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New radar dome improves weather predictions for the Pacific Northwest

New radar dome improves weather predictions for the Pacific Northwest

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Pacific Northwesterners know it's going to rain this fall and winter.

Now, with new tools in its cupboard, the National Weather Service can better forecast the intensity, location and direction of weather coming in from the west.

The weather service last week started using the new Langley Hill Doppler radar dome erected in Grays Harbor County near Copalis Beach. In addition, crews last month upgraded the Doppler radar stations at Scappoose, Ore., and Camano Island, Wash., to include "dual polarization" technology.

"It's huge," said Cliff Mass, University of Washington meteorologist and weather blogger. "Before, we were blind to the details of weather systems approaching the coast, and now we can see hundreds of miles offshore."

The previously existing radar stations — in Camano Island, Scappoose and Portland  miss a large pie-shaped region blocked by the Coast Range in Oregon and the Willipa Hills and Olympic Mountains in Washington.

The new addition covers the blind spot, plus meteorologists can monitor a band of rain coming in from 240 miles away, dissect the storm's strength and issue more specific spot forecasts.

"These upgrades give us a much better look at the precipitation type," said Tyree Wilde, a warning coordination meteorologist with the weather service in Portland. "We can see where the rain, where the snow and where ice is inside the storm. We can see where exactly the rain-snow change is occurring."

Rain intensifies as storms slap coastal foothills, blocking the clouds' eastward march. For the first time along the coast, forecasters can see exactly where those showers increase, Wilde said.

"We'll better know the strength of the storm," he said. "We can produce better flood forecasting ... and better refine our warnings."

The radar systems use the Doppler effect to measure storm velocity. Dual polarization uses both horizontal and vertical pulses to capture a more complete picture of a storm. That should help short-term predictions for hail and low-elevation snow - conditions that are notoriously tough to pin down.

"It's like being myopic, and all of a sudden you're getting your glasses; all of a sudden you can see," Mass said.

It would have been a good tool for helping warn residents before the storm that caused the Chehalis River floods of 2007, he said. It also would have helped warn residents before the 2006 Hanukkah Eve storm, which delivered a deluge of rain along with gusts of hurricane-force winds all along the coast, Mass said. Now, he said, "we'll know exactly where every low-pressure center on the coast is coming from."

The $9 million coastal radar is the first of its kind in the nation, said Dana Felton, meteorologist with the National Weather Service.

"It helps us better predict precipitation," Felton said. "The more data we get, the better. We've always been blinded."

The new coastal radar won't have much effect on longer-term forecasts, which rely on satellites, Felton added, but will improve the accuracy of shorter-term predictions.

For example, the radar might have helped last Nov. 22, he noted, when the earliest snowfall in more than a decade caused chaos across the Northwest. That incident was caused by a La Nina system, in which windier, wetter weather led to more storms than usual.

This year's chances of another La Nina are about 50-50, according to Felton.

"We're trending to a La Nina," he said, citing cooler-than-normal sea temperatures in the eastern Pacific. "That's usually the beginning," he warned.

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