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Storms associated with atmospheric rivers have dumped record amounts of rain and snow in California this winter, resulting in flooding and other hazards.

The big picture: Atmospheric rivers direct tropical moisture, often from more than 1,500 miles away, toward the Golden State, where it is wrung out in the form of heavy precipitation. 

Atmospheric rivers are long, narrow highways of moisture, typically located at about 10,000 to 15,000 feet above the surface. They can travel thousands of miles and are responsible for 30-50% of the wet season precipitation along the West Coast of the U.S., according to NOAA. 

A strong atmospheric river can transport an amount of water vapor that is “roughly equivalent to 7.5–15 times the average flow of liquid water at the mouth of the Mississippi River,” NOAA has found.

Scientists have only recently gained a greater understanding of the role that atmospheric rivers play in West Coast storm events, and observed them affecting other regions of the world as well. 

Diagram of an atmospheric river hitting California.

Diagram of an atmospheric river hitting the West Coast. Image: Sarah Grillo/Axios

During the past few months, hurricane hunters operated by the Air Force and NOAA have been investigating atmospheric rivers over the Pacific Ocean and providing added data for computer models to refine their projections. 

'Threat level: This winter, California has been hit by more than a dozen atmospheric river events, many of them strong ones that have dumped upwards of 100 inches of snow at a time in the Sierra Nevada mountains, and about a foot of rain at lower elevations. 

While all this precipitation has helped ease, though not eliminate, the record drought affecting the state, there can be too much of a good thing. 

With an epic snowpack 200 inches deep in some places, reservoirs that are rising toward full levels and rivers running high, any additional atmospheric river events could cause serious flooding. 

This is particularly the case for warm atmospheric rivers, which can raise snow levels and cause rain to fall on top of the existing snow, releasing some of its water content.

Damaging flooding has already occurred in Central and Northern California during mid-March from atmospheric river events, and more may be on the way. 

Between the lines: Climate change is adding even more moisture to atmospheric rivers, enabling them to dump higher rain and snow totals. 

This is occurring because ocean temperatures are increasing, causing more heat and moisture to be transferred into the atmosphere and made available to storm systems. 

In addition, with each 1°C (1.8°F) increase in air temperatures, a particular air mass can hold at least 7% more moisture. 

Individual storms associated with atmospheric rivers can pull in even more water vapor than this, making damaging rain and snowfall more likely. 

California is still in a long-term severe drought, particularly given its depleted groundwater supplies. 

The bottom line: Studies also show that climate change raises the odds of weather whiplash events from drought to flooding and back again. 

This is noteworthy since California was already known for its feast or famine precipitation regime. 

Go deeper: Next in parade of atmospheric rivers set to slam storm-hit California

In photos: Atmospheric river floods a storm-ravaged California

Atmospheric rivers force California to manage floods during drought

Next atmospheric river brings "high risk" of flooding to soaked California

epic snowpack 200 inches deep in some places

Next in parade of atmospheric rivers set to slam storm-hit California

What is an atmospheric river? Weather event behind California floods, record snow

These weather systems can transport tropical moisture thousands of miles.

Flooding taking place in Central California from atmospheric river storms in March 2023.

Flood waters of Deer Creek spread near Porterville, Calif. on March 10. Photo: David McNew/Getty Images. 

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At least two storm-related deaths were confirmed by state officials Friday as a powerful atmospheric river storm brought heavy rain and thunderstorms, and left thousands across Northern and Central California without power.

The big picture: The National Weather Service has warned of "copious amounts of heavy snow" in the mountains and potential flooding from a "high risk" of excessive rainfall. It's also increasingly likely that another significant atmospheric river event hitting central and northern California beginning on Monday.

Dangerous conditions continue this weekend, with rain and melting snow causing "widespread considerable flooding impacts" in some regions, per NWS. 

The current system is the latest in a series of storms that have battered the Golden State this year, delivering damaging blizzards and downpours. 

The latest: More than 22,800 people remain without power in California at 9 a.m. ET on Sunday, according to PowerOutage.us.

A flood warning remains in place through Sunday night for the Salinas river, affecting Monterey county, NWS said Saturday night. Evacuation orders were issued to some areas around the river.

In Monterey County, a breach in a river embankment led to massive flooding overnight, officials said Saturday.

First responders conducted at least 56 rescues in the area overnight, the California National Guard reported Saturday afternoon. The entire town of Pajaro is now under some level of water, the Los Angeles Times notes.

Monterey County also advised Pajaro residents not to drink their tap water after potentially contaminated flood water may have gotten into the water district's wells.

