Atmospheric River Threatens California With Floods

Atmospheric River Threatens California With Floods

An atmospheric river is a region in the atmosphere that transports water vapor. When it reaches land, these vapours condense into rain or snow.

Winter storms in California have the potential to devastate California's water supply. This week, storms are forecasted to bring record amounts of rain, flash flooding and mudslides to parts of the state still recovering from earlier floods.

Flood Risk

California is currently suffering from floods caused by weeks of heavy rain and snowfall. While the recent precipitation has helped alleviate drought conditions and prevent wildfires, California could soon experience another round of the same with an atmospheric river that could bring even more precipitation and snowfall.

The atmospheric river is a type of storm that brings dense, subtropical moisture from Hawaii's warm Pacific waters and will make its way towards California this week. Combining with snowfall in the mountains and some lower elevations due to earlier storms, this could create flooding conditions in low lying areas of California.

Forecasters anticipate the greatest impacts will be felt in northern and central California as well as along the coast. The National Weather Service has warned that this atmospheric river could cause widespread flooding throughout these areas.

Storms are expected to cause high winds and thunderstorms throughout the region on Thursday, strengthening as it moves inland into Friday.

Flooding risks will be greatest in areas below 5,000 feet in elevation. Rainfall combined with rapid snow melt will cause rivers and streams to overflow, potentially leading to mudslides or debris flows in some places.

According to AccuWeather Senior Meteorologist Paul Pastelok, up to two feet of rain is possible in some parts of the state. The rain will mainly fall on coastal mountains and lowlands but may mix in with some snow that has accumulated there.

By Friday, this system is expected to move inland into the Sierra Nevada mountain range. Expect heavy downpours throughout northern and central California's mountains with rainfall totals ranging from 6 to 10 inches.

The weather service has warned of widespread flash flooding in areas where rivers are already near full, such as Salinas and San Lorenzo rivers. Furthermore, flash flooding is likely to occur in some creeks and smaller streams throughout California. To prepare for this event, residents are being encouraged to stock up on supplies and deploy sandbag stations in high-risk areas.

Snowmelt

An atmospheric river set to hit California Thursday will increase the risk of flooding in a state still recovering from earlier storms. The flooding potential comes from rain falling on top of snowpack built up in California's mountains due to nine atmospheric rivers early this winter and later storms caused by an arctic air burst.

Forecasters predict heavy rain throughout the state, increasing the likelihood of flash flooding and mudslides in mountain canyons where creeks could overflow. Furthermore, National Weather Service meteorologist John Reppert believes warmer temperatures could also accelerate snowmelt at higher elevations.

Reppert noted that residents in the Sierra Nevada foothills are particularly vulnerable to flooding, but this threat also extends to coastal ranges and inland mountains. The forecast calls for 1.5-3 inches of rain in urban areas and 3-6 inches along coastal mountains and hillsides.

Thursday afternoon, a storm will make its way into the state, peaking overnight and early Friday. However, its effects will last into the weekend. According to the National Weather Service (NWS), coastal areas and lower mountain passes could see up to 3 inches of rain; high-elevation passes may see up to a foot of snowfall.

Furthermore, warmer temperatures could accelerate snowmelt in mountain passes where temperatures have been rising, potentially leading to flooding of nearby streams and reservoirs due to an influx of water. According to the weather service,

Reservoir managers have already begun releasing water in anticipation of heavy inflows through the weekend, similar to several atmospheric rivers that hit California during January and February. While this flooding has improved drought conditions, it also caused significant damage to properties and roadways.

In addition to flooding, this storm poses the potential risk of mudslides and power outages in many areas. The National Weather Service has issued various flood alerts, while state agencies are working hard to alert those living in high-elevation areas about potential flooding and road closures as this storm approaches. Residents living in these high-elevation regions should consult their local authorities about potential flood risks as well as any road closures due to this storm.

Mudslides

An atmospheric river moving across the Pacific Northwest will bring rain Thursday and Friday to California, potentially resulting in flooding at lower elevations where snow has already melted, weather forecasters warn. Furthermore, this storm could trigger mudslides on already burned-over ground from recent fire seasons, according to the National Weather Service.

In January 2023, an atmospheric river passed through California and caused widespread floods and mudslides that killed 22 people. Areas affected included Southern California, Central Coast and Northern California.

Atmospheric rivers are a type of weather system that brings heavy tropical moisture and strong winds to the United States, often leading to widespread flooding and property damage. In past years, these storms have claimed at least 20 lives and caused billions of dollars worth of destruction.

However, California is bracing for another round of atmospheric river-fueled storms due to this year's wet winter, which have eased drought conditions but left millions with waterlogged ground that's susceptible to flooding and mudslides. As such, officials are warning those living in high-risk areas to make sure they have enough food and water for at least two weeks.

On Thursday morning, a storm with rain, snow and wind made its way into Northern California's interior. Forecasters anticipate it spreading inland throughout the weekend before another atmospheric river arrives next week. As it moves into Central California's foothills, up to 3 inches of rainfall could fall in some areas according to the National Weather Service.

Though this storm isn't expected to cause as much destruction as other flood-prone events, it could still trigger mudslides in areas already under snow, particularly mountainous regions. According to National Weather Service senior forecaster Bob Oravec, melting snowpacks in these places could put additional pressure on already thin patches of snowpack and increase avalanches' risk.

The storm will also bring wind, leading to power outages and damaging tree limbs. Furthermore, it could wreak havoc on roads and other infrastructure in areas still recovering from harsh winters of the past several years, according to The Los Angeles Times.

Road Closures

Atmospheric rivers, or narrow bands of moisture that can travel thousands of miles through the atmosphere, are forecast to bring widespread rain and snowfall to California this week.

Forecasters are calling for 2 to 4 inches of rain across much of California, with isolated totals of up to 8 inches possible. Swain warned that flooding risks would increase during this storm as soils throughout Northern California have already become saturated.

He warned of an increased likelihood of slope failures - such as mudslides, landslides and debris flows - which could result in flooding. Furthermore, the NWS warned of a high probability of levee breaks due to this weather system, leading to major flooding and destruction to properties and infrastructure.

Thursday and Friday, a strong atmospheric river is forecasted to move into California. Forecasters anticipate heavy rainfall throughout San Francisco Bay area as well as parts of the Central Coast. According to the National Weather Service (NWS), widespread rainfall totals between 2 to 4 inches may fall Thursday through Friday.

On Saturday morning in the Sierra Nevada mountains, a "heavy snowstorm" is forecasted with up to two feet of accumulation possible, according to the National Weather Service. They warn that driving in these conditions can be treacherous and urge people not to venture out unless absolutely necessary.

On Saturday, the city of Sacramento shut down portions of highways as officials advised drivers to use chains or four-wheel drive on their vehicles. Additionally, the storm caused many power outages - up to 153,000 homes could have been affected.

On Wednesday, Governor Gavin Newsom extended a proclamation of emergency to 21 additional counties spanning nearly the entirety of California. He acknowledged the work done by local and state agencies who have been mobilizing in preparation for snow and flood emergencies.

According to him, the state's transportation department and other agencies are gearing up for a vigorous effort to clear roadways and guarantee public safety. With an expanded proclamation, more resources will be allocated towards combatting flooding issues as well as other winter-related challenges.