Dangers to life, property remain high in California as storm onslaught continues

California has faced a frenzy of storms that have unleashed deadly impacts since the end of 2022, and AccuWeather meteorologists say the onslaught is far from over. One storm in the bunch was already aiming a firehose of moisture at the Golden State at the start of the week and will continue through Tuesday. The rainfall could potentially lead to localized "catastrophic" flooding, in addition to widespread mudslides and road closures, forecasters say.

As a standalone storm, the amount of rain and snow expected would be enough to raise flooding concerns and snarl travel in the mountains. AccuWeather experts say what sets this storm apart and could catapult it to extreme and historic levels is the preceding conditions.

This storm was tapping into a substantial atmospheric river, and arrived just days after previous storms brought heavy rainfall and created significant flooding, increasing the impacts and risks that can occur given the already saturated ground, according to AccuWeather Chief Meteorologist Jon Porter.

California officials asked President Joe Biden to declare an emergency due to the winter storms that already impacted the state, according to ABC 10. On Monday, Biden approved their request.

In the wake of a separate storm system that brought rain and mountain snow to Northern and Central California into Sunday, the main push of moisture associated with the latest Pacific storm arrived Sunday night. Waves of moisture will continue to push onshore through the first half of the week, forecasters say.

"Flooding from Northern to Central California is expected to be widespread, even catastrophic in some locations around the coastal mountains and the northern and central Sierra. Given saturated ground, much of this water to runoff into rivers where more than a dozen monitored river locations are forecast to be above flood stage, even in the Central Valley," AccuWeather Meteorologist Joe Bauer said.

The brunt of the storm on Monday was focused on an area just south of San Francisco to the north of Los Angeles.

The Alameda Creek near Sunol, California, had surged to record high levels on Monday morning. The stream reached a height of 9.36 feet at 11 a.m. local time, which was 3.36 feet above flood stage and more than a foot above the record of 8 feet. The San Lorenzo River at Big Trees, California, had surged to major flood stage for a time on Monday and had crested at 24.54 feet, which was a few feet below the record of 28.9 feet.

The most extreme flooding occurred along the Ventura River, where the severity of the floods set an all-time record. the river reached a height of 25.42 feet at 8 p.m. local time on Monday. This is higher than 24.3 feet, which was the previous record set in 1969.

In total up to a foot of rain is expected in some portions of Southern California to the west of Los Angeles, including many of the coastal mountain ranges. In this region, an AccuWeather Local StormMax™ of 24 inches cannot be ruled out.

Since Dec. 26, 2022, the downtown area had picked up more than 11 inches of rainfall prior to his storm -- a staggering 628% higher than the normal precipitation for that time frame of 1.76 inches. During that stretch, the city recorded its wettest 10-day period since the Civil War era.

The heaviest rain will overspread much of Southern California on Monday night and will continue into Tuesday, with 1-2 inches of rain expected in the Los Angeles area. However, more than double that amount can occur in localized areas, such as on the southern- and western-facing mountainsides.

GET THE FREE ACCUWEATHER APP

Have the app? Unlock AccuWeather Alerts™ with Premium+

Motorists are strongly urged not to drive through flooded roads as the water may be deeper than it appears, and in some cases, the road surface may have been completely washed away beneath floodwaters, AccuWeather forecasters say. Traveling along winding, secondary roads in hilly areas will likely be hazardous due to flash flooding and debris flows.

As if the likelihood of heavy rain and major flooding was not enough, locally severe thunderstorms will be a threat as well. The storms can produce powerful wind gusts and hail in some cases. In a few rare cases, a tornado or waterspout can spin up as well.

As the ground remains saturated and gusty winds accompany the storm, power outages and fallen trees may be more widespread compared to recent events.

Airline travelers are likely to face another round of delays and possible cancellations at the major hubs of San Francisco and Los Angeles. Even airports that are not directly impacted by this storm can face a backlog of flights as crews and aircraft are displaced.

Surging water levels on area streams and rivers are likely to lead to flooding in unprotected areas. Rising waters will test levee systems and dam spillway capabilities. Residents throughout the region are urged to have an emergency kit ready and know more than one way out of their community in the event of an evacuation.

In addition to the life-threatening rain impacts, the storm will unleash another round of heavy snow that will be measured with yardsticks and lead to snarled travel.

Initially, snow levels in the Sierra were above 7,000 feet. However, as colder air works its way across the state, snow levels were forecast to dip Monday night and could fall to 5,000 feet on Tuesday, AccuWeather Senior Meteorologist Dan Pydynowski said, adding that snow could work its way southward into some of the Southern California mountains as well.

"The snow, while making travel very difficult, will be beneficial for ski resorts and building the snowpack in the mountains, which will lead to increased water supplies later this year," Pydynowski stated.

AccuWeather's long-range experts say the pattern of prolific storms slamming the West Coast, which has already placed a significant dent in the drought, is likely to remain in place through the middle of January.

Around that time frame, the storms will tend to swing to the north and farther inland. When that happens, precipitation amounts will tend to dwindle in California but can ramp up more so over the interior West, and that could impact the Colorado River basin with more significant precipitation events.

"Storms are likely to resume during February and March, just probably not to the magnitude as is occurring now and what is likely to continue through mid-January," AccuWeather Lead Long-Range Meteorologist Paul Pastelok said, adding that Northern and Central California would be out of the drought situation by the summer months.

Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.