Tag Archive for: Atmospheric Rivers

How Much Damage Do Atmospheric Rivers Cause

It rained in Southern California again on Wednesday.

The storm, Marty Ralph told me, was caused by an atmospheric river, a meteorological phenomenon you have been hearing more about lately as climate change drives bigger swings between tinder dry conditions and pounding rain.

And although the rain caused the usual traffic headaches and advisories against swimming at the beach, this particular atmospheric river was actually “primarily beneficial,” according to a scale that Mr. Ralph, the director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography, helped develop.

San Diego Got More Rain Than Seattle in November

Normally sunny San Diego got more rain than Seattle last month, a reverse of what residents of both West Coast cities have to come to expect.

The National Weather Service recorded just under 3 inches of rain with their monitoring station at Lindbergh Field this November, making it the wettest November on record for San Diego.

How The Atmospheric River Storm Affected Bay Area Rain Totals

Remember fire season and power outages? They seem so long ago now.

The cold storms that suddenly doused the Bay Area over the past week instantly flipped a switch from summer to winter weather conditions. But so far, they have brought radically different amounts of rain to communities across Northern California.

“We basically went from fire season to rain season in a matter of 48 hours,” said Matt Mehle, a meteorologist with the National Weather Service in Monterey. “We’re making progress, but we could still use some more rain.”

What is an Atmospheric River and Why Should Southern Californians Keep Their Umbrellas Handy?

A new storm fed by the first atmospheric river of the season is expected bring rain to Northern and Central California beginning Saturday, and cause significant travel delays and hazards for Thanksgiving travelers returning home on Sunday, the National Weather Service said.

Based on predictions of its water vapor transport capacity, this atmospheric river is classified as moderate to strong.

Can a New Approach to Managing California Reservoirs Save Water and Still Protect Against Floods?

Many of California’s watersheds are notoriously flashy – swerving from below-average flows to jarring flood conditions in quick order. The state needs all the water it can get from storms, but current flood management guidelines require reservoirs to dump water each winter to make space for flood flows that may not come. However, new tools and operating methods could lead the way to a redefined system that improves both water supply and flood protection capabilities.

Are Atmospheric Rivers the Reason for Northern California’s Extreme Weather?

It’s been a tough few years for Northern California, disaster-wise. The north state has been hammered in quick succession by catastrophic drought, intense flooding and rampaging wildfires. While it’s reassuring to know such extreme events are historically uncommon, they’re also not simply a result of bad luck.

Scientists have only recently begun to understand that they share a common natural link.

GOES satellite image of the atmospheric river phenomena from March 20, 2018.

California Funds Atmospheric Rivers Research

A better understanding and forecasting of atmospheric rivers could improve flood control and water management in California.

The 2019-20 California state budget includes $9.25 million to pay for research into how the state Department of Water Resources can more accurately track the intensity and landfall locations of atmospheric rivers. About half of the state’s annual rainfall and 90 percent of its flooding come from such events.

“Improved forecasting and monitoring of atmospheric river storms would benefit not only California, but the Southwest, in managing our water supply,” said Kelley Gage, director of water resources for the San Diego County Water Authority. “With better forecasting, water managers could also prepare and plan for flooding events caused by the atmospheric rivers.”

The science behind atmospheric rivers

The science behind atmospheric rivers. Graphic: NOAA

Rivers in the sky

Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics, according to NOAA. When the atmospheric rivers make landfall, they release the water vapor in the form or rain or snow.

“The rivers can stretch from 250 to 370 miles wide and carry a water amount more than 7 times the volume of the Mississippi River,” said Alexi Schnell, water resources specialist with the Water Authority.

The research funds were allocated to the Department of Water Resources to “improve observations, forecasts and decisions in support of atmospheric river precipitation events” as part of the DWR’s Research, Mitigation, and Climate Forecasting Program.

Atmospheric Rivers

Atmospheric Rivers in Water Year 2019. Graphic: Center for Western Weather and Water Extremes

Volatile water resources

A new study led by Scripps Institution of Oceanography at UC San Diego suggests that a new regime of wet and dry extremes is emerging in California. The study shows that the projected increase of extreme precipitation is likely to be caused by streams of moisture in the sky known as atmospheric rivers.

The study was published July 9 in the journal Nature Scientific Reports.

“California already has the most volatile water resources in the country,” according to a news release from Scripps. “Scripps scientists discovered that the state’s precipitation, as it becomes less frequent but preferentially stronger, will vacillate even more wildly between extremes of drought and flooding as a consequence of climate change.”

The federal Bureau of Reclamation, the Southwest Climate Adaptation Science Center, NOAA, the U.S. Geological Survey, and NASA funded the study, “Precipitation regime change in Western North America: The role of Atmospheric Rivers.”

California weather extremes

“As Mediterranean climate regions around the world are becoming more subtropical, the dry season is expanding. California is no exception,” said Alexander Gershunov, a climate scientist at Scripps. “What is exceptional about California is that the heavy precipitation is projected to become more extreme. We knew this from our past work. Now we have identified the mechanism responsible for this bolstering of extremes, and that gives us a more nuanced understanding of what to expect from future hydroclimate and a clearer interpretation of ongoing changes.”

 

Atmospheric Rivers helped California's snowpack in Winter 2018-19.

For the year-to-date 2019, the precipitation total was 19.05 inches, 3.74 inches above average, and the wettest such period in the 125-year record. Graphic: NOAA

Atmospheric Rivers boost snowpack

During the 2018-19 winter, atmospheric river events significantly increased snowpack in the Sierra Nevada and the Rocky Mountains. Both areas are key sources of water supply for the Southwest, including California and San Diego County.

Precipitation in the contiguous U.S. was above average from January to June 2019, according to a NOAA climate report released this week. The report said the 19.05 inches during the six-month period was 3.74 inches above average and the wettest such period in the 125-year record.

The January-to-June 2019 precipitation map showed California’s statewide precipitation was “above average” and “much above average.”