We reported on this in our 2011 special report for ARPPS members ARPPS Planning Position Paper # 4: California Dams & Auburn Dam: Policy Environment and the U.S. Geological Survey Report we quote notes:
“This document summarizes the next major public project for MHDP, a winter storm scenario called ARkStorm (for Atmospheric River 1,000). Experts have designed a large, scientifically realistic meteorological event followed by an examination of the secondary hazards (for example, landslides and flooding), physical damages to the built environment, and social and economic consequences. The hypothetical storm depicted here would strike the U.S. West Coast and be similar to the intense California winter storms of 1861 and 1862 that left the central valley of California impassible. The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years.
“Extensive flooding results. In many cases flooding overwhelms the state’s flood-protection system, which is typically designed to resist 100- to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide.”
The Sacramento Bee has run a story about NASA’s take on this a few days ago.
Scientists at NASA say they have identified a rare weather pattern that will help forecasters predict when California will experience periods of intense and potentially prolonged wet weather.
The new findings will help officials assess the possibility of floods, mudslides and levee failures, the scientists say, and will prove critical to regions where rivers are a big part of the landscape – like the Sacramento region, where the American and Sacramento rivers converge. The rivers absorb run off and melting snowpack from the Sierra Nevada, where storms typically deposit much of the state’s precipitation.
“We have found a strong connection between certain phases of two systems and the frequency of winter storms in California,” said Bin Guan, an earth sciences researcher at the University of California, Los Angeles and NASA’s Jet Propulsion Laboratory.
Guan’s study – a collaboration among scientists at UCLA and the National Oceanic and Atmospheric Administration – found a conclusive link between the alignment of two weather patterns in the Northern Hemisphere and the formation of an “atmospheric river” headed for California.
The results were gleaned in part from data provided by NASA’s 11-year-old Aqua weather satellite – one of more than 40 weather-related satellites that circle the globe.
Atmospheric rivers are narrow bands of wind, often a mile high, that can pack the punch of a hurricane. As they move over the ocean, they become laden with water vapor – and can carry with them as much water as the Mississippi River dumps into the Gulf of Mexico in an average week.
An example of the power of such an atmospheric river event was seen in 1999, when a winter storm hit California and caused 15 deaths and $570million in damage.
To arrive at his findings, Guan looked at 50 years of data, including information from the California Department of Water Resources for the winter of 2010-11, when 20 atmospheric river storms made landfall.
The two weather systems studied were the Arctic Oscillation and Pacific/North American teleconnection. These weather patterns rarely align in a certain way, but when they do the result is intense weather for California. Most troubling is that the weather events have the possibility of playing out over an extended period of time – such as the winter storms in 2010-11, said Guan.