By the time the Northwest’s rainy season arrives in earnest this fall, National Weather Service forecasters will have a better view than ever.
Crews this week began installing “dual polarization” technology at the Scappoose, Ore., radar tower used by the weather service’s Portland forecasting station, a change that will give forecasters a more accurate look inside storm systems as they move across the region. A new radar just built on the southern Washington coast, set to come online for the first time this month, is receiving the same treatment.
The only downside? Construction work means forecasters at the Portland station are working without the benefit of radar for the next two weeks. The shutdown comes during what’s typically a quiet end-of-summer weather pattern — and that’s by design, said warning coordination meteorologist Tyree Wilde.
“We certainly couldn’t do it in November/December,” Wilde said. “Our weather is way too active.”
Meteorologists will still use satellite imagery, ground measurements and other tools to forecast the weather in the meantime. But Wilde acknowledged it’s a bit of a gamble to work without a key technology, even for only a couple of weeks. He and other forecasters hope the arrival of “dual-pol” is worth the wait.
Here’s how it works: Most radars use only horizontal radio wave pulses, which send back a horizontal cross section of precipitation activity over a certain range. Dual polarization adds another dimension — once finished, the revamped system will send and receive both horizontal and vertical pulses that capture a more complete picture.
The change will give forecasters a better estimate of total precipitation, and a better tool to spot areas of heavy rainfall that can produce flash flooding. Perhaps most notably, dual polarization allows meteorologists to distinguish different types of precipitation at different altitudes within the same storm as it’s happening. That should help short-term predictions for hail and low-elevation snow, notoriously tough to pin down.
“This is when the radar can go in and basically dissect the storm,” Wilde said.
Don’t expect a flawless five-day forecasts just yet. Predictions will still swing-and-miss once in a while, said Bill Schneider, science and operations officer with the weather service.
“It’s not the end-all of weather forecasting,” Schneider said. “It’s another tool.”
The new technology could also help track extreme weather conditions. In the event of a tornado, for example — remember, Aumsville, Ore., saw one just last year, and a twister touched down in Clark County in 2008 — dual-pol radar will pick up flying debris that the old system wouldn’t have seen.
When the upgrade is finished next week, Portland will be among the first forecasting stations in the nation using dual polarization technology. The new Washington coast radar, located in Grays Harbor County, will cover an area previously blocked by topographical limitations.
“This produces a good look at storms coming in off the Pacific,” Schneider said.
The Portland station’s two radar towers should be producing new data by the end of this month. The National Weather Service hopes to have dual polarization technology installed in all of its 122 radar stations in 2013, at a cost of about $225,000 each. Thirty-eight other radar stations owned by the U.S. Air Force and the Federal Aviation Administration will also be upgraded.
Meteorologists in the Portland station have spent recent weeks in training to digest new data they haven’t seen before, Schneider said. That makes dual polarization radar a research tool as much as a forecasting tool, he said.
Forecasters in Portland will likely have some time to get used to the new system before it sees a lot of action. On Monday, when construction of the new system started, crews worked under clear, sunny skies.
“On a day like today,” Schneider said, “we’re not using the radar anyway.”