Rainfall totals showed the damage from Friday. Rocky Butte in San Luis Obispo County saw 11.58 inches, per the National Weather Service. Light rain was expected to continue overnight.

The storms flooded rural communities, small highways, creeks and rivers, AP reports.

Much of California is still under some type of flood warning, watch or advisory, per the NWS. 

Flood advisories in Santa Barbara, Ventura, and Los Angeles counties expired overnight, according to the NWS. The flash flood warnings for San Luis Obispo County were also canceled, but the county still has some evacuation orders and warnings listed for the area.

Kings Canyon and Sequoia National Parks remained closed Saturday.

President Biden on Friday also approved an emergency declaration for California, authorizing FEMA to "identify, mobilize, and provide at its discretion, equipment and resources necessary to alleviate the impacts of the emergency."

Later Friday, California Gov. Gavin Newsom (D) signed an executive order to suspend regulations on permitting so that water from the storm can be captured and used to recharge state groundwater supplies.

Details: The latest barrage hit the Sierra Nevadas' Kern River Valley especially hard on Friday, with officials ordering evacuations for multiple areas in the county. The water flow was "a threat to life and/or property," the Kern County Sheriff's office tweeted.

Footage shared online showed a robust rise in a river in Kernville amid the NWS' predictions of "extreme" flash flooding — the highest threat level NWS officials can issue.

Rising rivers also forced evacuations in the coastal Santa Cruz County as mudslides and heavy rains created hazards on the road. 

Soldiers with the state's National Guard were deployed to the region Friday afternoon to support state and local first responders.

Context: Atmospheric rivers are potent because narrow currents in the air can carry vast amounts of water vapor thousands of miles — and they have hammered California so far this year.

Climate change is adding even more moisture to atmospheric rivers, enabling them to dump higher rain and snow totals, Axios' Andrew Freedman notes.

Threat level: "A dangerous excessive rainfall event is underway across much of Central California," the NWS said early Friday, adding that up to nine inches of rain could fall on snowpack and already saturated soil, causing "widespread and severe flooding impacts."

The latest storm arrived as communities in the San Bernardino Mountains were still reeling from earlier snowstorms that have killed at least 12 people since Feb. 23, per the Los Angeles Times.

Between the lines: High-risk outlooks are rare — once a decade or more for some locations — and show that the NWS is worried about dangerous weather.

A screenshot of a Yosemite National Park tweet saying it'll stay shut until at least March 16 due to the storms.

What to watch: A new major storm system arrives early next week, "delivering another round of excessive rainfall & heavy mountain snow to the West Coast," the NWS said.

Then, come midweek, more heavy rain and snowmelt could lead to fresh flooding, "particularly in low elevations and areas with shallow snowpack," per NWS.

Editor's note: This article has been updated with new details throughout.

storms that have battered the Golden State this year,

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Thousands without power as strong atmospheric river floods California

President Biden on Friday ordered Federal assistance to supplement local response efforts due to the emergency conditions.

 woman braves the flooded streets alongside splashing trucks as an atmospheric river storm slams California in Salinas, California 

A woman braves the flooded streets as an atmospheric river storm slams California. Photo: Melina Mara/The Washington Post via Getty Images

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The deadly Tropical Cyclone Freddy is threatening to make landfall in Mozambique again after lashing Madagascar for a second time as it continued its historic run Monday.

The big picture: Thursday marks 34 days since Freddy formed. It "does appear to be a new record holder for 'longest-lasting' recorded tropical cyclone," per a statement Monday from Randall Cerveny, the World Meteorological Organization's rapporteur for weather and climate extremes.

The WMO will open an investigation to confirm that record once the storm has dissipated.

Freddy has already set the Southern Hemisphere record for the highest accumulated cyclone energy (ACE), an index measuring wind energy associated with a tropical cyclone over its lifetime, per NASA.

State of play: Freddy became a named storm off the Australia's northern coast on Feb. 6.

It "crossed the entire South Indian Ocean" and made landfall in Madagascar on Feb. 21 before striking Mozambique three days later, per the WMO.

"The storm spent several days tracking over Mozambique and Zimbabwe, bringing  heavy rains and flooding," the UN weather agency said.

"It then looped back towards the Mozambique Channel and picked up energy from the warm waters and moved towards the south-western coast of Madagascar."

The impact: The cyclone killed at least 21 people during its initial destructive path across southeastern Africa and a further eight people were confirmed dead as it lashed Madagascar again on Monday, the BBC reports. 

