry mix. Even when temperatures hover close to freezing, a thin layer of slush can turn the roadway treacherous, particularly during periods of heavier snowfall when plows struggle to keep up.

Oregon transportation officials typically respond by lowering speed limits, increasing chain enforcement for commercial vehicles and urging drivers to carry traction devices in passenger cars.

While this particular storm is not the coldest of the season, the combination of marginal temperatures, steady precipitation and heavy traffic can still cause fender benders and spinouts that have an outsized impact on travel times.

Motorists crossing the Cascades are advised to check for chain requirements before departure and to build in extra time for unexpected slowing behind snowplows and crash scenes.

Nevada and Arizona: Mountain Passes Under Winter Weather Threat

In Nevada, the storm’s eastern flank is pushing showers and colder air over the Sierra’s east slopes and into the Great Basin. Reno is seeing episodes of rain, but the higher terrain surrounding the city, including the Mount Rose Highway and other routes that climb toward Lake Tahoe, are shifting to snow and icy conditions.

Forecasters at regional National Weather Service offices emphasize that as snow levels drop to near valley floors at night, more roadways can quickly transition from wet to slick.

Interstate 80 through Nevada remains a primary concern for long-haul truckers and holiday travelers alike, particularly over its western segments where the highway crests the Sierra and then continues east across exposed high desert.

Periods of heavier snow, gusty winds and poor visibility near the crest can set off chain controls and temporary closures that ripple eastward in the form of backups, missed delivery windows and tight flight connections for those trying to reach Reno-Tahoe International Airport.

Farther south and east, Arizona is dealing with its own version of the storm. In and around Flagstaff, which sits at about 7,000 feet, showers in the forecast for town correspond to snow over neighboring peaks and routes that climb even higher.

Roads such as Interstate 17 between Phoenix and Flagstaff and Interstate 40 from Flagstaff toward New Mexico often see sharp weather gradients, with drivers moving from dry desert freeways into rain, then sleet and snow within a few hours of driving.

The elevated sections of these interstates can accumulate snow and turn icy, especially after dark when temperatures dip below freezing. Local officials often respond with speed restrictions and, in some cases, short-term closures to allow plows and sanders to work. Travelers are urged to ensure that their vehicles are winter-ready before leaving milder metro areas like Phoenix and Las Vegas for holiday trips into the mountains.

Airports Braced for Delays as Storm Affects Western Hubs

The weather impacts are not confined to the highways. Major West Coast and interior western airports are bracing for weather-related delays as rain bands and mountain snow affect both arrivals and departures.

In Northern California, Sacramento International and Bay Area airports face bouts of moderate to heavy rain and gusty winds that can slow operations, especially when coupled with low clouds that force aircraft to rely on instrument-based landings.

Farther north, airports like Portland see a similar pattern of showers and low ceilings, conditions that typically reduce capacity and can trigger minor backups that grow longer during peak holiday periods.

Some flights may use longer routing to avoid the bumpiest air, and air traffic controllers often must space aircraft farther apart when visibility is reduced, cutting down on the number of arrivals and departures per hour.

In the mountains, snow affects aviation in a different way. For airports at higher elevations, such as Reno and Flagstaff, active snow showers can require frequent deicing of aircraft and plowing of runways and taxiways.

These operations take time, and even when they are standard procedure in winter, they can still cascade into delays when planes depart their gates behind schedule. Passengers transiting through major hubs in the West today are advised to monitor their airline apps and be prepared for longer lines at check-in and security.

Holiday Travelers Urged to Prepare for Slower Conditions

As holiday travel remains near its peak, state transportation agencies and weather services across the region are emphasizing preparation and patience. Motorists are being reminded to allow more time than usual, to slow down in heavy rain and on snowy roads, and to avoid sudden maneuvers that can lead to skids.

Carrying basic winter gear, including blankets, extra food and water, flashlights and phone chargers, is also recommended for those heading into higher terrain where closures and spinouts can trap vehicles behind blockages for extended periods.

Officials are also highlighting the importance of checking multiple information sources before setting out. State-run travel sites and 511 phone systems provide updates on chain requirements, lane closures and accident scenes, while local media outlets and social channels from highway patrol agencies offer on-the-ground perspectives.

For flyers, most airlines are encouraging passengers to confirm flight status before going to the airport and to sign up for text or app notifications in case of schedule changes.

With the atmospheric river pattern projected to linger into the weekend in parts of California and the interior West, today’s impacts are not expected to vanish abruptly at midnight.

Instead, travelers may face a rolling series of delays, improving in some areas as the storm shifts east while new trouble spots emerge where rain bands and snow squalls redevelop. Those with flexible schedules may find it wise to consider earlier or later departure windows to avoid the heaviest bands of precipitation.

