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New weather sites will take close look at atmospheric rivers

Coastal observatories in California will measure low-level winds and moisture to generate better forecasts

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A NOAA weather graphic shows an atmospheric river streaming across the Pacific to the central California coast.

By Summit Voice

SUMMIT COUNTY — To get a better handle on the impacts of incoming “atmospheric rivers,” scientists are installing specialized new coastal observatories at Bodega Bay, Eureka, Pt. Sur and Goleta, California.

The coastal weather stations will measure low altitude winds and the amount of moisture moving ashore — key data that will help forecasters pinpoint how much precipitation is likely to fall during an atmospheric river event.

“California needs to know how and where it might rain or snow, when and where to expect flooding,” said Michael Anderson, Ph.D., state climatologist with the California Department of Water Resources. “The observatories will also help state officials and scientists monitor changes in atmospheric rivers associated with climate change.”

These powerful winter weather systems, sometimes called pineapple express storms, can be beneficial, in that they help to fill the state’s reservoirs, but they can also cause destructive floods and debris flows.

The coastal observatories, which are arrays of custom instruments, are being installed in collaboration with the California Department of Water Resources and Scripps Institution of Oceanography, University of California San Diego. The observatories will give weather forecasters, emergency managers and water resource experts detailed information about incoming storms such as winds and water content.

The move to set up the four observatories and other weather instruments throughout the state came after NOAA researchers and academic scientists spent several winters testing and selecting the most effective arrays of instruments for collecting useful information for decision makers. Installation of all four observatories is expected to be completed by early 2014.

“With satellites, we can see the tell-tale water vapor signature of an incoming atmospheric river over the ocean. However, NOAA’s offshore observing systems do not measure another key factor — strong low-altitude winds,” said Martin Ralph, Ph.D., a research meteorologist and branch chief in NOAA’s Earth System Research Laboratory in Boulder, Colo.

“With our new sensors, we’ll be able to measure those winds and more, to understand just how much moisture is moving in, which largely controls how extreme the precipitation inland will become. This information will ensure that meteorologists and emergency managers have additional information to keep the public informed about these potentially destructive storms,” Ralph said.

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).

Combined, these data allow forecasters to monitor the transport of moisture into the state, which is critical in determining precipitation amounts and locations as well as the altitudes in the mountains that will receive rain as opposed to snow.

These observatories will become part of the statewide observing network designed by NOAA scientists and colleagues to give forecasters and water managers the information they need to help to mitigate the impacts of strong atmospheric rivers, such as extreme precipitation and flooding.

For example, snow-level radars designed, built and tested by NOAA scientists, are now deployed in 10 major watersheds across the state. Also, a network of soil moisture sensors is being installed at 43 sites across the state, including several in the flood-prone Russian River watershed.

“These soil moisture sensors are key to anticipating whether an incoming storm will produce heavy runoff or if much of the rain will be absorbed in the soil,” said Michael Dettinger, a research hydrologist with the U.S. Geological Survey and a research associate with Scripps.

“This new and innovative network, transitioning research into operations, is helping California move into the future, better observing and planning for floods and water resource issues of today and tomorrow,” Anderson said.

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