UNICEF expressed concern Monday that heavy rainfall from the storm that's forecast to hit Malawi could worsen what's already the country's "deadliest cholera outbreak in its recorded history."

What we're watching: Mozambique’s National Institute of Meteorology expects Freddy to make landfall as a Category 3 cyclone on Friday night, with winds of about 99 mph and gusts of up to 118 mph.

For the record: The current recognized record holder is Hurricane/Typhoon John in the Central Pacific, lasted 31 days in 1994.

A screenshot of a WMO tweet saying, "Tropical cyclone #Freddy threatens Madagascar and Mozambique for a SECOND time with rain, floods. #Freddy became named storm near Australia on 6 Feb. WMO is monitoring whether it will become the longest lasting cyclone on record."

Photo: World Meteorological Organization/Twitter

Editor's note: This article has been updated with the forecast from Mozambique’s National Institute of Meteorology.

Freddy, "longest-lasting" tropical cyclone, to hit Mozambique for 2nd time

The deadly storm has killed more than 20 people and displaced thousands of others during its record run.

A screenshot of Cyclone Freddy lashing Mozambique on March 7.

Tropical Cyclone Freddy turns back to Mozambique on Wednesday. Photo: NASA MODIS

Tropical storm

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An atmospheric river event is making its way toward Northern and Central California and is expected to arrive Thursday and last through Friday.

Why it matters: This will be a milder storm than the series of blizzards that have hit the Golden State in recent weeks, delivering rain on top of snow even at mid-to-high elevations. With a near-record snowpack, that presents flood risks.

Threat level: Central coastal California and the central interior valleys could see several inches of heavy rain and a continued threat of flooding through much of next week, NOAA’s Weather Prediction Center said in an online forecast discussion.

The rain on top of snow through about 6,000 feet is likely to cause flooding, including of streams and rivers, and water loading of homes and businesses could lead to structural damage.

Over a foot of snow will be possible for parts of the Cascades and Sierras.

State of play: The "Pineapple Express" storm is drawing moist air from the subtopics near Hawaii.

It has a trajectory of moving a lot of water vapor overhead, meteorologist Daniel Swain explained Wednesday.

Atmospheric rivers are long, narrow highways of moisture that can travel thousands of miles and are responsible for 30-50% of the wet season precipitation along the West Coast of the U.S., according to NOAA. 

They have been unusually persistent and powerful so far this winter, with no signs of an impending weather pattern shift to drier conditions.

What we're watching: Computer modeling from the Center for Western Weather and Water Extremes is projecting that an AR3, or "moderate," atmospheric river event will occur.

By the numbers: The UC Berkeley Central Sierra Snow Laboratory has recorded 603 inches of snowfall since Oct. 1 as of Wednesday, qualifying as its fifth-snowiest year on record. 

Of note: The astonishingly thick snowpack in California for this time of the year has raised hopes of more abundant water supplies and a less active early fire season across the state.

But so much snow sitting at lower elevations in particular is also a concern this week.

The dramatic swing from historically dry to very wet conditions in parts of California is consistent with what climate studies show will occur more frequently and sharply in coming decades.

Meanwhile, the San Bernardino and San Gabriel mountain ranges received enough snow to strand people indoors behind mounts of snow.

Big Bear City got more than 6.6 feet of snow in one week — that's the most snow since records have been tracked.

In nearby Lake Arrowhead, many roads were plowed for the first time in 10 days on Tuesday.

The heaviest rains from this upcoming storm are expected to fall north of these areas.

"Pineapple Express" storm to hit California

The rain on top of snow through about 6,000 feet is likely to cause flooding in parts of California.

Inmate firefighters clear snow off the roof of a restaurant in Lake Arrowhead, California, on March 7. Photo: Kyle Grillot/Bloomberg via Getty Images

The smoke released by major wildfires likely contributes to the destruction of ozone, the vital atmospheric shield that protects the planet by absorbing most of the sun's harmful ultraviolet radiation, according to a new study published in Nature on Wednesday. 

Why it matters: Wildfires are projected to become more frequent and intense over the coming decades due to global warming and land-use change.

A UN-backed panel of scientists estimated in January that the recovery of Earth's ozone layer was back on track. But increased levels of wildfire smoke in the atmosphere could delay that recovery, the researchers behind the new study found. 

Details: The researchers studied the aerosol from major fires in Australia during the austral summer of 2019–2020 to try to better understand the chemical mechanism behind wildfire smoke contributing to ozone degradation.

During that time, which was later dubbed the "black summer," several devastating fires scorched about 59 million acres, killed at least 33 people and killed, wounded or displaced millions of animals.