What to Watch on Key Western Interstates and Passes

Several interstate corridors are under particular scrutiny today as the storm’s moisture and wind interact with mountainous terrain. Interstate 5, running from Southern California through the Central Valley and north into Oregon, remains a central route for both passenger vehicles and freight.

Heavy rain and isolated flooding concerns are most pronounced in portions of California, while farther north, frequent showers and standing water can make conditions challenging around metropolitan Portland and through the southern Oregon Cascades.

Interstate 80 over the Sierra Nevada stands out as one of the most weather-sensitive routes, with chain controls already in place on some segments and the potential for additional restrictions as new snow accumulates.

Travel between the Bay Area, Sacramento, Reno and points east can slow dramatically when a combination of snowfall, collisions and commercial vehicle spinouts forces lane closures at higher elevations.

Motorists are urged to consider alternative timing or lower-elevation routes when possible, and to avoid driving unprepared vehicles into chain control areas.

In Arizona, Interstate 17 and Interstate 40 are the main corridors at risk, as they climb from low desert basins to higher plateaus. Short stretches near Flagstaff can see winter weather that contrasts sharply with conditions a few hours to the south near Phoenix.

Road cameras and traveler information systems often illustrate this gradient in real time, and agencies encourage drivers to consult these resources before committing to mountain crossings during the heaviest precipitation.

FAQ

Q1: Which Western states are seeing the most significant travel impacts today?
California, Oregon, Nevada and Arizona are among the most affected, with California’s Central Valley and Sierra Nevada, Oregon’s Cascades, Nevada’s Sierra-adjacent corridors and northern Arizona’s high country all experiencing a mix of heavy rain, mountain snow and gusty winds that slow travel.

Q2: What are the biggest risks for drivers in the affected areas?
The main risks include slick and flooded roads from heavy rain, reduced visibility in downpours or blowing snow, icy conditions on higher passes, and sudden slowdowns caused by spinouts, collisions or debris on the road. In some mountain areas, rockslides and mudflows are an additional concern.

Q3: How are mountain passes like those in the Sierra Nevada being affected?
Mountain passes in the Sierra Nevada are seeing accumulating snow, especially above pass level, which has led to chain controls and slower speeds. Periods of heavier snowfall and strong winds can temporarily reduce visibility to near whiteout conditions, prompting short-term closures while crews clear the roadway.

Q4: Are major airports in the region experiencing delays?
Several major airports in the West are seeing weather-related disruptions, including those serving Northern California, the Pacific Northwest and some interior cities such as Reno and Flagstaff. Rain, low clouds and gusty winds reduce arrival and departure rates, while snow at higher elevations increases the need for deicing and runway clearing.

Q5: How might this storm affect connecting flights across the country?
Delays at Western hubs can ripple through the broader air travel network, especially during a busy holiday period. Aircraft and crews delayed by weather in the West may arrive late to their next assignments, which can cause downstream schedule adjustments and additional delays for flights in other regions.

Q6: What should drivers do before traveling through high-elevation areas today?
Drivers should check the latest road conditions and chain requirements, ensure their vehicles are equipped with appropriate tires or traction devices, top off fuel, and pack winter supplies such as warm clothing, blankets, food, water and phone chargers. Leaving extra time and informing someone of the planned route are also recommended.

Q7: Are there specific interstates that travelers should monitor closely?
Interstates 5 and 80 in California and Oregon, along with Interstates 17 and 40 in Arizona, are particularly important to watch. These routes cross regions where the transition from rain to snow occurs and where steep grades and tight curves can amplify the impact of adverse weather on traffic flow.

Q8: How long are these conditions expected to last?
Forecasts indicate that the storm pattern affecting the West will persist through at least December 25, with lingering showers, mountain snow and gusty winds in some areas into the following days. Conditions may improve in certain corridors as the storm shifts, but secondary disturbances can keep travel slower than normal through the holiday weekend.

Q9: Can travelers rely on typical navigation apps for real-time safety information?
Navigation apps can help reroute around congestion and show estimated travel times, but they may not always reflect chain controls, closures due to snow or debris, or rapidly changing mountain conditions. Officials recommend supplementing these tools with state transportation websites, 511 systems and local traffic and weather reports.

Q10: What are airlines advising passengers to do in light of the storm?
Airlines are encouraging passengers to confirm flight status before heading to the airport, arrive earlier than usual to allow for longer check-in and security lines, and use mobile apps or text alerts for real-time updates. Travelers with flexible plans may be offered the option to change flights without additional fees during officially declared weather waivers.