Tuesday, December 11, 2012
The heavy rainstorm that pounded northern California with up to 15 inches of rain last week was caused by what’s called an Atmospheric River. It’s like a conveyor belt of rainstorms that stream in from the Pacific Ocean.
A new, advanced weather system will warn people of powerful winter storms and help mitigate the risk of flooding.
An atmospheric river doused San Diego in December of 2010 with a full week of heavy downpours and destructive flooding.
The four coastal observatories will include:
· A Doppler wind profiling radar, which reveals the speed and direction of winds at several altitudes aloft;
· A technique for extracting critical information from wind profiler data-the level in the atmosphere where falling snow turns to rain;
· Global positioning system (GPS) water vapor instruments, which measure the total amount of water vapor above the site; and
· Standard meteorological instruments (relative humidity, temperature, pressure, rain gauge).
Source: Scripps Institution of Oceanography
Atmospheric rivers hit the state an average of 12 days per year, according to Mike Dettinger, a hydrologist with U.S. Geological Survey and a researcher with Scripps Institution of Oceanography.
Dettinger helped design new weather monitors that are being installed along the California coast that can provide specific information about the storms several days in advance. He said the information will help officials accurately predict flooding.
"So we can better understand where most of the precipitation is going to fall, where it’s falling as rain rather than snow, and we also need to know better where the soils that are being rained on are very wet versus ones that are dry enough to sort of soak up most of the rain," said Dettinger.
Dettinger said the storms will increase in frequency and intensity if the climate continues to warm.
"Climate change may well bring us a new class of these storms that would be bigger than anything we've seen in the historical record by a considerable amount," Dettinger said.
An atmospheric river is more than twice the size of an average Pacific storm, said Dettinger. "If you sort of throw all the other storms together and figure out what the average amount of water that comes out of them is, the atmospheric river on average is about 85 percent larger."