Blazes during that fire season also produced massive pyrocumulonimbus cloud towers that injected around 0.9 teragrams (nearly 1 trillion grams) of wildfire smoke into the lower stratosphere.

How it works: The researchers hypothesized that oxidized organics, particularly organic acids, within smoke released by wildfires increase the solubility of hydrochloric acid (HCl) in the lower stratosphere.

As HCl dissolves into smoke particles under stratospheric conditions, reactive chlorine species are activated and contribute to the destruction of ozone molecules, the researchers proposed.

Just one reactive chlorine atom in the stratosphere can destroy tens of thousands of ozone molecules before it reacts with another gas and finally stabilizes. After reacting with chlorine atoms, ozone breaks down into normal oxygen, which does not absorb harmful ultraviolet radiation from the Sun.

The researchers tested their hypothesis by comparing simulations of the proposed chemical process with atmospheric observations of the Southern Hemisphere mid-latitudes following the 2019–2020 Australian wildfires.

The simulations produced inconsistencies in the levels of chlorine species and ozone that were "in remarkable agreement" with the observations, which supported their hypothesis.

By the numbers: The researchers' model also suggested that smoke released by the Australian wildfires chemically depleted between 3% to 5% of the total ozone column in the Southern Hemisphere mid-latitudes in June and July of 2020.

The researchers noted that the change is relatively small compared to other forms of ozone loss in the mid-latitudes, but they stressed the effect could become more pronounced if wildfires become more frequent or intense in the future.

Between the lines: The researchers note the chemistry described in the study should also occur from wildfire smoke released in Northern Hemisphere, as well as from biomass burning, pollution and possibly aircraft emissions.

What they're saying: Susan Solomon, a climate scientist at MIT and the lead author of the study, told Axios she believes the ozone layer's full recovery may be a race between the decay of harmful chemicals called chlorofluorocarbons in the atmosphere and increasingly intense wildfires sending more smoke into the atmosphere. 

Solomon said previous studies have shown links between wildfire smoke and ozone decay, but the new study was the first to evaluate the dissolution of stratospheric chlorine compounds into smoke particles.

"That's exactly the same thing as what happens in polar stratospheric clouds, except that it's happening at temperatures that are much, much warmer, because the oxidized organics have such a high solubility of hydrochloric acid," she said.

Alan Robock, a climate scientist at Rutgers University who is not associated with the study, said the findings will help climatologists make more accurate predictions about how smoke in the stratosphere may affect weather and atmospheric circulation.

"We need to understand how the whole system works in order to predict what will happen and also to understand how global warming can affect climate change," Robock told Axios.

Go deeper: Study finds that critical climate thresholds may be nearer than thought

Study finds that critical climate thresholds may be nearer than thought

Study: Increased wildfire risk could delay ozone layer's recovery

Wildfires are projected to become more frequent and intense over the coming decades due to global warming and land-use change.

Firefighters watching a large bushfire burn from Bargo, Australia, in December 2019.

Firefighters watching a large bushfire burning near Bargo, Australia, in December 2019. Photo: Peter Parks/AFP via Getty Images

Wildfires

Tornadoes were reported in Texas and Louisiana as an intense line of storms slammed over Thursday night, bringing damaging winds of up to 75 mph.

The big picture: Tornado watches were issued for some 3.8 million people in Texas and across the South Thursday night, as the storm system caused widespread power outages in Texas and hundreds of flights into and out of Dallas Fort-Worth Airport were canceled. 

tornado watch has been issued for parts of Arkansas, Oklahoma and Texas

Photo: NWS Weather Prediction Center/Twitter

Threats of heavy rains, flash floods and severe thunderstorms stretched across the Southern Plains, Lower Arkansas Valley, Lower Mississippi Valley, Tennessee Valley, Ohio Valley and Southeast from late Thursday into Friday.

Zoom in: Police in Weatherford said a tornado struck the Texas city that's just east of Dallas Wednesday evening and at least one tornado was confirmed in Louisiana as tornado alerts were issued in Arkansas and Oklahoma.

Hail as large as three inches as well as an isolated embedded tornado were possible in North and Central Texas Thursday evening, the National Weather Service's Fort Worth office warned.

Residents in the Fort Worth area were told that if they get phone alerts and hear sirens, it's for wind speeds as strong as a weak tornado and they should seek shelter.

Meanwhile, in the McKinney suburb of Dallas, four tractor-trailers were overturned on a highway, police said. Minor injuries were reported.

