California could face a winter marked by powerful storms, flash flooding, and major disruptions to highway transportation. The National Oceanic and Atmospheric Administration (NOAA) has confirmed that El Niño continues to strengthen in the Pacific Ocean and could reach unprecedented intensity in records dating back to 1950.

According to NOAA’s Climate Prediction Center report released October 8, there is an 83% chance that El Niño will exceed the intensity of all previously recorded events during the October–December 2026 period.

The outlook also indicates that El Niño could remain strong or very strong into early 2027, coinciding with California’s rainy and snowy season.

For truck drivers and trucking companies, these conditions make highway monitoring particularly important, especially along major freight corridors connecting ports, logistics hubs, and distribution centers throughout the state.

However, one distinction is essential: the 83% figure refers to the probability of record El Niño intensity, not the likelihood of widespread flooding across California. While a stronger El Niño can influence seasonal weather patterns, it does not guarantee exceptionally heavy rainfall in every region.

Why El Niño Could Bring Heavy Rainfall

El Niño develops when surface waters in the equatorial Pacific Ocean become warmer than normal, changing atmospheric circulation patterns.

During September, NOAA measurements detected temperature anomalies exceeding 4°C (7.2°F) in parts of the eastern equatorial Pacific. Meanwhile, the Niño 3.4 index, a key indicator used to track El Niño conditions, reached +2.1°C.

These conditions can change the position and strength of the jet stream, which helps steer storm systems across the United States.

During winters associated with strong El Niño events, Southern California generally has a greater chance of receiving above-average precipitation. However, conditions can vary considerably across Northern California and the state’s mountainous regions.

Meteorologists therefore distinguish between seasonal climate outlooks and specific weather warnings. Seasonal forecasts identify broader trends over several months, while weather warnings address individual storms and their potential impacts on travel.

Flash Floods, Mudslides, and Highway Closures: The Biggest Risks

For commercial trucking, one of the most serious threats is flash flooding.

When a storm produces large amounts of rainfall in a short period, drainage systems can become overwhelmed, leaving highways underwater within minutes.

The danger is particularly significant in underpasses, low-lying areas, freeway ramps, and roads near normally dry streambeds.

Another major concern involves landslides, mudslides, and debris flows, especially in mountainous areas affected by recent wildfires.

Heavy rainfall can carry soil, rocks, vegetation, and other debris onto highways, forcing road closures until maintenance crews can clear the roadway and confirm that travel is safe.

Under these conditions, heavy-duty trucks may face additional hazards, including reduced visibility, loss of traction, standing water, and temporary traffic restrictions.

The consequences extend beyond road safety. Prolonged closures can disrupt delivery schedules, force carriers to reroute shipments, and create significant delays throughout the supply chain.

Which California Highways Could Face the Greatest Disruptions?

California has some of the nation’s busiest freight transportation corridors. Although it is too early to determine which highways could close this winter, several routes require close attention during major storms.

Interstate 5 (I-5), the state’s primary north-south transportation corridor, passes through mountainous areas and locations where heavy rain, strong winds, and snow can affect traffic. The Grapevine, between Los Angeles and the Central Valley, is particularly vulnerable to winter weather disruptions.

Interstate 80 (I-80), connecting California and Nevada through the Sierra Nevada, can also experience restrictions caused by snow, ice, and hazardous driving conditions.

In Southern California, I-10, I-15, and highways crossing desert and mountainous areas may experience localized flooding, debris accumulation, and temporary closures during intense rainfall.

Coastal highways face additional risks, as high tides and powerful waves can worsen erosion and flooding.

One example of preventive infrastructure work involves State Route 37, which connects Vallejo and Novato in the San Francisco Bay Area. Caltrans scheduled an approximately 55-hour closure beginning October 23 to reinforce a section vulnerable to erosion and flooding.

The project includes raising part of the roadway and strengthening its structure ahead of the winter storm season.

Sierra Nevada: Snow, Rain, and Potential Flooding

El Niño could also affect the Sierra Nevada, although that does not necessarily mean heavier snowfall at every elevation.

When storms bring relatively warm air into the mountains, the snow level can rise, producing rain in areas that would normally receive snow.

This can increase runoff and contribute to rising rivers and streams, particularly when rainfall combines with melting snow.

At higher elevations, those same storms may produce substantial snow accumulation, creating additional challenges for commercial vehicles traveling through mountain passes.

Caltrans warns that winter conditions may require chain controls and temporary highway closures. Commercial drivers should review truck restrictions and winter driving recommendations before traveling through these areas.

What Truck Drivers Should Do Before Hitting the Road

The National Weather Service (NWS) advises drivers never to attempt to cross flooded roads, even when the water appears shallow.

According to its Turn Around, Don’t Drown safety campaign, approximately two feet of moving water can carry away many vehicles, including some large vehicles and trucks.

Water depth, current strength, and the condition of the pavement beneath the water can be difficult or impossible to assess from inside a truck cab.

For trucking companies and independent drivers, advance planning will be especially important during periods of increased storm activity. Checking weather alerts, identifying alternate routes, and allowing additional travel time can help reduce risks.

The official Caltrans QuickMap provides information on highway closures, traffic incidents, chain controls, traffic cameras, and current road conditions.

Drivers can also check restrictions through California Highway Information or call 1-800-427-7623.

The National Weather Service issues flash flood warnings, winter storm alerts, and other weather advisories that may affect highway safety.

For motor carriers, reviewing routes before dispatching trucks, maintaining communication with drivers, and preparing for potential disruptions near distribution centers, ports, and freight terminals can help minimize operational problems.

When Will El Niño’s Impact Become Clearer?

NOAA will continue updating its forecasts over the coming weeks. The next El Niño outlook is scheduled for November 12, 2026.

In the meantime, seasonal forecasts can help identify regions with an increased likelihood of above-normal precipitation. However, they cannot predict months in advance which highways will flood or exactly when the most severe storms will occur.

This distinction matters for the trucking industry: California is not currently under a statewide flood warning for the entire winter. Instead, the state faces a climate outlook that could increase the risk of severe storms and highway disruptions.

With El Niño potentially reaching record intensity and remaining strong into early 2027, trucking companies and commercial drivers will need to closely monitor weather forecasts and highway conditions throughout the coming months.

Extreme weather makes having the right insurance coverage more important than ever. Protect your truck, your cargo, and your business by making sure your policy meets your needs. Contact our team at Saint George Insurance Brokerage for expert guidance, and review your coverage before hitting the road. Always travel insured.