Scientists can predict storms such as the one that struck the Bay Area on Sunday with some clarity when the systems are over the ocean. But once they make landfall, what happens becomes a little murkier.
The National Oceanic and Atmospheric Administration announced Monday in San Francisco that it has formed a sensor network statewide that will help track storms and better predict floods.
Hundreds of monitoring stations are being installed to form the $11 million system, according to Marty Ralph, a NOAA research meteorologist. There are four types of sensors that will, in real time, measure the wind, moisture in the air and soil saturation, and whether precipitation falling at higher elevations is rain or snow.
Michael Dettinger, a research hydrologist for the U.S. Geological Survey, said that when a heavy storm drops rain across a large flood plain that has already been saturated, the risk for flooding increases.
The new tools are intended to track storms over land, especially for atmospheric river systems such as the three that have hit the region since Nov. 28 and the one forecast to drop more rain on the region today and Wednesday.
Atmospheric rivers, which transport water vapor in the atmosphere, are important for the West Coast since just a few of the storms account for nearly half of the region’s annual rainfall, according to the NOAA. Most storms here are weak, but others, like the one Sunday, can bring strong winds and heavy rainfall, said Kevin Baker, a Bay Area forecaster for the National Weather Service.
“When you forecast, there are at least two aspects that are important to us. One is getting the weather right,” Dettinger said. “But the other aspect of the forecast is how much flooding is going to result from it.”
The flood predictions are important in helping to manage water reservoirs, releasing water from dams and warning people about flooding. Slight changes in a storm, such as when snow turns to rain at high elevations, can change flood predictions, Dettinger said.
The sensors will offer key information for decision-making, Ralph said.
The system — paid for through a state bond passed to improve water infrastructure — could be more important as global warming increases the chances that more powerful storms will hit the West Coast, Dettinger said. Several models show that large atmospheric river systems at the end of the century could carry up to double the moisture, he said.
“Global warming,” he said, noting that studies are still under way, “is likely to add in a few megastorms, if you will, of a scale that we may not have encountered historically.”