By the numbers: More than 156,000 people were without power in Texas as of 2:30am Friday ET, per Poweroutage.us.

Zoom out: The storm line comes days after a severe storm system unleashed powerful winds and triggered tornado warnings for Texas, Kansas, Missouri and Oklahoma.

Editor's note: This is a breaking news story. Please check back for updates.

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Tornadoes reported in Texas and Louisiana as storms lash the South

At least 1 tornado was confirmed in Louisiana and hundreds of thousands of people are without power in Texas.

A satellite image of thunderstorms hitting the Southern Plains and Mississippi Valley on Thursday evening, with white dots showing lightning detected by satellite. Image: CIRA/RAMMB

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California Gov. Gavin Newsom declared a state of emergency in 13 counties late Wednesday due to this week's severe winter storms, as major snowfall forced parks in the state to close.

The big picture: While the extreme precipitation eased across the state, millions were under freeze alerts and Yosemite National Park closed indefinitely as it reported record snowfall at low elevations Wednesday. 

Meanwhile, Newsom proclaimed an emergency for the counties of Amador, Kern, Los Angeles, Madera, Mariposa, Mono, Nevada, San Bernardino, San Luis Obispo, Santa Barbara, Sierra, Sonoma and Tulare to support disaster response efforts.

Officials in those counties are working to repair highways and other infrastructure damaged in the storms, while snow has stranded people in and around Lake Arrowhead.

By the numbers: A Yosemite National Park official told the Los Angeles Times that 40 inches of snow had fallen at low elevations in the Yosemite Valley — breaking the record 36 inches set in 1969.

The Sierra Nevada was also close to seeing records tumble, as the UC Berkeley Central Sierra Snow Lab reported that it's "now at 205% of our average snowfall to-date and are at 138% of our annual peak SWE [snow-water equivalent]."

In photos: Massive snowfall across California

A person gets a high-angle view from the Walt Disney Concert Hall as it is viewed with the snow-capped San Gabriel mountains at sunset after historic rain and snow dumped on Southern California Wednesday, March 1, 2023 in Los Angeles. 

The Walt Disney Concert Hall in Los Angeles, near the snow-capped San Gabriel mountains, at sunset on March 1 after historic rain and snow dumped on Southern California. Photo: Allen J. Schaben/Los Angeles Times via Getty Images

Homes and vehicles are inundated with snow in Sugarloaf in California's San Bernardino Mountains on March 1. Photo: Brian van der Brug/Los Angeles Times via Getty Images

 A man slips while walking on an icy road as residents throughout the San Bernardino Mountains remain trapped in their homes by snow on March 1, 2023 in Running Springs, California. 

A man slips while walking on an icy road in Running Springs, California, as residents throughout the San Bernardino Mountains remain trapped in their homes by snow on March 1. Photo: David McNew/Getty Images

A Cal Trans employee turns away a driver as they attempted to gain access to Wrightwood on Highway 2 near Highway 138 Wednesday, Mar. 1,.

A Cal Trans employee turns away a driver as they attempted to gain access to Wrightwood on Highway 2 near Highway 138 on March 1. Photo: Will Lester/MediaNews Group/Inland Valley Daily Bulletin via Getty Images

The Hollywood sign stands in front of snow-covered mountains after another winter storm hit Southern California on March 01, 2023 in Los Angeles.

The Hollywood sign stands in front of snow-covered mountains  in Los Angeles on March 1. Photo: Mario Tama/Getty Images

A woman from La Puente shovels snow out of her family's rental property  in Wrightwood so they can move their vehicles on Wednesday, Mar. 1.

A woman shovels snow so her family can move their vehicles in Wrightwood, California, on March 1. Photo: Will Lester/MediaNews Group/Inland Valley Daily Bulletin via Getty Images

A pedestrian crossing the street in downtown Los Angeles is silhouetted against the snow-capped San Gabriel mountains at sunset after historic rain and snow dumped on Southern California in on Wednesday, March 1, 2023 in Los Angeles.

A pedestrian crossing the street in downtown Los Angeles is silhouetted against the snow-capped San Gabriel mountains at sunset on March 1. Photo: Allen J. Schaben Los Angeles Times via Getty Images

A bus tries to drive in the snow-slammed Yosemite National Park on Feb. 27

A bus in Yosemite National Park as highlighted in a Yosemite National Park Service online post announcing its closure on Feb. 27. Photo: Yosemite NPS/Instagram

California declares emergency in 13 counties as snow closes parks

Yosemite and other parks in the state have closed due to massive snowfall.

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